AWOS
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 !!
ASOS (newest)
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
Replacing AWOS.
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
ATIS
Tower, airport manager, FBO, local radio station
ASOS is telephone accessible
VOR/VORTAC
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
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