Precipitation Rate – Canadian Flight Trainers

Precipitation rate is the amount of precipitation falling per unit time, typically expressed in millimetres per hour (mm/hr). In aviation, precipitation rate determines the intensity of its effects: visibility reduction, runway contamination, and — for freezing precipitation — the rate of ice accretion on the airframe.

Precipitation Rate and Aviation Hazard

Light precipitation: Minor visibility reduction; relatively manageable icing in freezing conditions
Moderate precipitation: Significant visibility impact; moderate icing rate in freezing conditions; runway contamination
Heavy precipitation: Severe visibility reduction; rapid ice accretion; potential aquaplaning on wet runways

Convective vs. Stratiform

Stratiform precipitation (from nimbostratus cloud) is generally widespread and moderate intensity. Convective precipitation (from cumulonimbus) is intense and localized. A thunderstorm can produce rainfall rates exceeding 150 mm/hr in the core — creating near-zero visibility and potentially catastrophic icing if the temperature is near 0°C.

Related Terms

See also: Precipitation, Icing, Thunderstorm.