Met 11 - T h u n d e r s t o r m s

What are the main hazards of thunderstorms for pilots?

Strong winds, heavy rain, hail, lightning, turbulence, windshear, downdrafts, icing, tornadoes

What is the universal advice for thunderstorms?

Stay well away from them

What three conditions are required for a thunderstorm to form?

Instability, moisture, and a lifting trigger

What is the Saturated Adiabatic Lapse Rate (SALR)?

Approximately 1.5°C per 1000 ft

What is the Environmental Lapse Rate (ELR)?

Approximately 2°C per 1000 ft

When does condensation occur in rising air?

When the dew point is reached

How does warm moist air behave in an unstable atmosphere?

It rises and accelerates due to buoyancy

What cloud type indicates medium-level instability?

Altocumulus Castellanus

Why does warm air hold more moisture?

Because warmer air can hold more water vapor than cooler air

What kind of front can most commonly trigger thunderstorms?

Cold fronts

What is a squall line?

A line of thunderstorms forming ahead of a cold front

Where do most UK fronts occur without thunderstorms?

In maritime polar air masses

What local trigger can cause summer thunderstorms?

Surface convection over hot spots like cities

What is orographic lifting?

Air rising due to terrain like hills or mountains

What is a convergence zone?

Area where different airflows meet, triggering thunderstorms

What are the three stages of a thunderstorm?

Developing, mature, and dissipating

What marks the developing stage of a thunderstorm?

Towering cumulus (TCU) with strong updrafts

What is a sign of a strong developing cumulus?

Hard edges and bright white appearance

What happens in the mature stage of a thunderstorm?

Precipitation begins, lightning, and strong vertical currents

What is a gust front?

A cool downdraft spreading ahead of a thunderstorm

What marks the dissipating stage of a thunderstorm?

Anvil-shaped cloud top and weakening of the storm

How long does a single-cell thunderstorm last?

Less than an hour, but clouds may persist 2–3 hours

What is a supercell?

A severe storm where precipitation is separated from updrafts

Why do supercells last longer than regular thunderstorms?

Because they tilt and self-propagate

What is a common cloud type in thunderstorms?

Cumulonimbus (CB)

What visibility hazard is caused by snow in a thunderstorm?

Can reduce visibility to 50 meters

Where can hail come from in a thunderstorm?

From the anvil overhang, outside the main cloud

What color may indicate a hail-producing thunderstorm?

A greenish tint

What is mammatus cloud?

Cloud marking downdrafts and severe turbulence

Where is icing most severe in a thunderstorm?

Between 0°C and -20°C above freezing level

What is windshear?

A sudden change in wind speed and/or direction

What is a microburst?

A localised intense downdraft that is dangerous during takeoff or landing

What is virga?

Rain falling from a cloud but evaporating before reaching the ground, indicating downdrafts

What does a gust front indicate?

Potential for windshear and turbulence, often marked by roll cloud

How strong can outflow winds be in a thunderstorm?

Up to 40 knots

How strong can gusts from microbursts be?

Up to 60 knots or more

What is a tornado?

A rotating column of air with winds up to 200 knots

How can a tornado appear?

As a funnel cloud or waterspout

What happens to aircraft struck by lightning?

Metal aircraft often survive, but avionics and compasses may be affected

What effect does lightning have on radios?

Increased static and interference, especially at low frequencies

What direction does an ADF needle point during a thunderstorm?

Toward the nearest active thunderstorm cell

How do you estimate distance from a thunderstorm?

Count seconds between flash and thunder; 5 seconds = 1 mile

What forecast code indicates a 30% chance of thunderstorms?

PROB30 in a TAF

What is a TAF?

A Terminal Aerodrome Forecast

What is a METAR?

A routine aviation weather report showing current conditions

What cloud codes indicate thunderstorms in a METAR?

BKN or OVC with CB (cumulonimbus)

What dew point increases thunderstorm severity?

A dew point around +20°C or more

Which air mass increases thunderstorm risk in the UK?

Returning polar maritime air

What air mass brings the most severe thunderstorms?

Tropical continental air

Why are embedded thunderstorms dangerous?

They are hidden in other clouds or haze and hard to detect visually

What should a pilot do if haze suddenly darkens?

Take immediate evasive action

What type of thunderstorms are easier to avoid?

Convective thunderstorms

Which thunderstorms are hardest to avoid?

Frontal, trough, or line-squall thunderstorms

What is the minimum distance to stay away from a CB cloud?

At least 10 miles, ideally 20 miles

Can turbulence exist far from a thunderstorm?

Yes, up to 20 miles downwind

Should you take off with a thunderstorm nearby?

No, avoid takeoff under or near a thunderstorm

What should you do if your destination is affected by a thunderstorm?

Hold clear or divert

What is the safest place for an aircraft during a thunderstorm?

In a hangar

Should large cumulus clouds be treated with caution?

Yes, they may have thunderstorm characteristics