A Pilot's Guide to Aviation Weather Services
This brochure is designed to help you use the NATIONAL AVIATION WEATHER SYSTEM to the fullest extent possible. The information and services described here are available from the National Weather Service (NWS), the Federal Aviation Administration (FAA), and information service companies.
For More Information
For more detailed weather information consult AVIATION WEATHER (FAA Advisory circular 00-6A); AVIATION WEATHER SERVICES (FAA Advisory Circular 00-45); and the AIRMAN'S INFORMATION MANUAL, (Chapter 7, Safety of Flight). These publications are available at local government bookstores and from the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.
The following is a list of abbreviations and acronyms used in this brochure:
Preparation for your weather briefing:
A.M. WEATHER is a 15-minute television weather program designed for pilots and can be seen on more than 300 PBS stations Monday through Friday mornings. Check your local TV listings for exact time and station.
Meteorological and aeronautical information is provided by continuous recorded Transcribed Weather Broadcasts (TWEB), the Pilot's Automatic Telephone Answering Service (PATWAS), and the Telephone Information Briefing Service (TIBS). Complete weather information is available by telephone call or visit to the nearest FAA Flight Service Station (FSS) or designated NOAA Weather Service Office. Information is also available from private commercial vendors. During periods of marginal weather, briefers are busy and telephone delays may occur. While waiting for the briefer, you may get basic information from TWEBs, PATWAS, or TIBS - - but do continue to wait for the briefer. The latest hourly aviation weather observations from distant stations are normally available by 5 minutes past the hour.
Pilots may obtain Federal pre-flight weather briefings tailored to your individual needs. Any one of three types of briefings may be requested: standard, abbreviated or outlook.
A standard briefing should normally be requested even when you have received prerecorded or mass media weather information (e.g., TWEB, A.M. WEATHER, etc.). After giving the briefer the necessary background information, you will automatically receive the following:
* Not provided by NWS briefers
An abbreviated briefing should be requested if you have used prerecorded or mass media weather information to make a go/no-go decision and only selected additional information is required. You should provide the pertinent background information, tell the briefer what previous information source you have used, and ask for an abbreviated briefing with specified observation or forecast products.
An outlook briefing should be requested for long-range flight planning. This briefing contains forecasts for a flight beginning more than 6 hours in the future. An abbreviated or standard briefing should then be obtained when closer to the time of departure.
For your pre-flight weather briefing, give the briefer the following background information:
Type of flight VFR, IFR or DVFR
After receiving weather information, either for short or long-range flights, consider carefully if conditions are suitable for your intended flight.
During marginal VFR or IFR conditions, keep a particularly close check on en route, terminal and alternate airport weather. Routine weather information is available by radio from any FAA FSS. Selected FSSs broadcast In-flight Advisories (SIGMETs, Convective SIGMETs, Center Weather Advisories [CWAs], Alert Weather Watches [AWW] and AIRMETs) and severe weather information. TWEBs also can be received while airborne. Pilots should monitor Hazardous In-flight Weather Advisory Service (HIWAS) weather broadcasts routinely. See the Airport/Facility Directory (A/FD) and aeronautical charts for frequencies. Do not hesitate to request specific information from the En Route Flight Advisory Service (EFAS) - "Flight Watch" - on 122.0 MHZ below 18,000 feet MSL. See the A/FD for high altitude frequencies. In-flight briefing procedures are explained in detail in the Airman's Information Manual.
Prior to descent, request current weather for the terminal area and conditions at your destination airport. At many airports, this information is continuously broadcast on ATIS, ASOS, AWOS, or selected navigation aids. These broadcasts reduce pilot and controller communications workloads.
Aviation Weather Support Products
CEILING AND VISIBILITY CATEGORIES
EXAMPLE OF TERMINAL FORECAST:
DCA 221010 10 SCT C18 BKN 5SW- 3415G25 OCNL C8 X ½ SW.
12Z C50 BKN 3312G22.
04Z MVFR CIG..
Decoded Example: Washington National Airport for the 22nd of the month valid from 10Z to 10Z. Scattered clouds at 1000 feet, ceiling 1800 feet broken, visibility 5 miles in light snow showers, surface wind 340 degrees at 15 knots, gusts to 25 knots. Occasional ceiling 800 feet, sky obscured, visibility one-half mile in moderate snow showers. By 12Z becoming ceiling 5000 feet broken, surface wind 330 degrees at 12 knots, gusts to 22 knots. The categorical outlook for the last 6 hours beginning at 04Z calls for marginal VFR conditions due to ceiling.
AREA FORECASTS (FA) provide an 18-hour synopsis of expected weather patterns; a 12-hour forecast of VFR cloud cover, weather and visibility; and a 6-hour categorical outlook. FAs are prepared 3 times a day (4 times a day in Alaska and Hawaii) and are supplemented and updated by SIGMETs, AIRMETs, and by FA amendments. Heights in the FA are above mean sea level (MSL) unless stated as above ground level (AGL). Ceilings (CIG) are always AGL.
WIND and TEMPERATURE ALOFT FORECASTS (FD) are 6, 12, and 24-hour forecasts of wind direction, speed, and temperatures for selected altitudes to 53,000 feet MSL at specified locations. Direction is relative to true north rounded to the nearest 10 degrees. Speed is in knots. Temperatures aloft (in degrees Celsius) are included with wind data for all but the 3000-foot MSL level and those levels within 2500 feet of the ground. Temperatures above 24,000 feet MSL are always negative. Winds at other locations and altitudes can be obtained by interpolation.
