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Weather Detection and Reporting
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Real Time Weather; ...Forecast Reliability; ...Satellite Weather; ...Radiosonde (RADAT); ...Weather Radar; ...AWOS; ...ASOS (newest); ...Convective SIGMETS; ...Antiquated Automated Weather; ...Phone and Radio; Ceiling; Atmospheric Properties; ATC Radar Facilities and Weather; Weather Service Radar; Weather and Radar Processors (WARP); Internet AWOS; Bay Area Weather; ...Local Conditions4; ...Glossary; ...
Real Time Weather
In 1985 Kansas had 3200 weather observations in 1995 there will be 86,600. The Aviation Weather Products Generator (AWPG) will brief pilots in the air with an accuracy of 5-10 miles and 5 minutes. 1000 airliners will be transmitting continuous weather data as they criss-cross the U.S. Airport controllers will have a three dimensional view of the weather and the approach to the runway. Virtual reality is here.
The first GOES satellite went up in 1975, six more have flown since. Two operate, east and west, most of the time. They give early warning and tracking for hurricanes and severe weather.
Geostationary Orbiting Environmental Satellite (GOES)
--Uses infrared photo to get cloud top temperatures. Darker color shows colder temperatures.
--Shows precipitation not clouds.
--Radar Summary Reports
--Radar images are summarized. May be vague but verify Radar Composite.
For 12 hours good weather more correct than IFR
Poor weather in 3-4 hours at 80% accuracy
Distinct systems improve accuracy of forecast with tendency to under estimate severity
Cold front weather most difficult to forecast
Surface visibility forecast worse than ceiling
Cold front passage + 2 hours
Warm front passage + 5 hours
Warm front ceilings + 200' + 4 hours
Thunderstorms 1-2 hours with radar
Rain/snow + 5 hours
Weather briefing number
1-866-766-0820 for distant FSS
12-Hour Icing Forecast
Changing to the Aviation Routine Weather Report (METAR) and Terminal Aerodrome
Forecast (TAF) formats puts U.S. in step with rest of world in terms of
weather format. In 1993 250 landing rights airports of the U. S. converted to
the METAR code for international purposes. The rest of the world changed from
the old METAR to the 'new'. By 1996 the U.S. will be completely METAR.
Attempt to demystify the new METAR/TAF weather formats at:
Images reveal temperatures (height) coverage, movement, fronts. All images are dated.
--Geostationary Operational Environmental Satellites (GOES) at 22,380 miles high. Picture distorted by curvature. --One large fixed area. Putting images into a film loop gives motion.
--GOES 8 is eastern US and GOES 9 is western --US. Visual images are photographic in appearance.
--Weather, clouds and surface are judged by ability to reflect light.
--Some interpretative conflicts exist and no cloud height information.
--Infra-red images are based upon cloud temperatures (heights).
--Thunderstorms are apparent as the brightest and coldest. Works as well at night as day.
--Water Vapor images show water vapor in levels of brightness.
Polar Orbiter Environmental Satellites (POES) at 3-500 miles. 900 mile wide strip-map.
Rawinsonde DATa are upper air soundings via balloon. More than 1000 points that take soundings once at noon and again at midnight zulu time.
Type 1 called wind racks (Rawinsonde
Every 6 minutes gives wind direction and velocity
Type 2 Rags
Gives temperature and moisture and presented on constant pressure charts.
Balloons are soon to be replaced by wind profilers that detect winds by means of doppler radar and acoustic sounding. The profiler will every six minutes will take a variety of samples that will give winds aloft at 72 altitudes up to 53,000 feet. The computations are accurate to two knots. This system is not moisture dependent. Low level jet streams are checked to determine existence, extent of layers and velocity of wind shear.
Temperatures are measured by acoustic blasts at 850 hertz. The speed of the sound is measured by doppler radar as it varies in speed due to temperature differences. This works up to 18,000 feet. Balloons are to be used above this altitude.
121 Weather Radars total in the U.S.
Present system uses 1950's era radar, which is down 20% of time. 40 newer radars have lower false alarm rate of bad weather The WSF-88D has 8 times the resolution, twice the range and 16 times the weather sensitivity. Predicting will be possible.
