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Leifie created the topic: Met Question
Q. An environmental lapse rate of 3°C/1000 ft is most likely to produce
A) Advection fog
C) A thunderstorm
D) Mountain waves
Answer is C Thunderstom
But I thought unsaturated air being forced aloft will cool at a rate of 3°C per 1000 ft so I don't understand why it's answer is Thunderstorm.
Unsaturated air cools at the dry adiabatic lapse rate (DALR) of 3°/1000ft. In this question the environmental lapse rate (ELR) is also 3°/1000ft. If a hot spot on the ground became 5° warmer than the surrounding surface, the air above it would reach the same temperature and begin to rise. The rising air would cool at 3°/1000ft and the environment through which it is passing would also be cooling at 3°/1000ft. So the rising parcel of air would remain 5° warmer than the environment air and would continue to rise. Given sufficient humidity, due point would be reached, from which point the saturated air would cool at only 1.5°/1000ft and so would become increasingly warmer than its environment and would rise even more rapidly. Hence a thunderstorm forms. If the surface air were forced to rise over a mountain or at a front the result would be similar once that air became saturated. There would have to be sufficient moisture however to form a cloud in the first place.
When an area forecast says visibility is 4000 SH/DZ/TS, it means that the visibility is forecast to be 4000 m if you are in the showers, drizzle or thunderstorms. However if you keep out of the showers, drizzle or thunderstorms, the visibility is forecast to be 10 km or better. See AIP GEN 3.5 para 3.6.4.
In this case, the TAF is irrelevant because the question asks what visibility is forecast in Area 22