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Why was last night so cold?

Last night was cold, really cold.. When I got home from work this morning, it was a bitterly-cold -4 Fahrenheit. So, with last night being a prime example of a cold winter night, many people are asking a question: why was it so doggone cold, anyway?

Short answer: radiational cooling. Extended answer, read on.

All the time, day or night, the Earth radiates heat. During the day, though, all of the energy from the Sun coming to Earth far outweighs any heat radiated back into space by our planet. Net result: with more energy coming in than being lost, the temperatures rise. At night, there is obviously no solar energy coming in to warm the atmosphere. So, with energy escaping into space and none coming in from the Sun, the result is a cooling atmosphere.

Now, the amount of cooling experienced depends on a lot of factors, including but not limited to humidity, snow cover, and the length of the night. However, the biggest factor is whether there are clouds or not. If there's a cloud deck overhead, that heat radiating from Earth wants to rise, which it does. Problem: with a thick deck of clouds in place, that heat is reflected back down to us, thus keeping the air warm (warm being a very relative term in the Cleveland area this time of year).

Now, take away the clouds and one sees perfectly well why clear Cleveland nights in winter are so cold: no clouds, no heat reflected back to Earth, cold nights.

The good news: the Cleveland area forecast is calling for moderating temperatures in the coming days, with a high temperature of 18 today with a low of 10 tonight. By the weekend, optimistic forecasts predict highs in the mid 30s.

Gotta love Cleveland weather!

For more info:
More about radiational cooling
Why layering keeps you warm

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