Are you dreaming of a White Christmas?

12/21/12  5:31 PM

CoAs an upper low lifts north into Canada, a stormy and cold weather pattern takes hold

I know what you are thinking.  Don’t pull my leg Steven.  A White Christmas?  A real one?  Yes, indeed the threat is there.

As my partners at Live Weather Blogs and Geo Environmental Atmosphere have shown, the models have all trended colder for the disturbance on Christmas morning and for the storm to follow around December 27th.  Oh, and another storm may be on the way around January 1, 2013 as well.  So the idea of a stormy and cold weather pattern is coming into play, just a week later than what was expected three months ago.

Now, all of my premium members know why the cutter idea supported by many models was an unlikely set up.  Basically, the idea of this upper low currently swinging through the Great Lakes this evening breaking down and collapsing was wrong.  Models typically break down these types of blocks WAY too fast and wouldn’t you know it, now that the models can gain from observational data of this upper level low, that now the trend is away from breaking up this upper low but simply shifting the upper level low towards the Canadian Maritimes and very close to 50N/50W.

This is all about physics and meteorological law.  That’s why the lake cutter idea was doomed to fail because a surface low can not cut up into a high latitude block.  That is just not going to happen.  Conversely, having two strong upper level lows in basically the same area as shown by the ECMWF last night was just not likely to happen as there was no building 500 MB heights to balance out the lower heights.  This is called Conservation of Mass, something had to give and it did with the 12Z runs today.  Now, whether the models make this error again is not important because we know what the correct solution should be and the storm track for the next several days based on the development of the upper level low over southeastern Canada.

Snow showers possible tonight

So let’s step back to tonight’s set up.  The upper low is lifting north and much colder air is invading from the west as temperatures crash through the 40’s and 30’s this evening.  Don’t be surprised if a few flurries or snow showers visit your local stomping grounds this evening as mid level disturbances rotate around this low and squeeze out the moisture in the atmosphere.  This upper level low will lift towards southwestern Quebec over the next 24 hours and set up the weather pattern for this weekend and for next week, which is on average cold.  Certainly colder than what we have been seeing.

On Monday, Christmas Eve, a strengthening disturbance will track towards the Delmarva Peninsula and begin to strengthen.  The low will strengthen because of the increasing thermal gradient between the cold land and the warm ocean waters.  Given the strength of the upper level low, look for a track from Delaware to just southeast of Long Island and towards Nantucket, MA.  This track will bring snowfall to the Philadelphia and New York City metropolitan areas.  How much snow will be determined by the boundary layer temperatures, the speed of the low pressure system, ability to intensify rapidly, and the development of a moisture transport circulation from the Atlantic.  These factors can not be accurately forecasted at this time, but the overall environment is favorable for accumulating snowfall from Philadelphia to Atlantic City, New Jersey and points north.

This Christmas storm will directly impact the track of the next storm for December 27th as this Christmas storm helps to enhance high latitude blocking over the northern Atlantic, thus enhancing high pressure over the St. Lawrence River Valley and supporting a track slightly further east.  This is starting to become more and more supported.  There is no point to go into details on what to expect for December 27th until we get the storm on Christmas nailed down.  However, I will say that the potential for significant accumulating snowfall for the entire northern Mid Atlantic, interior and coast, is growing with each passing hour.

Then of course we have another storm after this one.  See, I told you this winter wasn’t going to be like last year.

Well, plenty to keep an eye one.  I will have more updates when the time is reasonable to update.  In the meantime, get some Hot Chocolate and some yummy Christmas Cookies!