Meteorological Forecast

Aerodrome Forecast

Aerodrome Weather Forecast

• Aerodrome forecasts are classified into four types:
  • Nowcasting: Valid for less than 24 hours.
  • Short-Range Forecast: Valid for 1–3 days.
  • Medium-Range Forecast: Valid for 4–10 days.
  • Long-Range Forecast: Valid for more than 10 days.
• Terminal Aerodrome Forecast (TAF):
  • 9-hour validity TAF is issued every 3 hours for domestic flights.
  • 12–30 hour validity TAF is issued every 6 hours for international flights.
  • 9-hour TAF is broadcast on VOLMET.
• Landing (Trend) Forecast: Appended to METAR or SPECI and valid for 2 hours. NOSIG indicates no significant change is expected. Probability groups are not used in trend forecasts.
• Take-off Forecast: Issued approximately 3 hours before ETD and contains:
  • Surface wind averaged over 2 minutes.
  • Temperature.
  • QNH.

TAF – Time, Wind and Visibility

• Report Type and Location: TAF followed by the ICAO aerodrome indicator (e.g., TAF VIDP).
• Date and Time: UTC issue time and validity period (e.g., 270630Z 2707/2716).
• Wind Direction: True direction expressed in three digits at 10° intervals.
• Variable wind extremes may be reported (e.g., 26005KT 220V360).
• Wind Speed: Mean wind speed and gusts (when gusts exceed the mean by 10 kt or more) are reported in knots or metres per second.
• P99 indicates gusts greater than 99 knots.
• Visibility: Prevailing visibility reported in metres.

TAF – Weather and Clouds

• The weather group contains a Qualifier, Descriptor, and Weather Phenomenon, similar to METAR (e.g., -SHRA).
• Clouds are reported as height above aerodrome level (QFE) in ascending order of cloud amount.
• High clouds are included only when covering a significant area. Only CB (Cumulonimbus) is specifically identified.
• NSC (No Significant Clouds) means:
  • No cloud below 5000 ft or the Minimum Sector Altitude (MSA), whichever is higher.
  • No Cumulonimbus (CB) clouds.
• TAF does not include forecasts of:
  • Temperature.
  • Dew Point.
  • QNH.
  • Recent Weather.
  • Wind Shear.
  • Runway State.

Temporary and Permanent Changes

• Permanent Change:
  • FM (From): Indicates a permanent change from the specified date and time.
    Example: FM271220 27010KT 4000 TSRA BKN010CB
  • BECMG (Becoming): Indicates gradual change during the specified validity period.
    Example: BECMG 1309/1311 4000 TSRA BKN010CB
• Temporary Change:
  • TEMPO indicates temporary fluctuations that may occur at any time within the specified period.
  • Each fluctuation lasts for less than one hour and occupies less than half of the forecast period.
  • Example: TEMPO 1312/1314 TSRA BKN010CB

Probability and Amended Forecast

• Probability Groups:
  • Probability is expressed as a percentage.
  • Example: PROB40 indicates a 40% probability.
  • Probability groups may accompany either permanent or temporary changes.
• Amended Forecast: Forecast amendments are indicated using TAF AMD.

Aerodrome Warnings

• Aerodrome warnings are issued for weather conditions likely to adversely affect aircraft on the ground.
• Warnings are generally valid for less than 4 hours.
• Wind Criteria:
  • Wind speed greater than 30 kt.
  • Wind speed greater than 20 kt with a direction change of at least 45°.
• Weather Warnings: Squall, Tropical Cyclone (TC), Duststorm (DS), Sandstorm (SS), Thunderstorm (TS), Hail (GR), Frost, Snow (SN), Hoar Frost, Rime Ice, Freezing Rain, Sand or Dust Storm, Volcanic Ash (VA), and Tsunami.
• Warnings for gliders, helicopters and light aircraft are issued when surface wind is expected to reach 17 kt or more.
• Wind shear warnings cover the area up to 500 m (1600 ft) above the runway affecting aircraft during approach, take-off, circling approach or while on the runway.
• Wind shear information is also included in METAR, SPECI, and SPECIAL.

Types of Area Forecast

• ARFOR (Area Forecast): Coded or tabular forecast providing:
  • Upper winds.
  • Upper-air temperatures.
  • Significant weather.
  • Clouds.
  • Freezing level.
  • Turbulence.
  • Icing.
  • Jet stream.
  • Tropopause.
  • Maximum wind.
  • Wind shear.
  • Airfield warnings.
• CODAR: Upper-air report from aircraft other than dedicated weather reconnaissance aircraft.
• WINTEM: Forecast of upper-level wind and temperature.
• ROFOR (Route Forecast): Coded route forecast including upper winds, upper-air temperature, significant weather, clouds, freezing level, turbulence, icing, jet stream, tropopause and maximum winds.
• Local Area Forecast:
  • Covers a radius of 100 NM.
  • Valid for 8 hours.
  • Issued three times daily:
    • 2130 UTC (Valid 2200–0600 UTC)
    • 0530 UTC (Valid 0600–1400 UTC)
    • 1330 UTC (Valid 1400–2200 UTC)
  • Includes surface wind, visibility, weather, clouds, upper winds, temperature, sunrise, sunset and warnings.

Example of Area and Route Forecast

• Area and Route Forecasts are designated as ARFOR and ROFOR.
• ARFOR provides a complete forecast for a geographical area.
• ROFOR provides a forecast for a specified route.
• The overall format of ARFOR and ROFOR is similar.

Comparison Between ARFOR and ROFOR

Area Forecast (ARFOR)

• Issuing station.
• Date and time of issue.
• Applicable flight levels.
• Validity period (From / To).
• Wind speed units.
• Area description (coordinates or plain language).
• Visibility.
• Weather in code.
• Cloud layers (lowest to highest including CB).
• Cloud layer altitudes and freezing level.
• Icing type, altitude and thickness.
• Turbulence information.

Route Forecast (ROFOR)

• Issuing station.
• Date and time of issue.
• Applicable flight levels.
• Validity period (From / To).
• Wind speed units.
• Route description divided into sectors.
• Upper wind and temperature.
• Tropopause pressure level and temperature.
• Jet stream location, altitude and wind speed.
• Maximum wind altitude, speed, direction and wind shear.
• Supplementary information such as lowest pressure, BECMG and TEMPO.