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Name: Sarah R Atchley
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Question:
From a weather unit: Are summer clouds different than winter clouds? We took into consideration angle of refraction, absolute humidity...but the basic question remains: what about conformation? We (Massachusetts folk) cannot remember many thunderheads in winter, but could not find a clear, convincing answer.



Replies:
The atmosphere is generally more unstable in summer in the middle latitudes (including much of the United States) so we have more thunderstorms in the summer. The atmosphere becomes more unstable when heat and moisture increase in the lowest part of the atmosphere. So towering cumulus clouds are much more common in summer when warm humid air masses can spread north from the Gulf of Mexico or the Atlantic into the central and northern United States. We can get thunderstorms even in winter if a strong enough storm system can transport tropical air far enough north.

In winter often cold air masses spread over the north and central United States. Since cold air is more dense than warm air, cold air hugs the ground. When warm air moves in it often rises above the cold air mass. Sometimes flat layered stratus or stratocumulus form in these weather patterns. This is known as an inversion. The low sun angle and short days do not allow enough heat to break the inversion in winter but the sun can usually break a summer inversion. Early morning fog or stratus often burns off or turns into fair weather cumulus in summer but it may persist all day in winter.

Allsopp



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