ARTCC radars do display precipitation and can on request give a pilot real-time (right now) information. Radar returns are known as Levels I, II, III, and IV. The National Weather Service uses six levels of thunderstorm intensity. ARTCC radar controllers have three weather display keys: WX-1, WX-2, and WX-3. WX-1 gives diagonal slashes on the screen to show moderate precipitation. WX-2 gives H Hs to show heavier areas and WX-3 shows both. The controllers are required to call every H as a Level VI thunderstorm. A pilot in need can request the controller to use the WX keys for assistance in weather avoidance. ARTCC will not volunteer this help you must ask for it.
New doppler radars (vary frequency much the way a train whistle does when passing) in the UHF serves as a wind profiling radar in combination with an acoustic transmitter enables the measurement of a temperature sounding. The maximum height of the doppler radar capability is greater than the acoustic pulse because the acoustic pulse is moved out of the radar beam.
The new weather radar will give coverage to 10,000' from 175 sites and no gaps east of Cheyenne. 40% of the radar weather coverage will be in new areas. System works by showing air motion and will be given to other ATC facilities. Some day into the cockpit? Another system will give 45 airports severe storm information and can be scan-specific to most important runways. Accuracy will vary from 60 to 80%.
New systems are going to be able to derive (predict) data. Present system has more data than can be processed, interpreted or distributed. Record the altitude of each )degreeC isotherm. Green on color charts indicate dewpoint spread of less than 5°. Icing exists where shaded area cut by 0 degrees to -10 degrees isotherms. 500 millibar winds (128,000') are usually emphasized because they are removed from earth surface influences.
Icing forecasts take over when there are no PIREPS given. When you give weather PIREPS, so so every 15 minutes so they can be charted as they change. There is now a chart being created based only on PIREPS.
When asking radar for weather you must first find out if they have weather
detection capability. The radio procedure is to say, "Give me the setup
of all Level-2 and above weather and vectors around it."
SLC 1400 RADAT 70 M 030 066 165 /3
SID UTC rh rh y y y
to mid y Y's in 100's Additional
Station relative of feet of isotherms
identifier humidity 0° isotherms crossed
Automated weather observation system AWOS has 160 sites in operation to be replace with Automated surface observation system of ASOS. Neither has the flexibility of a human observer. Improvements allow automation of cloud heights, coverage, weather, and visibility. The originals were developed before the 1980s and will not be fully in place until after the year 2000. Something seems wrong that such a vital system should be so delayed. Rapidly changing weather will be unreliable when reported by an AWOS. Probably the biggest difference is that ASOS is capable of discriminating between types of precipitation. It also has lightning detection. AWOS cannot do those things
--ATIS, AWOS, ASOS
--ATIS during the last 15-minutes of the hour.. More often means significant weather.
Sequence: (Always the same)
1) Report identifier and time
2) Wind and velocity (You must picture the extent of crosswind for runway)
3) Visibility and sky cover. Sets VFR, MVFR or IFR conditions.
4) Temperature and dew point. Helps you determine freezing level and icing probability.
5) Altimeter setting. Gives weather trend.
AWOS is fully automated with sensors that send information to computer
which voices information over discrete frequency. AWOS was the basic system to
be followed by the ASOS's greater sophistication. Three versions give varied
weather information of varied reliability and dependability. AWOS-A only
reports altimeter setting.
AWOS-1 has altimeter, wind, temperature, dew point, and density altitude. AWOS-2 adds visibility.
AWOS-3 adds cloud and ceiling.
AWOS-3P adds lighting up to 30nm distant, in vicinity or at airport.
AWOS-3P/T will include thunderstorms. Installations by NOTAM.
AWOS 4 Additionally gives precipitation and storms
KEY TO AWOS
HTM SA 1755 AWOS MGO OVC 1V 36/34/2015G25/990/ PO10/VSBY 1/2V2 WND 17V23/WEA: R--F
If you can't interpret this refer to the AIM. Study !!
With a tower in operation an ASOS does not change continuously. It updates every hour as does the ATIS.1700 ASOS (Automated Surface Observation Systems) are to be installed with improved information and accuracy. Via automated radio we will receive altimeter settings, wind speed and direction, temperature/dew point, density altitude, types and intensity of precipitation, cloud height, visibility, pressure changes and tendencies, and wind shifts. Runway advisories. ASOS data is a minute-by-minute evaluation of sky, visibility, and weather as would be a complete surface aviation observation.
