Page 5.537 (9,559)
Avoiding Icing and Thunderstorms
Return to whittsflying Home Page
Forecast Ice; ...Clouds and Icing; ...Types of Icing; ...Levels of Icing; ...Icing Avoidance; ...Where's the Ice; …Ice and Performance; …Induction Ice; …Defenses Against Ice; ..Flying with Ice; ...About Ice; ...Icing Checklist; ...What's New; ...Icing Accidents; ...Birth of a Thunderstorm; ...Thunderstorm Features; ...Hail; ...Radar Classification; ...Kinds of Thunderstorms; ...Imbedded Thunderstorms; ...Squall Line; ...Tornado; ...Hurricane; ...Microburst; ...Lapse Rate; ...Convective Weather; ...Classification by Stages; ...Lightning; ...Thunderstorm Survival; ...Thunderstorm Statistics; …More on Thunderstorms; …Thunderstorm Grave Index; …Revisiting the Thunderstorm; …More on Thunderstorms and Avoidance; ...Survival; ... Flying with Thunderstorms; … Tornadoes; … Lightning; …Thunderstorm Detectors; ...Ice Ain't Nice; ...Snow Rhymes with No; ...Icing Lessons; …Climbing to Escape Ice; ...On Icing; ...Thunder Storms in Brief; ...
Here is a host of resources covering all facets of aircraft icing
The NTSB seems to think a forecast of ice provides the fact that ice exists. Contrary PRIEPS do not apply. If an icing SIGMET exists, a takeoff is considered a violation of the FARs. In the winter that is most of the time. 2/10 of weather coverage (rain or ice) means that 80% of area is rain/ice free. If there is ice in clouds, you want to stay above and out of them for as long as possible. The FAA considers "known" icing to be if "ice" appears in the forecast. It would be very difficult to fly IFR in the winter without entering an AIRMET area forecasting potential icing. The legality of filing up through an icing layer to on-top VFR is questionable.
What works to remove ice from an automobile will not work for an airplane. I once knew a pilot to use a hose. Three hours later in a heated hanger and many man-hours of drying he was able to depart. If you have ice, you can remove it in a heated hanger but the moisture should be totally removed with towels. Open the doors and get the aircraft cold before going outside. Wing surfaces above the outside temperature can cause any precipitation to melt and re-freeze on contact.
FAR 135.227 apply to air taxi and commercial operations and not to Part 91 but its advice would be well heeded. Do not depart with frost, snow, or ice on propeller, windows, engine, pitot, static, wings, or control surfaces. Internal water that may become ice and affect flight must be removed.
Pilots are required to use aircraft only in conditions for which certified. Most removal systems are specific and usually leave much ice on the aircraft. Ice adheres to the structure when the temperature is at zero degrees Celsius. If icing is encountered take action such as 180-degree turn, climb, descend or contact ATC. Altitudes 2500+ feet below the freezing level and 7500+ feet above the freezing level would under standard conditions be ice-free. Avoid visible moisture but the absence of visible moisture is not a reliable indicator of icing hazard.
Ice may not form in stratus clouds below -15 Celsius, but this is not so where there is a rapid lifting or stratocumulus behind a cold front. References are ACs 91-51, 91-13C. It should be noted that air is rising in all clouds, if clouds did not rise the moisture making the cloud would fall. In stratus clouds the air is rising less than an inch a second.
Always have a way out to where ice won't form and where any airframe ice is likely to melt. The FAA will cite you for a violation if you fly into forecast icing and have a problem. If PIREPs confirm icing, don't fly. When flying above clouds and in below freezing temperatures don't make an immediate descent into the clouds and possible moisture. Descend to the cloud level and let the aircraft warm up before getting wet. Pilots do not notice very small amounts of ice that can radically affect aircraft performance. Frost and ice so thin as to be visually undetectable can destroy the aerodynamics of airfoils.
The ability of an aircraft surface to collect ice depends on air temperature, time of exposure, curvature, the amount of water available, and the size of the droplets and the aircraft speed. Large blunt surfaces do not collect as readily as do thin sharp surfaces. The thinner tail surfaces are better collectors and show degradation effects much more readily. By the time you see ice on the wings it is too late. Laminar airfoils suffer the most from icing. Only an absolutely clean surface is safe.
The mere chance of icing is enough for the FAA and NTSB to find against a pilot who flew knowing such a chance existed. Thus, if there is visible moisture in the air, read cloud, and the temperature is below freezing, a pilot should not get into the airplane. If any ice exists in a cloud, it will be worse at the top than at the bottom. Avoid night flight if there is a chance of ice. In some areas the pilot who does not fly when there is a chance of ice, will never fly. Don't let ATC fly you into ice via a vector.
Don't fly toward icing without an escape plan. Once encountering ice get out of it immediately. You can be violated for flying into 'chance' of icing conditions.
1. Trace - noticeable; a problem in one hour
2. Light - apparent; a problem in one hour
3. Moderate - Brief exposure is a problem; divert
4. Severe - Immediate flight diversion is necessary.
Clouds and Icing
1. Kind of ice is determined by drop size
2. Amount is determined by drop distribution
3. Hazard is determined by aerodynamic effects of the aircraft
Temperature is a variable factor related to fuel, aircraft surface, and relative levels to precipitation. The most hazardous region for icing is in the mountains. Icing can occur any time of the year. As icing increases the stall speed of the aircraft increases. The approach speed of an ice up aircraft should be increased. Super-cooled clouds contain liquid very small droplets even though temperature is below freezing. (5 to 100 microns in size) Ice crystal clouds form where the moisture is frozen into in crystals.
A convective SIGMET implies severe icing. SIGMETS are issued for severe icing. AIRMETS are issued for moderate icing. Icing forecasts are now issued as AIRMETS; they cover a 6-hour period and are updated as required.
Types of Icing
Clear - hard, dense, glossy and heavy, due to slow freezing of large drops that flow and assume shape of surface. Range is +5 C to -10 C in cumulus clouds. Most likely in freezing rain since drops form continuous heavy sheet as they spread out and freeze. Changes shape of airfoil and reduces effectiveness. Thin layers difficult to see. Detectable only by touch. The worst form occurs in freezing rain. No aircraft is certified for flight into freezing rain.
Mixed - brittle and frost-like with glossy outer crust. Due to flight in mixed cloud types. Worst of both types of ice. Combination of both types since moisture is of different sized drops. Shows as hard rough accumulation. Most likely to occur in frontal zones over mountainous areas.
Rime - hard rough milky-white conglomerate due to rapid freezing of small supercooled droplets. High air content like in refrigerator. Grows on front of aircraft surfaces. Colder temperatures than clear ice below freezing in stratus or fog from -10-degrees to -20-degrees C. Forms when aircraft surface temperature is below freezing and then flies through super-cooled water droplets. Droplets freeze quickly without chance to flow. Forms on leading edges and appears rough and brittle. Similar to refrigerator ice with trapped air spaces that greatly reduce the weight.
