A pilot notices that a developing cumulonimbus cloud has a well-defined anvil top that is spreading out horizontally at high altitude. What does this feature indicate about the thunderstorm and the associated hazard?
- AThe storm has reached the tropopause, where stable air causes the cloud top to spread horizontally; hazardous turbulence and hail can still be thrown far downwind under the anvil
- BThe storm is in the cumulus stage and is expected to continue rapid vertical growth
- CThe anvil shape indicates the storm is isolated and poses no threat beyond its visible boundary
- DThe anvil indicates the storm has completely dissipated and no further hazards exist
Show answer & explanationAnswer & explanation
Correct answer: A. The storm has reached the tropopause, where stable air causes the cloud top to spread horizontally; hazardous turbulence and hail can still be thrown far downwind under the anvil
An anvil top forms when a growing cumulonimbus cloud reaches the stable air of the tropopause, causing the updraft to spread horizontally rather than continue rising. Strong upper winds can carry hail and turbulence far downwind under the anvil, well beyond the visible boundary of the storm, making this an area to avoid even though it may appear clear.
Why the other options are wrong
- B. An anvil top is characteristic of the mature stage, not the developing cumulus stage.
- C. Hazards like hail and turbulence can extend well beyond the visible storm boundary under the anvil.
- D. An anvil top indicates a mature, often severe storm, not dissipation, which is marked by weakening in the dissipating stage with predominantly downdrafts.
Cumulonimbus Anvil
A flat, spreading cloud top that forms when a thunderstorm's updraft reaches the stable tropopause, indicating a mature storm capable of throwing hazards far downwind.
- Marks the mature stage of a thunderstorm
- Formed by stable air at the tropopause halting vertical growth
- Hail and turbulence can extend far downwind under the anvil
Memory trick: The anvil spreads the danger far beyond the storm you can see.