Will replace 250 weather observers and 300 FSSs or towers. 118 ASOS were installed in 1992. Performance is Equal to daytime observers and superior at night. Makes continuous radio and phone data available. Modem to FAA and NWS networks. The systems use electronic sensors and computer processing. Some facilities provide precipitation, and restrictions to visibility.
The FAA automated surface observing system (ASOS) will be located at 900 airports of which 26 will have lightning detectors, 400 will be totally automatic, 250 will be at part-time towered airports, 57 will have human assistance and 78 will have augmented sky condition information.
ASOS is most reliable when giving wind speed, direction and altimeter settings. Most errors occur in cloud height, sky cover, visibility, and precipitation type. ASOS uses averages over time for most readings. Averages can cause errors especially in rapidly changing conditions. Only be listening over at least ten minutes can you hope to pick up on any discrepancies.
ASOS uses average values while the observer uses spot values. ASOS sees clouds only straight up. Visibility is touchdown zone visibility. ASOS is more capable and flexible that AWOS. ASOS has eight sensors which sample once a minute ASOS cannot detect thunderstorms, differentiate hail, ice crystals, ice pellets, blowing obstructions and drizzle from freezing drizzle.
Automatic report of:
--Sky condition below 12,000' overcast, variable, etc. with laser beam ceilometer. Laser check every 1/2 minute for thirty minutes. Clouds can be measured in three layers. Computer generated data is broadcast as scattered, broken, or overcast.
--Visibility up to 10+ miles variable...etc.
--Type/intensity of rain, snow Fog or haze
--Sea level pressure in Hectopascals (hPa) and altimeter setting
Changes and direction of change hPa is equal to millibar (mb)
--Temperature in Fahrenheit, dew point,
-- wind speed in knots and direction (TRUE to nearer 10 degrees)
and wind character as gusts, shift, peak, etc.
--Computerized voice with changes every minute, thresholds by hour
and 15 minutes. Specials available.
--Allows manual insertion such as thunderstorm data.
Observer supplemental may not be transmitted by ASOS
ASOS the first system gave only altimeter setting
ASOS-2 gave wind, temperature, dewpoint and density altitude
ASOS-3 gave remarks on wind/ceiling variability
AO2 code senses type of precipitation and amount
AO2A the A means an observer has added information forwarded to the weather system than may not be transmitted to the pilot via radio. The observer uses a fixed time averaging technique.
During daylight the ASOS will be used to validate area (FA)and terminal (FT) forecasts. Lightning detectors are currently in use.
KEY TO ASOS_________________________________________________________________________
HTM RS 1755 AO2A M19V OVC 1R--F125/36/34/2116G24/990/ R29LVR10V50 CIG 16V22 TWR VSBY 2 PK WND 2032/1732 PRESFR ZRNO $
If you can't interpret this refer to AIM for chart. STUDY!!
Convective SIGMETs (WST)
Any Convective SIGMET for the area and time of a light aircraft is ample reason for a no-go decision. Getting data via the internet does not substitute for the formal preflight weather briefing by visit or phone call to an FSS or the use of DUATS 80% of the rain East of the Rockies falls from thunderstorms during the summer. Most of this comes from large groups of thunderstorms hundreds of miles across, known as mesoscale connective complexes or MCCs. In 1993 MCCs broke all previous records for rainfall.
An MCC is a mix of weather comprising all factors of warm and cold fronts. The weather reflects such a mix of conditions that the elements feed on themselves without requiring the temperature changes of daytime. MCCs generate low-level jet speed wind conditions. Only movement into cooling conditions will cause the MCC to die.
You will not find MCCs mentioned in most weather texts. MCCs are mentioned only in the last year or so in the synopsis part of area forecasts from the Aviation Weather Center. Mention of MCC in an area forecast is sufficient to make a general aviation plane to remain on the ground.
Antiquated Automated Weather
Five systems are currently in use. Older (40 years older) ones are being upgraded or replaced with more capabilities. There information may be distributed by radio, phone or computer. Automation eliminates the much needed human factor required to fill in the blanks.