Freezing drizzle is worse in its icing impact than is freezing rain because its droplet size causes it to impact into a coarse rough surface. Rain is a relatively low altitude occurrence that tends to run on the aircraft surface.
Ice pellets develop from falling freezing rain that fell as rain in a
warmer layer above. The liquid rain falls into colder air and becomes super
cooled. It then falls into sub-freezing air and turns into ice pellets.
--Use carburetor heat when flying in visible moisture
--Use heat when flying with reduced power
--Listen/feel uninitiated power loss or roughness---HEAT Instantly
--Freezing rain is greatest danger
--Ice changes the shape of your lifting surfaces
--It is an FAR violation to fly into forecast icing
Levels of Icing
(size/kind of aircraft a determining factor)
Trace - perceptible but not a factor in less than an hour. Rate of accumulation is slightly greater than the rate of sublimation. It is not hazardous even though deicing/anti-icing equipment is not used unless encountered for over an hour.
Light - accumulates and a hazard at one hour +. Light icing has a rate of accumulation that may create a problem if flight is over one hour. Occasional use of deicing/anti-icing equipment removes/prevents accumulation. It does not present a problem if the deicing/anti-icing equipment is used.
Moderate - Moderate icing has a rate of accumulation such that even short encounters become potentially hazardous and use of deicing/anti-icing equipment or a flight diversion becomes necessary.
Severe - Severe icing has a rate of accumulation such that deicing/anti-icing equipment fails to reduce or control the hazard. Immediate flight diversion is necessary.
Ice does not accumulate in clouds until you fly into the super-cooled droplets that exist from freezing level down to -4-degrees F. At +5-degrees F droplets freeze on the leading edges of the flying surfaces. From 28-degrees to 32-degrees the water runs back on the wings and forms clear ice. At 14-degrees to 24^ ice may freeze on the trailing edges. From the FSS you want to know where is the water and how large are the droplets. The standard briefing will always include icing information. Any forecast with 50% humidity means that there is icing up there.
A pilot should watch TV weather for several days before going on an
extended flight. Only by understanding the formation, growth, movement and
changes in the weather can the pilot learn to anticipate what is coming.
Interestingly over half of all weather related accidents show no evidence of
the pilot having either sought or received pertinent weather information. TV
weather is just the beginning. A FSS/Flight Watch specialist can pick up the
loose ends by providing currency to information that applies to a specific
route of flight.
Someone taking off with sleet falling based on the knowledge that there must be warmer temperatures aloft. Is making an assumption, although that statement may be true sometimes, it is not always the case. Taking off into sleet is quite dangerous, http://aircrafticing.grc.nasa.gov/courses.html#
Program states that a significant risk of flight in freezing rain or freezing drizzle or ice pellets is that you may run into super-cooled large droplets (SLD) at any altitude between the surface and the above-freezing layer. And that there may not necessarily be an above-freezing layer at all!
Freezing drizzle can also be formed by a process called "collision-coalescence" with NO temperature inversion (e.g. no warm level aloft). For most any aircraft, flight through SLD is a very high-risk operation!
1. Depart the area
2. Climb to above freezing temperature
3. Descend to above freezing temperatures
4. Frost should always be removed form an aircraft before flight.
5. Freezing or super-cooled rain is most hazardous of all conditions.
6. A 180 out of icing is a crap shoot.
7. Climb at reduced angle of attack to improve stall margin.
8. You can only avoid icing by avoidance of icing conditions.
Where's the Ice:
--Where's the water
--How much water
--Backflow around a low?
--Upslope lifting related to cold front?
--Get tops, bases, and temperatures.
--Relative humidity trends.
--Have TAFs been amended
--Where are the escape routes?
If encountering icing, you must get clear as soon as possible. This means climbing or descending at least 2500'. Given the choice I would recommend climbing if within aircraft capability. My reasoning for this is that if you can't climb clear at least you will have acquired some additional obstacle clearance altitude. If you can get into -20 C you are not likely to get more ice.
Ice is possible in the six to ten thousand foot level year-around when lifting occurs. Winds carry moisture so determine if you are flying the warm side or the cold side of the fronts. Amendments to forecasts mean that the forecasts were wrong in the first place. Freezing level charts are renewed every twelve hours.
Misinformation as well as misinterpretation is the major causes of icing accidents. Freezing drizzle is more dangerous than freezing rain because it leaves a rough surface.
Ice and Performance
Fuel system ice
Rime ice -2 to -10C
Clear ice -10 to +2
Worst ice at cloud tops
Loss of thrust
Higher stall speed
The specific kind of induction ice of the several available is not always determined by the kind of carburetion used by the aircraft. Impact icing that accumulates on the exterior air intakes can and will accumulate on any aircraft. Impact icing only occurs in actual IFR conditions with temperatures in the 25 F area. The first signs of impact ice appears at the edges of the windows and on the sharper protrusions of the aircraft. Freezing temperatures in the cockpit can cause the grease used to lubricate the throttle cable to congeal and make any throttle movement impossible. The pilot reaction when suspecting induction ice is to utilize alternate air. With alternate air comes a reduction in power.
A richer operating mixture comes as a result of both carburetor heat and alternate air. Leaning will improve both engine operation and increase engine heat. While Lycoming says detonation is not possible with less than 75% power with both carburetor heat and alternate air, a full power go-around presents a detonation probability. Leaning will increase engine heat and improve anti-icing capability.
Ice cannot exist unless there is water vapor present that can be frozen by cooling due to venturi effect in the carburetor or by temperature drop due to the vaporization of fuel. In either case, ice will accumulate on the interior and protrusions inside the carburetor.
The presence of ice initially causes a drop in rpm, followed by engine roughness and finally stoppage. This sequence can occur through a rage of outside temperatures from 20 F to 90 F when humidity is above 50%. My experience has been that taxiing in 50-F is a high probability zone at CCR. When outside temperature is below 14F it will be too cold to form carburetor ice UNLESS heat is applied. Don’t!
Throttle ice occurs when a prolonged descent cools the engine so that insufficient warm air is available to melt the ice. Since such icing can occur on relatively short notice, this is one reason not to make power-off landings and is one of the reasons for the FAA gave for making the change to partial-power landings as being the standard.
Get priority handling from ATC
Have an escape plan
Use carburetor heat and leave it on
Stay clear of clouds even under IFR
Check POH for minimum speed with ice
Climb immediately if you can
Control effects at altitude
Increase in approach speed
Fly down to the ground
Flying with Ice
--Avoid abrupt and steep maneuvers while carrying ice.
--Reduce the angle of attack in climbs to get out of icing.
--Do not use flaps and add speed on approach.
--Aircraft external surface temperature at or below freezing
--Ambient air temperature a degree or two above freezing
--These textbook requirements do not ALWAYS apply.
--Light aircraft should not fly in clouds and freezing temperatures.
--Plan a no-flap landing any time you have icing.
