Clear night sky and temperatures

[Tarmo Tanilsoo]

Hello there.

I have been noticing a strange phenomenon during past few days. Usually, a clear night means very cold weather at this season. However, something strange is going on this evening. Although it is clear outside, the air temperature still sits at 34 degrees Fahrenheit. At this season, with this weather, it should be already in 20's! We've been having hot weather with temperatures nearing 40 degrees Fahrenheit in some places during past few days and we are expecting brown Christmas... Second year in a row

Can anybody explain to me, why isn't the weather cooling down despite the clear night skies? This does not make sense to me. Any info is greatly appreciated.

 

[Karen Politte]

What is your humidity/dewpoint? It sounds like your dewpoint is too high - i.e. you have too much moisture in the your atmosphere - to cool below freezing.

Also - have you had windy conditions during these clear sky nights? Windy conditions will frequently stop the temperature from dropping.

KL

 

[Tarmo Tanilsoo]

Thanks for pointing that possibility out and indeed, it is so.

Just checked METAR data from Tartu-Ãœlenurme airport about 15-20 miles from my home and, yes, it appears that the dewpoint/humidity is the culprit:
2007-12-20 18:50 EETU 201850Z AUTO 26009KT 9999NDV FEW011/// 02/02 Q1019

About winds, yes, we had that last night:
Example: 2007-12-19 23:50 EETU 192350Z AUTO 25017KT 9999NDV FEW015/// 02/01 Q1018