Lets take a detailed look into our upcoming thaw: As early as tonight, you will be able to see the beginning signs of pattern change. Below is an image showing that overnight, and into tomorrow, the winds will shift out of the Southwest, and eventually the South. This will be early insight into a much bigger picture that will be our upcoming thaw.
Now your probably wondering: What forces at work will bring us out of the deep freeze that we have been in the grips of for the better part of December? Why are the winds shifting out of the South? How are we going from single digits and subzero temps, to highs that may hit 60 if the models are correct? Let me explain: the answer is high pressure. This will create a ridge in our jet stream, resulting in warm air from the tropics hitching a ride straight to the Hudson Valley. The flow around a high pressure system is clockwise. So, if there is a high pressure system sitting to our southeast, what direction would our winds be coming from? If you said the South; you are correct. In the next image you will see the high pressures responsible for this warmer weather drifting east of the Carolina coast towards Bermuda. You will also see all the lines around the high pressure system. These are Isobars, and they connect equal lines of air pressure. You can use those lines to imagine the clockwise flow around the high pressure, and how it is basically natures the idea of turning up the thermostat.
The next question: Just how warm will it get? Lets see if the European weather model can give us some insight into that question… In the following five images you will see the European model’s forecasted max temps for each day. You can see how gradually warmer air fights its way north, thusly pushing the max temps up each day. As long as we are under the influence of that southerly flow, the cold air and snowpack will be fighting for its’ life. You must keep in mind that the model may be a bit overzealous on these temps, and may be underestimating the effect a deep snowpack can have on air temps; but no matter how you slice it, you will be seeing much milder weather Friday into Monday.
Visible in the projected five day max potential temperatures, we definitely have a warm-up coming our way. The snowpack will have to fight hard if we are going to pull off a white holiday. Not to mention, we will also be dealing with a period of potentially heavy rainfall Saturday night into Sunday. It’s important to clear your gutters and storm drains before this potential rainfall. The warm up doesn’t appear to have much staying power; it seems temps will be back to average by Monday night and right through Christmas.
(Images used with permission from Dr Ryan Maue of Weatherbell)