--Be aware that aircraft handling will be degraded by:
...........Loss of stability
............Reduced or loss of control
.............Possible tail stall
Rising air causes water vapor to rise and condense into water droplets. Some of these droplets may form ice crystals but others remain liquid. As cloud droplets cool to freezing and below they may fail to become ice crystals. Clouds from 0 to -10 Celsius are likely to be only super cooled droplets. The droplets do not have the required nuclei to trigger the creation of ice. Below -20 Celsius only ice crystals will exist. If these droplets become too large to be lifted they will fall as freezing rain or drizzle. A wing meeting this super cooled water will make ice on a wing surface. Icing is more likely in a cloud when the sky is clear overhead. This is because any falling ice crystals form at the expense of water droplets. The biggest cloud drops are confined to small areas or shear zones. Turbulence is a characteristic of a shear zone.
Major effects of structural icing on the aircraft itself consist of airfoil changes, weight, blocking of air intakes, loss of visibility, radio, interference, and corruption of static instrument readings.
When moisture and sub-freezing temperature are combined you have the basic ingredients for icing. The major effect of ice on an airplane is that it disrupts the smooth flow of air, increases drag and thereby the stall speed. Weight is not as critical as is the effects on airflow. For ice to accumulate the temperature has to be below freezing and the moisture visible. Icing decreases speed, lift, range, climb performance, service ceiling, visibility, radio reception, thrust, engine cooling and combustion. Icing increase gross weight, stall speed, fuel consumption, flight time and heart rate. Icing at high altitudes is not as usual as at low altitudes and when occurring is rime ice. Accumulation rate will be less.
--Have an ice escape plan.
--Preflight pitot heat.
--Know icing characteristics of flight path.
--Know where the warm air is.
--Cloud tops (ice) rises toward the low pressure center.
--Cycle boots to assure operation.
--Use shallow climb in icing conditions.
--Give PIREPs on 122.0
--Land without flaps.
--There is still a lot we do not know about aircraft icing.
1. Make a 180° turn.
2. Climb if your performance allows.
3. Use carburetor heat or alternate air.
4. Apply pitot heat
5. Defrost the windows in preference to cabin heat.
6. Apply partial flaps in the descent but not in the approach.
Metal-coated electro-thermal system imbedded in paint are in the offing. Electric eddy currents and magnetic repulsion can move ice and cause it to be shed from lifting surfaces. Another system pumps anti-freeze through small holes in the wing surfaces to prevent the formation of ice.
For the formation of ice it is required that you be in freezing temperature and visible moisture. A parked aircraft can get ice at less than freezing temperature. The worst ice occurs in freezing rain below clouds. Such icing will be quite rapid in build up. Icing disrupts lift, jams controls, chokes engines, disrupt radios, and clog inlets. It is not a safe assumption that you can tell the existence of icing conditions by visual means. The FAA finds any flight into forecast ice as 'careless operation' under FAR 91.13. FAA weather forecasts are consistently conservative because there has been no appreciable improvement in forecasting capability.
Icing as a cause of accidents seldom remains as evidence. Unless the pilot has revealed the existence of ice the investigators can only make presumptions from assumed flight conditions. About 45 General Aviation accidents due to airframe ice happen every year. PA-28s and C-182s, perhaps because of presumed performance capability, are worst offenders. In flight icing accumulation usually results in approach or touchdown accidents. Structural icing accidents are most apt to result in fatalities. While only one in six aircraft accidents result in fatalities, 56% of icing accidents result in fatalities. Almost 50% of the structural icing accidents/fatalities occurred during takeoff. A millimeter of ice on a wing will reduce lift 25%. What does this say about preflight? I once found ice on one wing and not on the other of a PA-32 during a preflight. The ice was detectable only by feel.
The rounded leading edge is one of the last places to accumulate ice although it is where pilots look first. The sharper the surface the more likely it is to get ice. This is one of the reasons tail surfaces are first to accumulate ice. The divided airflow around lifting surfaces carries most of the water droplets to freeze on the surfaces. A trace of ice on the wing implies a lot on the horizontal tail. Under-wing icing is most likely to occur during climb. The suggestion that you attempt to climb out of icing conditions may not be applicable to GA aircraft. The mention of possible icing along your flight-planned route in an Area Forecast (FA) is sufficient to make the trip 'flight into known icing'. A confirmation of ice means, 'known' icing conditions'.
Roll upset is an aerodynamic stall caused by self-deflection of ailerons that occurs in aircraft with un-powered ailerons and pneumatic deicing. Freezing super-cooled drizzle drops (SCDD) does this. The upset is triggered by some change in configuration.
Icing creates unique airfoil shapes with unique lift, drag, critical angles of attack and pitching characteristics. Once ice accumulates you become a test pilot. In icing conditions any vibration, buffet or change in handling serves as a warning that you are in serious trouble. The problem may be irreversible. It is not a good practice to fly in ice with flaps and gear extended. The accumulation of weight and drag will adversely affect performance.
Icing is not always forecast accurately since it is based on relative humidity and temperature. Anytime the OAT is at +5 C consider icing as possible. This is especially true if you are descending out of even colder air and the cold aircraft surfaces may provide a welcome home for icing. A standard lapse rate loses 2°C or 4°F for every thousand-foot increase in altitude. Knowing this basic and the airport altitude you can surmise the freezing level by subtracting 32° from the surface temperature given AWOS or ATIS, divide this difference by 4 and multiply the dividend by a thousand. This must be added to the surface altitude to find the flight altitude of freezing level.
Birth of a Thunderstorm
The warm earth begins to release heat into cooler moist air. Puffs of cumulus begin to form and rise. Two or three of the puffs merge, are warmed more and rise faster while gathering in the warm moist air from nearby. The tops of the cloud have reached colder regions of surrounding air that condenses and forms slush balls of graupel. These balls begin to fall through the cloud. The rising air from below raises the graupel hundreds of feet where it falls. This is repeated over and over as the puffy cumulus has darkened and become a cumulonimbus. The positive and negative electrical charges within the cloud have begun to separate top and bottom. The big show is yet to come.
Only 1000 of the 10,000 major thunderstorms develop tornadoes. China has a many storms but only 10 tornadoes. This is because of differences in geography and the presence or non-presence of water.
Any thunderstorm is capable of destroying an airplane. Some just do it quicker. The higher the top the greater the violence by 16,000' will be enough to do you in. The south side is worse than the north side if you for destructive violence and tornadoes.
A thundercloud can weigh 100,000 tons. (This does not include air pressure). The energy in an average thunderstorm is that of ten atomic bombs. (400 kilotons) Thunderstorms often go above cruising levels of commercial aircraft. The downburst of descending air underneath a thunderstorm have proven to be extremely dangerous to low-flying aircraft. Thunderstorm can breed tornadoes with wind speeds up to 285 mph. The vortex of a tornado may extend from the ground well into the cloud. Any flight into a thunderstorm could encounter a tornado. Never fly in the vicinity of cumulonimbus mammatus clouds. Hazardous turbulence is present in all thunderstorms. Maneuvering greatly increases the stress (G-forces) on an aircraft and should be avoided in any turbulence.
