CFI Instrument Practical Test Standards, FAA-S-8081-9B, June 2001

III. Preflight Preparation

A. Weather Information

2. Weather reports and forecasts
    a. METAR, TAF, FA and radar reports
      1) Aviation routine weather report (METAR)
        a) ICAO world standard aviation weather report with country-specific modifications
        b) METAR elements
          i) Type of report (METAR or SPECI)
          ii) ICAO 4-letter station identifier
          iii) Date and time
          iv) Modifier
          v) Wind direction (TRUE) and velocity
          vi) Prevailing visibility (SM)
          vii) Runway visual range (when reported) (FT)
          viii) Weather phenomena
          ix) Sky condition
          x) Temperature/dew point (°C)
          xi) Altimeter setting
          xii) Remarks
          xiii) Sensor status
      2) Aerodrome (terminal area) forecast (TAF)
        a) Concise statement of expected weather conditions within 5 SM of selected airports during a specifiec time period (usually 24 hours)
        b) Uses same codes as METARs
        c) Scheduled four times daily beginning at 0000, 0600, 1200 and 1800Z
        d) Format
          i) Type of report (TAF or TAF AMD)
          ii) ICAO 4-letter station identifier
          iii) Date and time forecast prepared
          iv) Valid period date and time
          v) Forecast weather
          • Wind (TRUE)
          • Visibility (SM)
          • Weather phenomena
          • Sky condition
          • Wind shear at or below 2,000 feet (optional)
        e) Probability of precipitation events indicated by PROB (PROB 30 = 30-39%)
        f) Forecast change indicators
          i) FM ("from") indicates rapid change in prevailing conditions usually over less that 1 hour
          ii) BECMG ("becoming") indicates more gradual change usually usually over up to 2 hours
          iii) TEMPO ("temporary") indicates conditions expected to occasionally occur and last less than 1 hour at a time over less than half the time period
        g) TAFs helpful in deciding if an alternate airport is required and approved under 14 CFR Part 91.169
      3) Aviation area forecast (FA)
        a) Forecast of visual meterological conditions (VMC), clouds and general weather over an area the size of several states
        b) Issued three times per day by the AWC in Kansas City, MO, for each of the six areas in the contiguous 48 states
        c) FA elements
          i) Communication and product header
          • Area covered
          • Valid time
          ii) Precautionary statements
          iii) Synopsis (18-hour period)
          iv) VFR clouds and section
          • 12-hour specific forecast +
          • 6-hour categorical outlook
          • OCNL = greater than 50% probability for less than half of period
          • WDLY SCT = less than 25% of area
          • SCT or AREAS = 25-50% of area
          • NMRS or WDSPRD = 55% or more of area
          • OTLK
            • WND = winds 20 kts or greater
            • IFR = ceiling < 1000 ft and/or visibility < 3 SM
            • MVFR = ceiling 1000-3000 ft and/or visibility 3-5 SM
            • VFR = ceiling > 3000 ft and visibility > 5 SM
        d) Hazardous weather conditions such as IMC, icing and turbulence are not in the FA, but in in-flight weather advisories (AIRMETs, SIGMETs and convective SIGMETs)
      4) Radar weather reports (SD)
        a) Indicate general areas of precipitation (rain, snow, thunderstorms) observed by radar
        b) Radar stations report each 35 minutes past the hour
        c) Report type, intensity and echo top of precipitation
        d) Automatically generated from WSR-88D weather radar data
        e) SD elements
          i) Radar station location and time (UTC)
          ii) Echo pattern
          • LN = line (at least 30 NM long with length at least 4 times width and covering at least 25% of area)
          • AREA
          • CELL
          iii) Coverage in tenths
          iv) Type and intensity of weather
          • Type
            • R rain
            • RW rain showers
            • S snow
            • SW snow showers
            • T thunderstorm
          • Intensity
            • - light
            • (none) moderate
            • + heavy
            • ++ very heavy
            • X intense
            • XX extreme
          v) Aximuth (TRUE) and range (NM) from radar station
          vi) Dimensions of echo pattern
          vii) Cell movement
          viii) Maximum top and location (MTS: satellite data also used to measure top)
          ix) AUTO: automated from WSR-88D weather radar data
          x) Digital section: used to prepare radar summary chart
          xi) Blank report
          • PPINE = radar normal, no echoes detected
          • PPINA = not available
          • PPION = inpoerative, out of service
        f) Include SDs in preflight planning
          i) Note location, intensity and direction of movement of precipitation
          ii) Airborne, update by contacting Flight Watch, viewing data-linked NEXRAD images, use of airborne radar and visual sighting

Greg Gordon MD, CFII