EXAMPLE OF WINDS ALOFT FORECAST:
Decoded example: For Atlantic City, N.J., at 6000 feet MSL wind from 280 degrees true at 33 knots, temperature 2 degrees Celsius.
IN-FLIGHT ADVISORIES warn pilots of potentially hazardous weather. They include SIGMETs, CONVECTIVE SIGMETs, AIRMETs, and Center Weather Advisories (CWA). SIGMETs warn of hazardous conditions of importance to all aircraft i.e. severe icing or turbulence, duststorms, sandstorms, and volcanic ash. AIRMETs warn of less severe conditions which may be hazardous to some aircraft or pilots. SIGMETs are issued as needed. AIRMET bulletins are issued routinely and supplement the Area Forecast (FA). CONVECTIVE SIGMETs are issued hourly for thunderstorms in the continuous U.S. Center Weather Advisories, issued as needed, are detailed advisories of conditions which meet or approach SIGMET or AIRMET criteria.
EXAMPLE OF SIGMET:
Decoded Example: SIGMET OSCAR 2 is valid until 2100Z on the 5th day of the month. For Kansas and Nebraska from Pawnee City VORTAC to Oswego VORTAC to Liberal VORTAC to Pawnee City VORTAC. Severe turbulence below 6000 feet expected due to strong northwesterly flow behind a cold front. Conditions continuing beyond 2100Z.
TRANSCRIBED WEATHER BROADCASTs (TWEB) are continuous broadcasts of recorded NOTAM and weather information prepared for a 50-nautical mile wide zone along a route and for selected terminal areas. TWEBs are broadcast over selected NDB and VOR facilities and generally contain a weather synopsis, in-flight advisories, route and/or local vicinity forecasts. Winds Aloft Forecasts, current weather reports, NOTAMs, and special notices. TWEB outlets are listed below by state:
VOR facilities (108.00 - 117.95 MHZ) have line-of-sight range.
NDB (L/MF) facilities (190 - 535 kHz) have varying ranges.
PILOT'S AUTOMATIC TELEPHONE WEATHER ANSWERING SERVICE (PATWAS), and the TELEPHONE INFORMATION BRIEFING SERVICE (TIBS), provide continuous recordings of weather and aeronautical information. The information may include area and/or route briefings, airspace procedures, and special announcements. Telephone numbers for PATWAS and TIBS locations are found in the Airport/Facility Directory.
TWEBs, PATWAS, and TIBS are for preflight or inflight planning and should not be considered a substitute for formal preflight briefings.
|REPORTS INCLUDE:||Aircraft Identification|
|Coordinated Universal Time (UTC) or Z|
|Intensity and Type of Icing or Turbulence|
|Indicated Air Speed|
|Duration of Icing or Turbulence|
|REPORTING DURATION:||Occasional - Less than 1/3 of the time.|
|Intermittent - 1/3 to 2/3.|
|Continuous - More than 2/3.|
|Trace||Ice becomes perceptible. Rate of accumulation slightly greater than rate of sublimation. It is not hazardous even though deicing/anti-icing equipment is not utilized, unless encountered for an extended period of time (over 1 hour).|
|Light||The rate of accumulation may create a problem if flight is prolonged in this environment (over 1 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||The rate of accumulation is such that even sort encounters become potentially hazardous and use of deicing/anti-icing or diversion is necessary.|
|Severe||The rate of accumulation is such that deicing/anti-icing equipment fails to reduce or control the hazard. Immediate diversion is necessary.|
From 50 miles south of Albuquerque to 30 miles north of Phoenix, 1210Z to 1250Z, occasional Moderate Rime Ice, 10,000 feet, PA34.
REACTION IN AIRCRAFT
|Light||Turbulence that momentarily causes slight erratic changes in altitude and/or attitude (pitch, roll, yaw). Report as Light Turbulence.* OR Turbulence that causes slight, rapid and somewhat rhythmic bumpiness without appreciable changes in altitude or attitude. Report as Light Chop.||Occupants may feel a slight strain against seat belts or shoulder straps. Unsecured objects may be displaced slightly. Food service many be conducted and little or no difficulty is encountered when walking.|
|Moderate||Turbulence that is similar to Light Turbulence but of greater intensity. Changes in altitude and/or attitude occur but the aircraft remains in positive control at all times. It usually causes variations in indicated airspeed. Report as Moderate Turbulence.* OR Turbulence that is similar to Light Chop but of greater intensity. It causes rapid bumps or jolts without appreciable changes in aircraft altitude or attitude. Report as Moderate Chop.||Occupants feel definite strains against seat belts or shoulder straps. Unsecured objects are dislodged. Food service and walking are difficult.|
|Severe||Turbulence that causes large, abrupt changes in altitude and/or attitude. It usually causes large variations in indicated airspeed. Aircraft may be momentarily out of control. Report as Severe Turbulence.*||Occupants are forced violently against seat belts or shoulder straps. Unsecured objects are tossed about. Food service and walking are impossible.|
|Extreme||Turbulence in which the aircraft is violently tossed about and is practically impossible to control. It may cause structural damage. Report as Extreme Turbulence.*|
|*High level turbulence (normally above 15,000 feet MSL) not associated with cumuliform cloudiness, including thunderstorms, should be reported as CAT (Clear Air Turbulence) preceded by the appropriate intensity, or light or moderate chop.|
NOTE: Pilots should report location(s), time (UTC or Z), intensity, whether in or near clouds, altitude, type of aircraft and when applicable, duration of turbulence. Duration may be based on time between two locations or over a single location. All locations should be readily identifiable.
Over Omaha, 1232Z, Moderate Turbulence, in cloud, Flight Level 310, B767.