For a thunderstorm to exist you must have water vapor in huge amounts which means a very high humidity, an unstable lapse rate of over 3.5/2 degrees Fahrenheit/Celsius, and a lifting action cause by terrain or heating. When temperature increases or decreases by a 20-degree increment the relative humidity reciprocates (the opposite way) by halving or doubling. Ex: 60-degree temperatures with relative humidity of 25%. Temperature rise of 20-degrees to 80 will cause relative humidity to drop to 12 and 1/2%. Temperature drop of 20-degrees to 40 will cause relative humidity to rise to 50%.
The more lightning the more severe the storm. Thunderstorms have rounded bases with severe up and down drafts best not fought but ridden to avoid over stressing aircraft. Once caught do not turn since this also increases stress on the aircraft. Don't knowingly fly under a thunderstorm since turbulence is a given feature and is usually accompanied by a downburst or microburst of wind and water capable of increasing the aircraft gross weight beyond its climb capability.
Basic requirements are:
1. Unstable air---
2. Initial updraft---latent heat released by condensation will increase buoyancy of rising air column and create a 'burner chamber'
3. Air with high moisture content
A drop of water falling in a thundercloud is blown upward to freezing level and solidifies as ice crystals. Very often the power of the updraft is sufficient only to maintain the position of the hailstone within the cloud while the ice accumulates unlit the updraft can no longer sustain the stone and allows it to fall free of the thunderstorm. The crystals rise and accumulate more moisture and becomes a mushy lump called graupel. Graupel rises and falls again and again or may remain at one altitude, as it becomes ever larger. Some of the graupel is blown so high and freezes so hard that it is blown out of the anvil of the thunderstorm and falls as hail. From a distance falling hail is greenish in color. Flying in hail is looking at thousands of bullets coming right at you. It can strip the paint from aircraft leading edges in minutes.
Spring and summer are the main hail periods of the year since they occur during the thunderstorm season. Sleet occurs in the winter near the surface. Super cooled water drops or graupel will ice an aircraft in a very short time. Updrafts speed requires to form 1/2 hail is 22 mph. 3" hail requires 100 mph updrafts. 3/4" hail is grown in 'severe' thunderstorms.
--Extreme or severe
Damaging winds of 50+ knots, 3/4" hail, tornadoes.
--Air Mass - which develop due to surface heating. Summer afternoons are the periods of greatest activity.
--Steady State - Caused by frontal activity which can develop into squall lines and tornadoes.
Kinds of Thunderstorms
Limited state thunderstorms grow so rapidly that they self-destruct. The updraft becomes a downdraft that cools off the heat engine below and the storm dissipates. When the cloud stops raining the dissipating stage is complete. The life span will extend from 20 to 90 minutes. If the up/down drafts balance you get a steady state thunderstorm which may last for twenty-four hours and travel a thousand miles.
The air-mass thunderstorm tends to be big and visible. Accidents occur when pilots try to fly under them. Most thunderstorm accidents occur when pilots unintentionally penetrate imbedded cells. The imbedded cell needs moisture, lifting force, and instability. Moisture is readily available in early spring. The overhead jet stream and mountains gives the required lifting action. Troughs or low-pressures aloft give the instability. The process of imbedding occurs when a wide area of wet stable air has occasional pockets of instability and lifting action. This instability is most likely to occur along a weather front.
The imbedded cell will be smaller than the air-mass cell. If the situation aloft supports instability then cells can form inside layers of stratus. Your weather briefing should cover such things as the speed of the cold front, if there is an overlying jet stream or low-pressure and if the Lifted Index is negative. Throw in irregular terrain and you have the real
likelihood of imbedded cells. Warm fronts don't usually pose a threat unless they are moving close to the speed of a cold front. A stationary front that derived from a front containing imbedded cells is likely to contain cells.
A squall line is a multiple cell storm. It is usually a nonfrontal, narrow band of fast moving thunderstorms strung out across the countryside, sometimes extending over a hundred miles.
This funnel-shaped cloud extends downward from the base with an extremely concentrated vortex that sucks up dust and debris and causes extensive ground damage.
When the winds rise above 34 kt the National Hurricane Center gives a name to a tropical storm. At 64 kts the tropical storm is called a hurricane. Such a storm is called a baguio in the Philippines, cyclone in the Indian Ocean, and typhoon in the Pacific. Out name hurricane comes from the Spanish huracan which was probably derived from the Mayan storm god Hunraken.
Narrow column of rapidly descending air is usually only about one to three miles in diameter with high velocity downdrafts that can descend to ground level creating a high velocity outflow of air. Thus, microburst wind shear effects can be both descending to 6000 fpm and horizontal variations of 80 kts. A microburst is like a truncated cone with a top diameter of one mile extending to five miles at the surface. Micro-bursts are normally wet but can be dry (rings of rising dust). The life cycle of a microburst is only 10 minutes. Do not attempt to out-climb a microburst downdraft. The best you can hope for is flight at Va to minimize structural damage while you hope to fly out.
A thunderstorm need not be mature to cause a microburst. A microburst can last as long as fifteen minutes and may not have visible precipitation. Without doppler radar or precipitation a microburst is undetectable. If you see evidence of wind shear, gusty conditions, high temperatures, a wide temperature-dew point spread and virga any two of the above are microburst probability indicators.
:It is the radiation of heat from the earth's surface that is responsible for the heat of the atmosphere above the earth. The coldness of the earth also affects the coldness of the atmosphere.
Three different lapse rates exist in the atmosphere:
The Standard one is two degrees centigrade temperature change for every one-thousand foot of change. The two degrees of change is an average decrease from the standard 15-degrees C beginning at sea level of moisture free air until in stratosphere there is no change. As the atmosphere becomes more distance from the earth it becomes cooler. This decrease in temperature is called the lapse rate. It is standardized as 3.5 degrees Fahrenheit or 2 degrees Celsius decrease per 1000' of altitude. Conditions are seldom standard. The lapse rate is a vertical temperature measure of the atmosphere.
The dry adiabatic rate is three degrees centigrade per one thousand foot of change. The dry lapse rate for density altitude computations is 5.4 degrees F per 1000-foot change in altitude. When the changes conform to this standard the pressure and density altitudes are identical. This air is not moisture free and the three degrees of cooling per one thousand feet continues until the contained moisture becomes both saturated and visible. This point of saturation and visibility is the temperature of dew point. The water vapor takes several forms such as fog, mist, dew, cloud or ice crystals when cold.
The third is the moist adiabatic rate at 1.6 degrees centigrade per one thousand foot of change. Any rise of the air after it is both saturated and visible occurs at the moist rate of 1.6 degrees C per one thousand feet. As the rising air cools it will continue to rise so long as it is cooler than its surrounding air. The water condenses out as it rises and adds latent heat due to evaporation. This is why its lapse rate is below that of dry air. As an aircraft lands it enters a region of air that can be relatively very hot when compared with air just a few feet higher. This can cause turbulence and a significant increase in density altitude. Ever wonder why the plane seems to thump down for landing on a very hot day? It will stop rising when air of equal or cooler temperature exists. Unstable air rises until it becomes still or stable. The moist adiabatic lapse rate varies with temperature depending on the amount of moisture contained. Its content varies greatly. A variation of thirty degrees could cause the lapse rate to vary a full degree per thousand feet.
