Why Are Some Towns Always Cooler Than Others At Night?

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By Nick DiGiovanni on April 7, 2012, 1:47pm

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There can be an incredible range of temperatures between the towns in Connecticut. Usually, coldest temperatures are thought to be with the highest elevations in North-West Connecticut. To a certain degree, that is true; but there are other types of terrain that can get even colder than those NW Hills.

These areas are valleys. A valley is a lower area of land between the hills or mountains. But why do the temps fall 5-10 degrees cooler in the valleys than surrounding towns sometimes?

First off, you would need to understand convection. Convection means warm air rises and cold air sinks. Picture the letter "U"- the lowest part of the U is in the center (aka: the valley) the cold air sinking can pool and go there, because that is the lowest it can go.

Valley effect temps will not happen every night. The conditions needed for proper radiational cooling is clear skies, and no wind. When these conditions are conducive, the higher elevated towns tend to be the warmest. The most known valley is near Oxford and Southbury. There is a valley (Quinnipiac) that runs from New Haven to North Haven-Wallingford-Meriden-Berlin-Newington-Whethersfield-Hartford-Windsor Locks-Suffield, and all the way into Central Massachusetts. This is a thin valley, between 5-10 miles wide. Of all those towns listed, it is the suburbs that can get the coolest.

An example from the Quinnipiac Valley is that some mornings the temperature in North Haven (~75' elevation) may be 25 degrees, but 8 miles to the NW in a higher elevation, Durham (~500' elevation) may only be 35 degrees. Some Valleys can even run right near the beaches. There are multiple neighborhoods in Madison for example where cold air may pool in the lower neighborhoods away from the beach.

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Nick DiGiovanni

Town: North Haven, CT  

Reporting for WXedge since February 2012.

Articles: 84

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