A potentially dangerous situation can and will be missed by the automated systems. Automated reports can be misleading. It is very useful at uncontrolled remote airports but its shortcomings should make a pilot cautious.
AUTO-B is automatic coded weather in CA, TX, UT, and AX. It is capable of giving sky conditions, visibility and precipitation.
Four in existence.
California's at Sandberg (SDB)
Backscatter (pollution) visibility reported in even miles as BV5
RAMOS is remote automatic meteorological observation station
Like AMOS but gives pressure changes every three hours, max/min temperatures and 24-hr precipitation
AMOS is automatic meteorological observation station 90 of which exist in the nation (Blue Canyon, near Tahoe)
ASOS Automated surface observation system 1700 to be installed
APAWS Automatic weather readouts from commercial aircraft every 7 minutes nation wide.
Phone and Radio
Automated FSS (AFSS)
Taped route Wx information
National Weather Service 5 day forecasts
Tower, airport manager, FBO, local radio station
ASOS is telephone accessible
If Sectional frequency box has small solid rectangle in one corner it will have continuous radio weather
METARs are Aviation Routine Weather Reports made hourly.
TAFs are Terminal Aerodrome Forecasts
FC vs FC+
Difference has to do with touching the ground.
FC is a funnel clout
FC+ is a tornado
The heights above the earth's surface of the lowest layer of clouds or obscuring phenomena that is reported as 'broken,' 'overcast,' or 'obscuration,' and not classified as 'thin,' or 'partial.'
The atmosphere has certain properties that can be measured (or calculated). Namely temperature, pressure, and density. These properties change with altitude.
Up to the tropopause, temperature, for example, tends to decrease with altitude. This is because the sun heats the surface and the surface heats the mass of air closest to the surface. The increase in temperature causes the air to expand, which means it becomes less dense. Less dense means more buoyant. The warmed air tends to float upward. As it floats upward, it moves to an area where pressure is lower, so it expands further. As a gas expands, its temperature drops. Eventually it cools to the termperature of the surrounding airmass and rises no further.
The ("actual") lapse rate is the rate temperature decreases with altitude. When the lapse rate is low, the warm surface air will tend to be less bouyant and the airmass is said to be stable. When the rate is high, the airmass is going to tend to shoot up, possibly overshooting it's area of neutral boyancy. This is said to be an unstable airmass.
Sometimes you get an airmass where the temperature is warmer at higher altitude. This is called an "inversion".
So, the atmosphere has properties that change with altitude, but those properties also change with weather conditions. You can be in a high pressure area or you can be in a low pressure area. Wind is caused by pressure differences. Air is pushed from high pressure to low pressure, but because the earth is rotating, the air gets deflected to the side ("Coriolis force") and winds up traveling parallel to the lines of pressure rather than perpendicular as one would expect.
Because of all this variability of the properties of the atmosphere, the International Standards Organization got together and *defined* a standard atmosphere. The standard atmosphere has a temperature of 15C and pressure 29.92"hg at sea level. The lapse rate is is about 2 degrees C and 1"hg per thousand feet.
We use pressure to give us a proxy for altitude. The altimeter (set to 29.92"hg) is a glorified barometer, but it's calibrated to read "altitude". This "altitude" is what corresponds to a given pressure in the table the ISO people use for the Standard Atmosphere. I.E. your pressure altitude.
Above 18000' in the U.S. (other countries are different), this works out ok because the pressure differences aren't so great that a plane would risk hitting terrain trusting the altimeter, and everyone is using the same setting.
At lower altitudes, it's a potential problem, so we have an altimeter setting. You dial in the number that causes the altimeter to read the real altitude (above sea level, which is also an idealized value) at the surface.
Say you're in an area of low pressure. Your altimeter will read a higher altitude than what you're really at. Let's say it reads 1000' above your real altitude. What you do is dial in 28.92 and shift the entire scale downward. The altimeter setting is what the sea level pressure would to be to shift the scale such that it reads the local altitude at the pressure of the weather station (got that?).