Unknown Author Opinion
I have been following the thread about "How high is that cloud", and quite a few of the posters seems to have some misconceptions about lapse rate.
The *environmental lapse rate* is a measurement of the real atmosphere. The *dry adiabatic* and *wet adiabatic* lapse rates are scientific laws. Be sure that you understand the difference.
We use the laws to only estimate the temperature of an air parcel of known temperature-dew point properties, should it get lifted a specified number of feet in the *real* atmosphere.
That estimate of the bubble's temperature, only when compared to the temperature of the actual environment at that level, will help us to determine the stability. The lurid details below:
1. The real atmosphere:
Its temperature changes with height. This is the *Environmental Lapse Rate*; it can be such that the temperature is lower at higher altitudes (normal, and commonly measured in degrees per thousand feet, or similar); temperature can be higher with increases in altitude (inversion); it can even not change with changes in altitude (isothermal). The rate of change (in degrees per thousand feet) can change from one layer to another.
We know that Performance varies with atmospheres of different properties, so ICAO came up with a hypothetical *Standard* atmosphere so that we can compare. In this hypothetical atmosphere, the Temperature at Sea level is 15 degrees C, and the temperature drops off at about 1.98 (let's call it 2) degrees C per 1000 feet. The 2 degrees C per 1000 can be considered an *average* of a large number of real atmospheres, but is only occasionally representative of any particular single atmosphere, and especially not over all layers of
2. A hypothetical bubble of air: whose dew point is lower than its temperature, and which does not mix with the surrounding air:
When such a bubble is *lifted*, the pressure on it decreases and it cools. No heat is added nor released, hence *adiabatic*. Such a bubble will cool at just about 3 degrees C per 1000 feet. This is more or less constant at all pressures (hence at all levels), but remember: it will be 3 degrees per 1000 feet only as long as the dew point remains lower than the temperature. Once the temperature cools to the point of the dew point, the rules change...see 3, below.
The rate of cooling is called the "dry adiabatic lapse rate".
Note that the *Environmental lapse rate* is a *difference in the temperature* from one layer of the real atmosphere compared to another. The "dry adiabatic lapse rate" does not measure anything in the real atmosphere at all. It is a known *rate of cooling* should a parcel of air be lifted to lower pressure (or rate of warming should it be lowered to higher pressure.
3. The same hypothetical bubble of air as in number
2.: but now with the temperature equal to the dew point:
When such a bubble is lifted it tries to cool as per 2, above. But it cannot cool much below the dew point, so the dew point has to decrease also. The only way the dew point can decrease, is if some of the water vapor leaves the air, and becomes real water (cloud droplets, fog droplets). Heat is released in the process of condensing into water and that heat is used to warm the bubble somewhat.... now it cannot cool at 3 degrees per 1000, but somewhat less.
This is known as the "wet adiabatic lapse rate".
Once again, it does not measure the real atmosphere, it is a "rate of cooling" should a bubble with Temperature-equal-to-dew point start to rise to lower pressures.
How much cooling, depends on how much water condenses to release heat... Since the most moisture condenses from air that is at very high dew points, that is the sort of bubble that will cool the slowest, say about 1 degree C per 1000 feet. In very cold arctic air with dew points of minus 30, there is hardly
any more moisture, so very little heat is added in condensation, and such a bubble cools very nearly at 3 degrees per 1000, almost the same as a *dry* bubble.
In the real atmosphere, *environmental* lapse rates of greater than 3 degrees per 1000 are rare, because they are *absolutely* unstable... any small lift of a parcel would be automatically warmer than the surrounding air. If conditions are ripe to try to achieve such a steep (3-degree per 1000) *environmental* lapse rate.... hot summer afternoons.... the self-induced mixing will create a near-3-degree-per-1000 lapse rate.
What will happen is an immediate mixing... bringing cooler upper air down, and convection of the warmer lower air upward.... The *environmental* lapse rate will stabilize right around the 3-degree per 1000 rate in the surface layer.
How deep can this layer be? Depends on the strength (angle) of the sun, the length of the day and few other things, such as the type of surface.... but it will be rarely more than 6,000 feet in most areas. I am not too familiar with deserts so it may be a bit more there, but I would still estimate well short of 10,000 feet.
Above this surface layer, the *environmental* lapse rate typically is considerably less than 3 degrees per thousand feet, perhaps more like somewhere around the "standard" 2 degrees per 1000.feet.
Therefore, if we tried to lift a *bubble", say from 8000 to 10000 feet (and its dew point is lower than temperature), it will cool at 3 degree per 1000. After a 2000 foot lift it will likely be considerable cooler than the environment and will sink back (stable).
The most common scenario is a high-dew point bubble near the surface is lifted by convection. If the boundary layer's lapse rate is near 3 degrees C per 1000, the bubble will not be particularly unstable, because it will cool at 3 degrees per 1000 feet of rise, and be very nearly the same temperature as the environment.
But if the bubble has a high dew point, and the temperature cools to the point where water has to condense, *thereafter* it will cool at only about 1 degree per 1000. *NOW* it stands a good chance of being warmer than the environment and hence unstable.
Only 10% of the 100,000 annual thunderstorms are severe with hail of 3/4" and winds of 50 knots. At thunderstorm is an energy machine requiring moisture, unstable air, and lifting action which when mixed create cumulus clouds, mature thunderstorms and a dissipating phase. The cumulus state can rise at 3000 fpm. The frequency of lightning is indicative of how severe the storm is. Automated AWOS or ASOS cannot detect thunderstorms or lightning. A microburst downdraft can reach speeds of 6000 fpm.
The most dangerous icing is in the 0° to -15degrees C range since the super-cooled moisture lies in wait for the impact of an airplane to turn it into clear ice. A steady state storm is when up and down drafts are about the same. This condition produces tornadoes. A limited state storm has lost its up-drafts and is cooling off. Air mass cells are of short life and can be flown around. Frontal thunderstorms are in lines with squall lines miles ahead of the front. The uneven heating of land and water along the Florida coasts are breeding grounds for thunderstorms.
WSR 88D radar with doppler has range of 240 miles. TDWR and LLWSAS combine to allow ATC to issue wind shear and microburst alerts close to the airports. ASR-9 is a dual system for detection of traffic and precipitation. ADF are good lightning detectors is tuned to the lower frequencies. The Aviation Weather Center in Kansas City is the source of SIGMETs (WS) AIRMETs (WA) and Area Forecasts (FA).
