Sep 2012 Lesson 4.7 Meteorology Precipitation, Fog & Thunderstorms

Reference From the Ground Up Chapter 6.8 & 6.9: Precipitation, Fog & Thunderstorms Pages

Introduction Precipitation, fog and thunderstorms are weather effects that result from cloudy conditions and high humidity.Precipitation, fog and thunderstorms are weather effects that result from cloudy conditions and high humidity. Precipitation and fog can create visibility problems for aircraft. Thunderstorms can create lots of extreme weather that are dangerous to aircraft.Precipitation and fog can create visibility problems for aircraft. Thunderstorms can create lots of extreme weather that are dangerous to aircraft.

Outline PrecipitationPrecipitation FogFog ThunderstormsThunderstorms

Precipitation When water droplets (visible as a cloud) grow sufficiently in size and weight to fall due to gravity.When water droplets (visible as a cloud) grow sufficiently in size and weight to fall due to gravity. PrecipitationClouds Drizzle, freezing drizzle, snow grains Stratus, stratocumulus Snow/rain (continuous) Thick altostratus, nimbostratus Snow/rain (intermittent) Thick altostratus, stratocumulus Snow/rain showers Altocumulus, heavy cumulus, cumulonimbus Snow pellets, hail, ice pellet showers Cumulonimbus Ice pellets (continuous) Any rain cloud below freezing temperature Ice Prisms No clouds

Fog

Fog Fog is stratus cloud in contact with the groundFog is stratus cloud in contact with the ground Radiation FogRadiation Fog –Air cooled by cooling ground –Formed on clear nights, with moist air and light winds (2 – 5 kts) Advection FogAdvection Fog –Forms when warm, moist air moves over cool surface Upslope FogUpslope Fog –Caused by air moving up slope and expanding

Fog Steam FogSteam Fog –Cold air moves over warm water surface and picks up water vapour Precipitation-Induced Fog (AKA Frontal Fog)Precipitation-Induced Fog (AKA Frontal Fog) –Rain falling from warm air mass saturates cool air mass below Ice FogIce Fog –Forms when water vapour added to air saturated with ice crystals –Usually formed from engine exhaust

Thunderstorms

Thunderstorms A weather phenomena whose presence creates extremely serious hazards to flyingA weather phenomena whose presence creates extremely serious hazards to flying HazardsHazards –Turbulence, lightning, hail, icing, pressure, wind, rain Requirements for DevelopmentRequirements for Development –Unstable air –Lifting agent –High moisture content AvoidanceAvoidance –Stay at least 15 miles away and pass to the right –Do not fly under

Thunderstorms Types Air Mass ThunderstormsAir Mass Thunderstorms –Usually form on hot summer days in warm, moist air from convection –VFR weather around them, east to see and avoid Frontal ThunderstormsFrontal Thunderstorms –Normally in cold fronts –Can extend for hundreds of miles, and known as a Line Squall –Can be embedded in warm fronts

Thunderstorm Stages Initial or Cumulus StageInitial or Cumulus Stage –Strong updrafts –No precipitation Mature StageMature Stage –Updrafts and downdrafts –Precipitation starts Dissipating StageDissipating Stage –Downdrafts only –Precipitation ends

Next Lesson 4.8 – Meteorology Icing & Turbulence From the Ground Up Chapter 6.10 & 6.11: Icing & Turbulence Pages