Of course, the decrease in pressure with altitude won't necessarily match what the calibration of the altimeter says, but it's good enough for our purposes. Most accurate at the ground, with decreasing accuracy as altitude increases, but this is okay since everyone is using the same setting and it gives us a better value for obstacle clearance. In IFR flight around non-mountainous areas, the minimum enroute altitude is 1000' above the surface. This is in part to cover the altimeter error (and also to allow the pilot slight deviations).
Aircraft performance depends on the density of the air. That's (effectively) number of molecules per unit of volume. This depends on temperature and pressure. Instead of reading density directly, we use the concept of "density altitude" which is similar to "pressure altitude": it's the altitude you'd have to be at in a standard atmosphere to have the prevailing density.
Given an air pressure (read as a pressure altitude) and a temperature, you can compute the density altitude. It's not a trivial formula, so I just use my E6B to crank out the numbers as needed.
To solve a typical performance problem, you need the temperature, pressure and altitude of the station. Let's say pressure is 28.82"hg and the altitude is 250' above sea level. Without correcting the altimeter, you'd have an altitude of 1000' (pressure altitude).
In a standard atmosphere, the pressure should be 29.67 (29.92 at sea level - 0.25 for the elevation), but if you dial in 29.07 (28.82 current pressure + 0.25 for the 250' elevation) you get a reading of 250' at the current elevation. 29.07 would be the projected sea level.
Now that you know the pressure altitude, you can use that with the temperature to compute density altitude for performance. Not that some performance charts use a table with rows for pressure altitude and columns for temperature. This effectively gives you your density altitude without having to calculate it.
Facilities and Weather
--Do not rely on ATC RADAR for weather information
--The pilot is responsible for aircraft safety and weather avoidance
--If there is a conflict in what you see and know and ATC's information, get on the ground.
--ATC radar is unreliable when it comes to presenting weather.
--An untrained controller may fly you into trouble
Weather Service Radar
--New WSR-88D doppler weather surveillance radar is excellent and detection weather and estimating rainfall
--Doppler detects speed and direction even spin motion differences
--160 WSR-88D radars will form an integrated network covering U.S. and island territories
Weather and Radar
--ATC to reroute traffic to avoid weather
--Real-time weather in color w/precipitation ate three different altitudes.
--ATC gets accurate localized precipitation and weather effects.
AWOS Weather Advisor internet sites:
40N in PA
Bay Area Weather
---Satellite and computer technology have given us new knowledge about why our weather is as it is.
---What and why what is happening now is the weather and every valley is its own microclimate
---Every valley modifies its weather to the terrain of the area
---As a pilot you should become weather sensitive to your immediate airport conditions
---Experience enables a pilot to more accurately predict 'his' weather from 'the' weather
Fog of a Different Kind
---When the earth is wet the sun causes radiation fog
---When the earth is hot it draws the winds from the sea to cause advection fog
---Both kinds of fog provide Bay Area air conditioning of different kinds.
---It is not common knowledge that it is the salt in the air that triggers the formation of fog.
---The geography consists of mountain range deviators, barriers and leaks
---The Bay area is a contact point between the climatic forces of sea and land
---The coastal range is a series of channels for movements of winds and associated weather.
---Winds carry moisture through the Golden Gate spreading coastal weather along the shorelines.
---The rainfall on one valley makes the valley over the hill that much dryer
---Average weight is 14.7 pounds of pressure per square inch of the earths surface
---Warm air weighs less than does a corresponding column of cold air
---Cold air causes high pressure areas of air while warm air causes low pressure areas.
---Temperature is not alone in causing high or low pressures but it is primary in Bay Area weather
---The differences in temperatures are caused by air movement to equalize its temperatures
---The differences in air pressure are also a cause of its movement to equalize its pressures
---Dry air rises, expands and cools 5.5 degrees F. per thousand feet of rise.
---Falling air reverses the change becoming compressed and warmer by 5.5 degrees F per K of descent
---Warm air holds more moisture as invisible vapor but when cooled the vapor reaches the dew point
---At the dew point temperature is where the water vapor becomes visible
---The earths rotation is counter clockwise, the North the friction causes winds to curve to the right
The Four Seasons Differ
---The westerly winds blow on to the California coast more intensively in March, April and May
---The Central Valley heats up, air rises and low pressure reigns as an onshore pressure gradient.