Pilots get killed trying to beat bad weather. With so much about thunderstorms unknown and unpredictable the go/no-go decision is best always a no-go when thunderstorms exist. If trapped, turn on carb heat, tighten belts, slow to below Va, don't turn around, hold attitude level not altitude, get above -15degrees C or below zero, turn on cockpit lights, hang on.
Classification by Stages
During this stage there is usually no falling precipitation because rain is being carried upward, or is suspended by the rising air currents. Weather service uses 4000' value as a general idea when there will be significant rainfall. Every cumulus cloud is a TRW wanabe but very few make it. When a cumulus cloud is on its way to a TRW it has an updraft that may extend several thousand feet above the cloud level. The greater the vertical development the deeper will be the layer of unstable air and the greater will be the turbulence. Icing at higher levels.
During this stage precipitation begins to fall as a downdraft develops. All thunderstorms' hazards reach maximum intensity during this stage as updrafts and downdrafts create vertical wind shear and much turbulence. The severity is determined by the strength of the updraft, the presence of water droplets forming into rain which when they begin to fall through the updraft marks the beginning of the mature stage. This build-up can take as little as ten minutes.
During this stage the entire thunderstorm will become an area of downdrafts as the updrafts continually weaken. Rain will cease.
Most frequently reported pilot weather incident is a lightning strike. A lightning strike requires an electrical charge differential sufficient to cross a gap. Voltages may exceed 200M with current temperatures to 15k degrees C. We only see a small fraction of all lightning. Often there is only very small evidence of a lightning strike on an aircraft. Strikes occur most often at altitudes above 25,000 feet. About a thousand strikes on aircraft occur every year. Most do not produce significant damage, but they can.
The more we learn about thunderstorms the greater should be our respect. The instruments pilots strategy is not to fly through a thunderstorm. There are some survival tactics beginning with the preflight planning where we look at fast moving cold fronts and any surface heating. The warm, occluded and stationary fronts hide the embedded thunderstorm.
1. You can make an end run
2. You are detection equipped
3. You can delay departure
4. You can drive or buy an airplane ticket.
Accidents caused by lightning are rare. Lightning does not usually cause aircraft damage. It has, however, been known to burn holes, magnetize ferrous metal parts, possibly affect engine life, electrical systems, and damage electronic gear. Most of lightning current remains on the other surface of the aircraft by entry and exit point may show burns or holes.
Most lightning occurs within clouds. Each stroke begins when charged particles existing on ice crystals are moved by turbulence to create an area of positively charged ions. The positive ions gather at the top of a cloud and the negative electrons at the base. This causes the negative charges that exist on the earth's surface to be repelled. The effect of this is to give the earth a positive charge. With increased turbulence the fields gather strength until a leader from the clouds gives the positive ions from the ground an upward path. When the leader and the positive ions meet a sudden surge of current called the "return stroke" moves along the leader path giving a flash called lightning. The first flash often breeds others. The temperature of a flash is over 50,000 degrees F and causes instant expansion of the surrounding air with the resulting thunder sound wave. World wide there is 100 lighting flashes per second.
Lightning is a very long electrical spark. Lightning energy comes from the warm air rising into a developing cloud. Another cause is the rise and fall of graupel and hail inside a cloud the top of the cloud to accumulate a positive ion charge while the falling graupel and hail becomes negatively charged. A lighting flash occurs when the relative difference between the two charges becomes great enough. It begins with a 'leader' reaching the opposite charge. The electron difference strives to be neutral by flowing through the 'leader' at a velocity of 100 milling meters per second at upwards of 200,000 amperes. This return stroke causes the flash and boom.
Another explanation is that the negative charge of lower cloud level of graupel and hail causes the charge of the earth to become positive. Again, when the differences become great enough to break through the insulation effects of air a cloud to ground strike occurs. At first there is a slow transfer of electrons. Then a stepped leader (zigzag) goes at 60 miles per second from cloud to ground. Each zig and zag is about 200' long. As it zigs and zags it may split into multiple strokes. Each stroke is about an inch wide. When the leader reaches the ground all the surrounding higher objects send off upward streamers. When one of these streamers meets a leader it completes a circuit that proceeds upward at half the speed of light and an average of 30,000 amperes. The air in the leader tunnel reaches 60,000 F its supersonic expansion creates thunder. Each major stroke lasts a millisecond and may be followed by return strokes. Lightning occurs in flashes, bolts, sheets, ribbons, glow and balls. If you avoid thunderstorms you will avoid lightning strikes. Tucson has National Lightning Detection Network. Hundreds of sensors that use satellite linkage to continuously map activity.
If you ever get into one, don't turn back; keep going as it is the best bet for getting clear quickly. Immediately slow to Va or a few knots less. Don't sweat altitude changes. Turn off the autopilot. Air mass thunderstorms are most easily avoided. Frontal thunderstorms are much larger and stronger.
Once clear, your next decision is to head for the best weather. You may need to make a turn. The radius of your turn will be determined by your airspeed. The angle of bank will determine the load on the aircraft structure. At 110 knots a 15-degree bank has a load increase of only 4/100 of a G but the 180-degree turn has an arc of 1.3 nautical miles. At 30-degrees the G-load goes up to 1.15 while the arc is reduced to 6/10 mile. What you do very much depends on how you view the situation.
Half of all thunderstorm accidents (25 per year with 50% fatality rate)
involve VFR pilots. Because of flight direction or visibility restrictions
many thunderstorms do not appear as normally depicted. Flight into a
thunderstorm is an EMERGENCY. Apply carburetor head and pitot heat. Do not
turn. Disengage autopilot. Keep wings as level as possible and go with the
flow as concerns altitude.
Maintain visual contact with what is ahead. Keep above the clouds. Use VOR radials to confirm areas of convection since VOR radials define the regions of convective SIGMETS. Remain clear of rain shafts and virga. When flying around a storm fly upwind.
-- Item: Two out of three thunderstorm related accidents have fatalities.
--VFR flight with 5-10 mile lateral clearance. Avoidance is the first and greatest option. 20 miles for big and high ones.
--Never fly under a visible thunderstorm, under weather that may contain embedded thunderstorms, or under or near an anvil.
--Don't race a thunderstorm, go the other way. Find another airport.
--Use your radio and take the best local advice you can get.
--Slow down to maneuvering speed Va for your weight. The lighter you are the slower you go.
--Manage the cockpit, passengers and articles tied down.
--Don't try to turn. Keep wings level and accept altitude changes.
--Attempting to maintain altitude is a most likely source of structural failure.
--Pitot heat, carburetor heat, and cockpit lights on.
--Flight below cumulus will be bumpy but you can see the dark ones and rain to be avoided.
--You can't judge a thunderstorm by external appearance.
Once you have decided to fly into a possible cumulus concentrate on aircraft control. Fly by attitude not altitude. Accept any altitude changes and advise ATC of this. Keep your wings level and don't turn back since this turn may cause the structural limits of the aircraft to be exceeded. Hold your heading as the shortest possible route out of the situation.
--Seven out of ten T-storm accidents have fatalities.
--Wind velocity at 10,000' gives rough estimate of thunderstorm movement.
