Flight Categories

Category/
SPECI Criteria

Ceiling (feet)

  

Visibility (km, m)

VFR
(Visual Flight Rules)

> 3000 ft or None

and

> 8 km
8000 m

MVFR
(Marginal Visual Rules)

1000-3000 ft

and/or

5 to 8 km
5000-8000 m

IFR
(Instrument Flight Rules)

500-1000 ft

and/or

1.6 to 5 km
1600-5000 m

LIFR
(Low Instrument Flight Rules)

300-500 ft

and/or

0.8 to 1.6 km
800-1600 m

VLIFR
(Very Low Instrument Flight Rules)

< 300 ft

and/or

< 0.8 km
800 m

BECMG and TEMPO

Guidelines for using "BECMG" and "TEMPO" groups:

  • Indicate significant changes in the weather elements using the "BECMG" or "TEMPO" groups showing the time duration expected. The beginning and end times are included in whole hours UTC (encoded Z).
  • TEMPO indicator and its time group are used for expected fluctuations in meteorological conditions that may cross threshold values and last for less than an hour over less than half the forecast period. Longer fluctuations are represented by the "BECMG" group.
  • "FM" abbreviation is used when a set of forecast conditions are expected to change significantly. It is followed by a four-figure time group in whole hours and minutes indicating when change is expected to occur.
  • "PROB" abbreviation is used to indicate the possibility of alternative values for a forecast element. Include the probability in tens of percent and the time period during which the alternatives are expected after the forecast element followed by the alternative value. PROB can be used with TEMPO to indicate the probability of temporary fluctuations in conditions. Probabilities less than 30 percent should not be indicated using TEMPO, and probabilities greater than 50 percent should be represented instead using BECMG or TEMPO groups, or contained in a separate FM group.

Recommendation: The number of change and probability groups should be kept to a minimum and should not normally exceed five groups.

Conditional Groups


Wind
  • Wind direction shift by 60° or more when speed is 20 km/h (10 kt) or more
  • Mean surface wind speed is forecast to change by 20 km/h (10 kt) or more
  • Wind gusts of 20 km (10 kt) or more above mean wind speed of 30 km/h (15kt)
  • Be aware of your own criteria and change groups or amend the TAF if wind changes cross those operational thresholds. For example, a wind direction shift that would require a runway change. Include tailwind and crosswind thresholds.
Visibility
  • Changes (conditions improving or deteriorating) across the following values: 150, 350, 600, 800, 1500 or 3000 m; or 5000 m at airports using primarily visual flight rules

Weather
  • At the beginning or end, or intensity change of these weather phenomena:
    • Freezing precipitation
    • Moderate or heavy precipitation
    • Dust storm
    • Sandstorm
    • Or other phenomena expected to significantly impact visibility
  • At the beginning or end of these weather phenomena:
    • Ice crystals
    • Freezing fog
    • Low drifting dust, sand or snow
    • Blowing dust, sand or snow
    • Thunderstorm (with or without precipitation)
    • Squall
    • Funnel cloud (tornado or waterspout)

Ceiling
  • When the ceiling of BKN or OVC skies will change (lift or fall) and cross the following values: 30, 60, 150 or 300 m (100, 200, 500 or 1000 ft); or 450 m (1500 ft) at airports using primarily visual flight rules
  • When the amount of coverage of cloud below 450 m (1500 ft) is forecast to change: from SKC, FEW or SCT to BKN or OVC; or from BKN or OVC to SKC, FEW or SCT;

Vertical Visibility
  • When the vertical visibility will change (improve or deteriorate) and cross the following values: 30, 60, 150 or 300 m (100, 200, 500 or 1000 ft);
  • Any other criteria based on local aerodrome operating minima

Note: Other criteria based on local aerodrome operating minima are to be considered in parallel with similar criteria for the issuance of SPECI developed in response to Appendix 3, 2.3.2 l.

Cloud Codes

  • 60 = 10 km
  • 65 = 15 km
  • 70 = 20 km
  • 75 = 25 km
  • 80 = 30 km