---The sucking effect pulls the high pressure cool ocean air into the Gate first, second any cut.
---The equatorial heat moves toward the Arctic where cooling it causes the Pacific high
---The high spinning right comes down the coast and inland where possible like the Bay Area
---This wind drives and rides ocean currents along the coast lifting deeper and colder water
---It is this lifted cold water than air-conditions the coast, initially invisible vapor, it cools into fog
---The wind-driven wave spume that contains the salt particles needed for moisture to make fog
---The coastal fog may be a wisp to many miles wide and 100 to 3000 thick
---Wind, sun, and terrain causes fog to move from off-shore to the Central Valley and back
---Usually takes four days coming in and four days going out and then in and out again and again
---This is the advection fog that allows SVFR below with great visibility and blue skies above
---Advection fog is a low stratus cloud, just as a high stratus cloud is a high advection fog
---Incoming cold tides at the Golden Gate causes a fog that the next outgoing tide will erase
---Advection fog gives way to sunlight and reappears at sunset. Very predictable changes.
---One of the most memorable movies I have ever seen is one showing a ten-second time lapse of fog coming into San Francisco Airport.
---Other larger weather forces affect the cycle of days of fog followed by days of sun
---Of the four jet streams only the Polar Jet Stream has an effect on continental U.S. weather
---The Polar Jet Stream shifts and loops up and down the U.S. high in winter and low in summer
---Jet stream loops past Bay Area with troughs changing things enough to give clear weather
---The stream can cause the fog layer to be trapped below warm air called an inversion = smog.
---It is not until the cool air flow through the Gate below the inversion is lifted enough to stay high
---The summer incoming fog is higher than that of spring as it forms at the base of the inversion
---Learn to distinguish between wet fog and dry fog, the wet fog is summer water for plants
---Jet stream ridge brings clear days and the Diablo warm winds overland entering the Bay
---This is fire weather in the East Bay and beach weather along the coast. 1923, 1928, 1991
---A stationary jet stream may give days of clear or fog depending on the prevailing winds
---California fishing and agriculture cycle according to the jet stream influence on climate
---The micro-climates of the Bay Area will continue to have their differences to a lesser degree
SFO Summer in the Fall
---Bay Area has at least ten different gaps or passes through which the ocean winds can funnel
---Summer comes in the fall September and October are hot and November warmer than April
---Fall sun loses power and effect on the ocean so only shoreline fog. while temperatures rise
---Fog changes to smog that moves as a layer over the bay and occasionally over the hills
---Without the Pacific High weather moves in from Mexico and planes land to the south.
Rains Begin in Winter
---Thunderstorms and cloud formations arrive with unpredictable conditions as days grow shorter
---Winter clouds are warnings to the pilot so you should learn classification and characteristics
---There are nine levels of clouds, and being on cloud nine means being on top.
---Level layer of clouds at same temperature
---Blown into hill sides forms thicker layer until over the top but clear below deck
---On lifting may bubble up as nimbostratus
----Nimbostratus close to surface-6k
---Once 4k thick will give continuous rain for hours from dark mass of clouds
---Flat bottom and puffy above
---Top of rising column of air
---Cumulus congestus surface-50k
---Exploding all over the top
---Can out-climb an airplane
---Flatten at top and form anvil shape
---With hail and heavy rain form cumulonimbus
---Make lightning and thunder lasting less than an hour
---Is where the cirrus clouds gather into ripples and groups to make beautiful sunsets
---High layer with more moisture than air below
---Feather-like curls of ice crystals
---Flat layers of cirrus clouds
---First a mass of cold polar air moves southward over the western Pacific ocean
---The cold mass runs into a warm air mass of similar size
---flow side by side in opposite directions until a part of the warm mass rises over heavy cool air
---The cool air breaks into other directions as it tries to fill the void caused by the rising warm air
---It cannot go straight because of the coriolis force of the spinning earth so it curves to the right
---This, in turn causes the entire air mass of hot and cold to turn left until it becomes a cyclone
---At the center of the cyclone the rising warm air cools and its moisture becomes rain=storm
---The storm spins and moves along the jet route until reaching the west-coast of North America
---This occurs over and over with each storm usually cold, warm, cold warm, cold warm
---Frontal temperatures are relative so that a cold front could be followed by even colder fronts
---At the Bay Area the storm has changed the faster cold front catches up with the warm front
---Now it goes below the warm front with the cold front ahead so the warm front is above the ground
---The warm front is occluded and drops rain through the cold fronts; nimbostratus is now cumulonimbus
---Thus California may be hit by a succession of storms with the worst moving in from the south
---The winds will vary from south west to south east and seldom used runways will be put to use.