--50-100 earth strikes per second year round from 1800-1900 existing average of thunderstorms occurring at any moment.
--Most lighting is inside of clouds. Next in frequency is cloud to ground. Cloud to cloud and cloud to air are rare.
--Lightning is multiple strokes lasting a half-second with pauses. Width of a finger but can be miles long.
--Florida is thunderstorm center with 25-40 ground strikes per square mile.
--Lightning kills 100 and injures 250 every year more than the combined totals of tornadoes and hurricanes.
--Fewer thunderstorms develop in an area during the winter due to low freezing levels.
--1.5% of all storms contain severe wind shear.
--The more frequent the lightning, the more severe the thunderstorm
--Increasing frequency of lightning means a growing thunderstorm
--Lighting along a large part of the horizon indicates a squall line.
--Don't takeoff or land into a thunderstorm
--Don't fly into or under a thunderstorm
--Don't try to fly around a large thunderstorm
--Avoid by 20 miles identified as severe
--Only 8% of level three storms contain severe turbulence.
Essentials for a thunderstorm are:
1. Unstable air
3. Uplifting force
The stability of the air depends upon temperature differentials. Temperature has a standard lapse rate of cooling of 3 degrees Celsius per thousand feet. When the lapse rate is less, the air mass is relatively stable. When the lapse rate is more, the air mass is unstable and rising. Temperatures are seldom standard. Once air begins to rise it will continue to the tropopause. When this rising air reaches the dew point the clouds will form a base for what comes next. The lower the dew point the lower the cloud base. The thunderstorm arises, literally, when a thermal kick occurs. Heat, a front or a mountain can cause this kick. Only a slight kick is needed to start the lift rolling. Never fly between a mountain ridge and the base of a building thunderstorm. Radar will show a thunderstorm but you must ask for it.
Avoid any thunderstorm you can see. They usually build up in the late morning and last through evening. The best avoidance distant is as far as you can get. Should an encounter occur, Fly at Va, keep the wings level, ignore altitude changes, hold heading and pitch attitude. Panic is your worst enemy.
Only about five percent of all thunderstorms at a given moment will damage
Only one out of three thousand thunderstorm encounters will result in a fatal accident.
1. Gust intensity
2. Rainfall intensity
3. Altitude minimum
4. Volume (size/height)
5. Echo strength
Thunderstorm (Minimum Basic Knowledge)
--Air with high moisture content
The latent heat released by condensation of existing water moisture increases the buoyancy of the lifting air column until it becomes self sustaining. Byproducts of this process are clouds, kinds of precipitation, and vertical winds capable of destroying aircraft.
Cumulous clouds can be numerous but only a few get a dominating updraft leading to the mature dangerous
stage. As the cloud rises the moisture droplet size increases.
When the droplets cannot be lifted they will fall as rain or hail depending on temperature.
A limited state mature storm may last only a few minutes before self-destructing via downdrafts which cut
off the process by cooling.
-- Steady state thunderstorm cells can last for 24 hours if the up and down drafts continue to exist in balance.
Maturity means large hail, heavy rain and extreme turbulence.
When all the water droplets and hail have fallen from the storm the dissipating stage is complete.
--Avoid all thunderstorms
--Never get closer than five miles
--Hail and violent turbulence extends to 20 miles
--Avoid flying beneath thunderstorms
--Reduce speed at first sign of turbulence
--Make an early 180 degree turn
More on Thunderstorms and Avoidance
--Monitor en route AWOS, ASOS and 122.0 (Flight Watch)
--File IFR or at least use VFR advisories
--Listen to HIWAS when available on the VORs (Black dot)
--Keep visual contact and separation for cumulus clouds (20 miles minimum)
--Don't fly in or near convective weather. Having done it before and escaped is the worst lesson possible.
--Get the convective outlook at www.spc.noaa.gov/products/outlook/day1otlk.htm. (seldom wrong)
--Get the convective SIGMETS for existing storms on HIWAS or 122.0
--Dew points in above 60F/15C are a sure sign of trouble.
--The southeastern corner of a trough is most dangerous area.
--A hook or a bow means that tornadoes are in the area. Negative numbers 3 to 6 in lifted index are bad news.
--Fly very early in the morning and be on the ground by 10 am.
--Survival in a thunderstorm is more luck than skill.
--Tighten seat belts, stow loose items and turn up lighting.
--Know your appropriate Va and how to get to it quickly. NO flaps!
--Slow to Va (Vref) for gross weight …lighter needs slower but as much above stall as you can take.
--Fly attitude not altitude…accept altitude excursions.
--Maintain heading…do not turn…likely excess G force.
--Maintain control and think positively.
--Communicate your situation and position.
--The larger the storm the further it will throw water, hail, and turbulence.
--Don't fly beneath a thunderstorm
--Don't try to beat a thunderstorm to the airport.
--Know how to use and interpret your lightning detection equipment
--Worst storm for aircraft is squall line
--Gust front winds cover 20 miles, speed range 100 knots, wind shear, mamma and roll clouds
--Micro-bursts 1 to 4 mile diameter, downdrafts over 80 knots, 75 knot horizontal winds, 2-5 minute life.
--Microburst can occur in clear air and may be 'dry'.
--Up and Down drafts required for maturity by internal orographic lifting and heat exchange
--Tornado caused by rotation and acceleration
--Rising moisture freezes and falls as hail as green area below anvil top.
--All forms of ice occur, accumulation instantaneous, use alternate air and carburetor heat. 6-8000' worst area
--Lightning hazard is blindness, loss of electrical, skin damage. Worst from + 5-degrees C.
--20-mile minimum avoidance distance.
--G.A. aircraft have no published Vb (turbulence penetration speed) Use up to top of green arc. Slower better.
--Accident records show that inadvertent stall (too slow) not structural failure greatest hazard.
--If it looks dangerous, it is.
--Spheric Interpretation a false reading called radial spread causes display of strong storms beyond 200 mile range.
Flying with Thunderstorms
--You can learn about thunderstorms by watching on the ground.
--They arrive from the south and wind velocity is indicative of strength.
--The first wind gust is a clockwise shift and comes from a downdraft within the storm
--G.A. aircraft structure is exceeded when gusts exceed 18 knots.
--Loss of control by pilot is primary cause of structural failure.
--Maintain direction only, ignore altitude and keep wings level
--Greatest turbulence is near edge of storm's rainfall toward the side in which it is moving.
--Given a choice, fly everywhere but West.
--Half of thunderstorm accidents occur on VFR flights
--Recently on a commercial flight at 39,000 feet we had moderate chop when 88 miles from thunderstorms,
--Severe thunderstorms can develop very quickly before advisories can warn pilots.
--In VFR and within five miles of thunderstorm conditions can destroy an aircraft.
--Thunderstorm PIREPS lose their validity almost immediately.
--The twenty-mile guideline for VFR avoidance is a minimum well-used on IFR flights as well.
--Once in a thunderstorm your only option is to continue straight ahead at below Va airspeed. Gear down.
