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THUNDERSTORM — DGCA CPL Aviation Meteorology
Chapter J13 of the Aviation Meteorology paper. 35 practice questions in the Avielevate bank, every one with its answer key, filterable into a timed set on this chapter alone.
What this chapter covers
The learning objectives we file THUNDERSTORM questions under, and how many sit behind each. These come straight out of the bank and are regenerated whenever it changes — they are what is there today, not a claim.
| Learning objective | In the bank |
|---|
| __GEN__ General | 35 questions |
Sample THUNDERSTORM questions, answered and explained
Real questions from this chapter, with the answer marked and the reasoning written out — the same explanations you get inside the app.
0322033 · THUNDERSTORM
The trigger action for a thunderstorm may be provided by:
- AClear night sky, no wind
- BOrographic lifting
- CHigh pressure
Why that is the answer
**Concept**
A thunderstorm needs three ingredients: **moisture**, **instability** (a steep lapse rate, so rising air keeps rising) and a **trigger action**. The trigger is whatever gives the air its first upward push, lifting it until it is warmer than its surroundings and can carry on by itself.
**Explanation**
Common triggers are:
- **surface heating** (heat or convective thunderstorms)
- **orographic lifting**: wind blowing against hills or mountains is forced up the slope
- **frontal lifting**: a cold front pushing under warm air
- **convergence**: air flowing together near the ground has nowhere to go but up
Look at the diagram. Moist air meeting a mountain is forced to rise up the windward slope. It expands and cools, reaches its dew point and forms cloud. If the air is unstable, the lifted air stays warmer than its surroundings and keeps rising on its own, building cumulonimbus over the mountain.
**Applying it to the question**
A trigger can be provided by **Orographic lifting**. A clear night with no wind cools the ground and makes the lower air stable, which suppresses storms. High pressure brings sinking air, which warms and dries as it descends and also suppresses storms.
**Remember for DGCA:** triggers lift the air: heating, orographic lift, fronts and convergence. High pressure and calm clear nights work against thunderstorms.
Image credit: Depunity, CC BY-SA 4.0, via Wikimedia Commons.
0322035 · THUNDERSTORM
Over valleys and foothills, thunderstorms generally occur:
- AAfternoon
- BNight & early morning
Why that is the answer
**Concept**
Over flat land, heat-type thunderstorms usually form in the **afternoon**, when the Sun has heated the ground most. **Valleys and foothills** are different, because hills create their own local winds at night.
**Explanation**
After sunset the hill slopes cool quickly by radiation. The air touching them becomes cold and dense and **drains down the slopes** into the valley, like water running downhill. This downslope flow is called a **katabatic wind**.
The cold air slides underneath the warmer, moist air lying over the valley floor and in the foothill plains, and **lifts** it. If that air is moist and unstable, the lifting is enough to form cumulonimbus clouds. At the same time the cloud tops cool by radiation, which steepens the lapse rate further. The storms therefore develop late in the night and in the **early morning**. Look at the right panel of the diagram.
This is why places at the foot of the Himalaya, and valleys such as those of Assam, often get thunderstorms at night.
**Applying it to the question**
Over valleys and foothills, thunderstorms generally occur at **Night & early morning**. The afternoon is the typical time over open plains.
**Remember for DGCA:** plains = afternoon; sea = night; valleys and foothills = night and early morning.
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Frequently asked
How many THUNDERSTORM questions are there for the DGCA CPL Aviation Meteorology paper?
Avielevate's bank carries 35 published THUNDERSTORM questions for Aviation Meteorology, mapped across 1 learning objective. Every one has its answer key, and explanations are being written across the whole bank.
How much of the Aviation Meteorology paper is THUNDERSTORM?
The DGCA does not publish a per-chapter breakdown of its papers, so nobody can honestly tell you — and we will not guess. What we can tell you is what students who have just sat a paper reported meeting, which is measured rather than rumoured: that is the exam recall report inside the app.
What is the best way to revise THUNDERSTORM?
Sit a short timed set on this chapter alone, tag how sure you were of each answer, then drill the two that actually leak marks: the ones you got right while guessing, and the ones you got wrong while confident. Avielevate does that tagging for you and puts anything you got wrong back in front of you on a spaced schedule.
The rest of the Aviation Meteorology paper
One account covers every chapter of every paper.
← All Aviation Meteorology chapters · All six DGCA CPL papers