A few theories about the below normal temperatures...

[Stormsfury]

despite the overall pattern NOT conducive for such below normal anomalies.

Let's start with the Upper Air Conditions and Charts ... this runs from Dec 1st thru the 21st of December (and yes, it is a decent size loop ... about 4 MEGS).

http://www.stormsfury1.com/Temp/TempLoops/UAC.html

First of all, by now, everyone knows about the screaming PAC JET that's plagued the US from getting the REAL DEAL, so to speak. DT (WxRisk.com) had an excellent post about this before about the pattern didn't fit the temperature regimes.

I'll offer a few theories ...

1) The progressive fast flow didn't allow for any substantial warmups ... notice on the 850mb temperature charts and the upper level pattern. Notice just how fast the flow is across the US, so (unlike what we're seeing now, that dreaded SE ridge progged/up and coming), which kept carving out troughs across the east, and NO, it wasn't continuous troughing, it was little s/w disturbances carving out trough after trough in a very fast pattern. There simply wasn't enough time for a front in the warm sector to draw up a lot of warm air.

2) Particularly in the Southeast States, where the greatest temperature anomalies have shown up, I offer several hypotheses.

2a) The beginning of the month saw a nice CAD situation and held temperatures at bay and CHS has a prolonged period of below normal temperatures ...

2b) Secondly, there definitely hasn't been any stretches of warmer than normal conditions, and in fact, there's only been 6 days that have been above normal, and all, but 2 days, were BARELY above normal. Which leads me to theory ...

2c) Ideal Radiational Cooling setups on many nights. You can clearly see on the F6 Prelim Charts for CHS, that many days have extreme temperature swings from day to night.

http://wchs.csc.noaa.gov/fire/output_f6_KCHS

I haven't looked at many other prelim F6 data from other offices around but if you have the time, you might wanna take a look at those at your local NWS office and see if some of this is the case.

SF