--Va is the maximum speed at which the structural limit load can be survived without structural damage.
--If the limit load is exceeded by 1.5 times the limit for three seconds it may bend but not break.
-- Beyond the three seconds you are at the ultimate limit load place where things come apart.
--The stall is a structural protective system in which the aircraft will stall before breaking.
--Va is for a positive G loading. The Va for a negative loading occurs at a higher speed. Thus a thunderstorm consisting of both up and down drafts should be flown below Va to avoid exceeding the negative limits.
--Thunder storm sequence is cumulus into mature into dissipating
--Thunderstorm wind categories are downdrafts, macrobursts (downbursts) and micro-bursts
--Columns of descending and outward flowing (Up to 18 miles) air below 720 fpm are called downdrafts.
--Columns of descending and outward flowing are above 720 fpm are called a downdraft
--Columns of descending and outward flowing inside three mile circle above 720 fpm are called micro-bursts.
-- These columns can be wet or dry.
--Many accidents but no fatalities recorded from dry micro-bursts.
--VIRGA is Variable Intensity Rain Gradient Aloft with up to 65 knot rain/air falling that doesn't hit the ground
--Thunderstorm windshear is a pulse-break-pulse event up to 212 knots
--You have a 98 percent chance of not getting a thunderstorm wind shear underneath
Tornadoes begin as horizontal spinning air formed from the updrafts of thunderstorms
--The updraft tends to tilt the spinning air with one end reaching the ground
--88 percent of tornadoes are weak causing 5 percent of deaths. Life one to ten minutes, winds 110 mph
--11 percent of tornadoes are strong causing 30 percent of deaths. Life over 20 minutes, winds 110 to 205 mph
--Once percent of tornadoes are violent causing 70 percent of deaths. Life exceeds one hour, winds over 205
--No place is safe from tornadoes
--Wind velocity not pressure differences causes damage
--Opening windows does little good. Get to a safe place like in a bathtub.
--Get to a shelter. An automobile is not a good shelter.
--Best shelter is inside a strong building
--On average one person is killed for every 17 tornadoes.
-- One person is usually injured for every one of the 1500 annual tornadoes
--On average tornadoes move southwest to northeast.
--Average speed is 30 mph but have reached 70 mph
--Most tornadoes occur from 3 p.m. to 9 p.m.
--Rotation speeds reach 250 mph
--Tornadoes can occur at any time of the year.
--Most tornadoes occur east of the Rockies during the spring and summer
--Southern states have tornadoes March through May
--Northern states have tornadoes late spring and summer
--A cloud to ground strike begins when a cloud 'leader' attracts a charge from the ground making the flash
--'Heat lightning' is term used for lightning too far away to hear the resulting thunder.
--Give time lapse of 30 minutes after last clap of thunder before going outside.
--Lightning kills 80 and injures 300 every year on average
--A person struck by lightning has no electrical charge
--There are 20 million strikes every year
--Rain is not needed to have a lightning strike especially in the west
--You are safer inside a car not touching metal than outside.
--One strike could light a bulb for three months
--Air near is lightning strike is 50,000 degrees Fahrenheit
--Strikes hit humans during the summer in the afternoon and early evening
--Lightning is a common cause of forest fires
--Divide the number of seconds from lightning flash to thunder by five to get distance in miles.
--Rain is a good indicator of thunderstorm intensity because it is a good reflector of radar transmissions.
--Raindrops increase in size the further aloft they go in an updraft.
--Storm strength is proportional to the velocity of vertical air currents and the height they reach.
--Lightning is not necessarily a component of thunderstorm rain.
--National Convective Weather Forecast is most accurate for long-lived mature multi-storm line storms.
Ice Ain't Nice
--Climbing out of ice is best choice if possible.
--1/2 inch of ice increases drag over 50 percent
--Cold + wet = ice
--Ice is either rime, clear or mixed
--Clear ice is slow freezing of large water drops between 0 and -10C. Weight 62 pounds per cubic foot.
--Rime ice is rough and crusty from small supercooled drops. Affects airfoil in stratus clouds 0 to -40C.
--Impact ice effects on induction, windshield, static ports and pitot tubes are worse than that on wings.
--Know when pitot is on and have plan if it fails.
--Best icing information is from PIREPS and visual sighting.
--Wing struts and corners of windshield are good places to look for ice.
--For every little bit on you wings there will be much more on your tail.
--Terms of accumulation are trace, light, moderate and severe. (PTS test question)
--Do not attempt to fly with frost on the wings. Do not hose it off…will make even worse.
Snow Rhymes with No
--An outlook briefing is one way to adjust your disappointment level sooner rather than later
--Forecasts for marginal weather makes decisions more difficult
--Accidents most often occur in flight where, "Chances of occasional marginal VFR weather" are forecast.
--VFR cross-country flight in winter must always be planned with multiple alternatives at any point.
--FSS predictions of ice is automatic any time temperature is below 10 degrees.
--A PIREP is valid only for the moment given.
--Any form of precipitation in winter is a valid reason not to fly.
--A cold airplane will get ice where only rain exists.
--Occluded weather fronts are the worst
--Do not bet your aircraft performance against airfoil contamination
--A warm airplane will turn snow into ice
--Impact snow that sticks to leading edge surfaces will reduce lift by 30 percent
--Precipitation taken to freezing levels can freeze into position flight controls and engine controls.
--Any airfoil contamination will lower the critical angle of attack
--Clouds are cold when it snows.
--Snow can clog up many things on an aircraft.
--The attitude to have is to continue work at an emergency problem after the checklist is completed. .
--Teach students to use carb heat before you need it and not as a deicing measure.
--Flight in conditions that are conducive to icing requires you to apply full heat every few minutes.
--If you have a carb temp gauge utilize partial carburetor heat to keep the carb throat temperature at a level high enough to prevent induction icing.
Climbing to Escape Ice
--Climbing to escape ice means that you must climb through the worst ice on the way.
--Your climb rate may not be sufficient to go all the way through.
---The most reliable icing information is via PIREP
---Climb to get above icing if you are capable of climbing through the heaviest icing.
---Hypoxia is a variable to each individual and to each exposure.
---What happens at 22,000 is far more serious than at 16,000
---The mid-altitudes give you off-airway direct routing not otherwise available.
---To avoid IFR STAR arrivals, cancel and go VFR.
Thunderstorms in Brief
---Don’t fly where you can’t give thunderstorms 20 mile clearance.
---The worst thunderstorms are most southerly or exceeding speed of19 knots
---Look out when the surface dewpoint is 50 degrees +and temperature is 30 degrees is the spread
---Radar is an avoidance not a penetration aid
---Check DUAT or DUATS for Severe Warning Section or FSS for AC Notes
---Winds from the southwest at 18000 feet carry storms
---Plan to fly in the morning before heat of the day arrives
---Do not depart if storm is closer than twenty miles.
Return to whittsflying Home Page
Continued on 5.538 Weather Flying Decisions