11 degrees right now after a high of 15--the lowest maximum since last February. Granted, overnight lows are not as bad as the lows of 1 and 2 we had on a few days last winter, but a high of 15 is about as stiff as it gets around here. It's about as extreme as an overnight low of, say, 80. That's pretty extreme.

Why so cold? The new snow cover across the upper Midwest and central Canada. Arctic air masses can't moderate as they spread south. Air warms from thermal energy bounced off the ground, not directly from the sun. Snow acts to eat up solar energy instead of allowing it to reflect back up into the air, in effect preventing heating. As a result, temperatures as cold as -42F made it all the way down to Embarrass, MN two mornings ago.

Now attention turns to the possible coastal storm later in the weekend. Besides the usual debate about path and strength and precipitation type, I (along with some other weather friends) cannot understand why the National Weather Service seems to be ignoring the ECMWF (European) computer model. This model projects a major coastal storm off New Jersey by Sunday with each run taking it slightly closer to the coast. (Note that forecast times are in UTC, so subtract five hours for Eastern Time.) If the storm is too close, winds will come in off the ocean and the snow would change to rain.

The other major factor is a blocking high, or dense deck of cold air, over the Canadian Maritimes, which would force the storm to the south and shove it east-northeastward out to sea. I recommend bookmarking two excellent resources to follow the forecasting debates behind this storm: one of the National Weather Service NYC office (updated four times per day), and the other of WCBS meteorologist Jeff Berardelli (updated every day or so).