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KateM created the topic: Question 2 in the 3rd CPL Met prac Exam
The question about a prerequisite for the development of a thunderstorm, it says the answer is it needs to be conditionally stable atmosphere, but from what I read in the book its supposed to be conditionally unstable. the answer given is: The conditions necessary for the formation of a thunderstorm are:
1. Conditionally stable atmosphere.
2. High humidity.
3. A trigger mechanism to begin the initial lifting of the air.
Conditional stability exists when dry air is stable but saturated air is unstable. That is, rising air that doesn't form cloud will eventually stop rising and cause no real problems for a pilot. However, once cloud begins to form, the cloud will become unstable and rapidly grow to form a large cumulonimbus cloud.
The correct answer is: a conditionally stable atmosphere
So just wondering which one is the correct answer?
Carello replied the topic: Question 2 in the 3rd CPL Met prac Exam
Condition stability is as you described. The atmosphere is stable if the rising air parcel is dry but unstable if the rising air parcel is saturated. In short, "conditionally stable" and "conditionally unstable" mean the same thing.
The atmosphere is "conditional stability" when the ELR lies between the dry adiabat and the moist adiabat - see diagram below.
To get a thunderstorm you need three ingredients.
1) you need atmospheric instability - absolute instability or conditional instability
2) you need fuel (water vapour)
3) you need a spark (a lifting mechanism).
That means answers 1, 2 and 3 are all technically correct - something to think about.