---Winds from the east and northeast would cause stagnation of the ocean winds and smog.
---Winter winds vary as do summer winds and rain from valley to valley is often doubled or more
---Unlike to fogs from the ocean the rains can come from all directions with all temperatures
---Annual rainfall varies in less than 100 miles of coast from 52 to 14 inches
---Severe storms with winds and flooding occur about every ten years.
---A fog of many names as ground fog, tule fog, it is caused by the sun lifting ground moisture
---Radiation fog can last for days making all flight difficult because of restrictions to visibility
---Little fog may exist just before sunrise but will lift and burn off all day long.
---Where the coldest air gathers the ground moisture is turned into radiation fog
---Flight visibility will be much better up and down rather than on a slant angle
---A wind is all it takes to break up radiation fog.
---The radiation fog can accumulate and become hundreds of feet thick day and night
---Cold areas of inland Valley move the radiation fog to the Bay Area opposite to summer fogs
---The closer the ocean the warmer the winter weather, the more rain and less fog
Enter Global Forces
---The U.S. is home to masses of flowing air the largest and coldest coming from Canada
---This flow draws the warm from Mexico and ocean making California warm in December
---Occasionally the cold from Canada turns on California and forcefully or lightly with tornadoes
---The jet stream gives opportunities for extreme heat to hit California what will draw in ocean air
---With the valley cool again the winds slack off and the weather cycle begins again
I wrote this little proggy to get the local conditions at my airport quickly. I thought some you might be interested in checking it out. It's a little rough but I thought if you guys are game, it would be
nice to have some feedback. It's free. No commercial aspirations....
Direct User Access Terminal System (DUATS) A computer based program providing NWS and FAA weather products that are normally used in pilot weather briefings.
Low-level Windshear Alert System (LLWAS) A system installed at many large airports, that continually monitors surface winds at remote sites on the airport. A computer evaluates the wind differences from the remote sites, and automatically provides alerts if a low-level wind shear problem exists.
METAR Aviation Routine Weather Report. An observation of surface weather which is reported in a standard format. The international weather reporting code was adopted in the U.S. on June 1, 1996.
Microburst Small-scale intense downdrafts which, on reaching the surface, spread outward in all directions from the downdraft center. This causes the presence of both vertical (as strong as 6,000 feet per minute) and horizontal (distances of one nautical mile or less) wind shears, which can be extremely hazardous to all types and categories of aircraft, especially at low altitudes. Due to their small size, short life span, and the fact that they can occur over areas without surface precipitation, microbursts are not easily detectable using conventional weather radar or wind shear alert systems.
Night The time between the end of evening civil twilight and the beginning of morning civil twilight, as published in the American Air Almanac, converted to local time. The recent experience requirements of 14 CFR, section 61.57, require a pilot carrying passengers during the period beginning one hour after sunset and ending one hour before sunrise, to make at least three takeoffs and landings to a full stop during the period beginning one hour after sunset and ending one hour before sunrise within the preceding 90 days.
TAF Terminal Aerodrome Forecast. Provides weather conditions expected to occur within a five nautical mile radius of the runway complex at an airport.
Terminal Doppler Weather Radar (TDWR) Installed at many U.S. airports that are vulnerable to thunderstorms and microbursts. TDWR provides a narrower radar beam and greater power than so-called "network radars" (WSR-88D), and therefore, give a more detailed measure of wind shear in the vicinity of the airport.
Doppler Systems Doppler radars which measure a profile wind movement in the atmosphere. Profilers can measure wind speed and direction differences that can predict direction tornadoes will go. Dopplers, can determine humidity and temperature expectations well.
Wind Shear The rate of change in direction or speed of wind per unit distance; called wind
shear regardless of direction.
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Continued on 5.542 METAR Weather