Rain
Rain (RA) is liquid precipitation with drops of 0.5 mm or greater in diameter, falling from clouds. It is one of the most common forms of precipitation encountered in Canadian aviation. Reported in METARs with intensity qualifiers: −RA (light rain), RA (moderate), +RA (heavy rain).
Aviation Effects of Rain
- Visibility: Moderate to heavy rain reduces forward visibility — relevant for VFR minimums and approach decision-making
- Runway contamination: Standing water and hydroplaning risk; landing distance can double on a wet runway
- Engine ingestion: Very heavy rain can cause piston engine rough running due to excessively rich mixture; turbine engines designed for rain ingestion
- Icing indicator: Rain at or near 0°C indicates freezing rain risk if temperature drops
Rain and Icing
When rain falls through a layer of air below 0°C it can become freezing rain. Rain at +2 to +4°C falling through ice-crystal cloud aloft is a warning sign — a temperature drop of a few degrees will produce freezing rain. Monitor TAFs and GFAs carefully when temperature and dew point are close and temperature is near 0°C.
Related Terms
See also: Freezing Rain, Precipitation, Visibility.