AIP GEN 3.5 Section 3 gives general information regarding aviation weather reports and forecasts.

AIP GEN 3.5 Section 18 gives specific information regarding area forecasts for use below FL200.

Some important points to note include :

• TEMPO and INTER on an area forecast indicate significant variations in weather conditions from the previously given mean conditions. The conditions are of a temporary or intermittent nature, expected during the period identified in the forecast. The period of time during which the variation is expected is given in the format ddhh/ddhh eg. 0108/0114 means from 0800 UTC until 1400 UTC on the 1st.
  • TEMPO is used to indicate a change in the prevailing weather conditions that is expected to last for periods of between 30 and 60 minutes in each instance;
  • INTER is used to indicate changes expected to occur frequently for periods of leass than 30 minutes duration, the conditions fluctuating almost constantly, between times specified in the forecast.
• The amount of Cumulonimbus (CB) cloud is indicated on non-aerodrome forecasts as:
  • ISOL = isolated – for individual CBs;
  • OCNL = occasional – for well sepereated CBs;
  • FRQ = frequent – for CBs with little or no spacing.
• GOOD refers to visibility of 10 km or greater over the entire forecast area;
• FM = from and BECMG = becoming: are used when significant changes (both improvements and deteriorations) are expected to occur;
• Cloud Height Datum: in aerodrome and trend forecast, cloud heights are expressed above the aerodrome elevation. In other forecasts heights are expressed as a flight level or with reference to mean sea level;
• PROB% is used to indicate an expected 30 or 40% probability of occurence of a weather phenomena eg. PROB30 Fog 1822 – there is a 30% probability of fog occuring between 1800 and 2200 UTC.

We have an aviation weather decode card available for download which can be used as a quick reference guide for interpreting aviation weather reports including ARFOR, TAF, METAR, SPECI and SIGMET.

Here is an additional resource including example severe weather area forecasts.

Back to Pilot Exam Help Index

Decoding Aviation Weather Reports - ARFOR - Technical data content credited to Mr Steve Griffin