Tuesday, 11:45 a.m.
If you look at the weather map today across most of the country, there really isn't a lot of cold air around. In fact, if you study it very closely, you'll note that the air mass stretching from southeastern North Dakota and eastern South Dakota eastward through the Great Lakes into most of New England is NOT cold. Certainly not cold by recent standards and really only marginally cold enough to support snow. Here's the 12z March 11 NAM 850mb forecast for 18z this afternoon:
It is turning colder in the northern Plains and northern Minnesota behind a cold front of sorts, as the dew points and temperatures have come down steadily since the pre-dawn hours. And you can kind of see where that boundary is on the 850mb forecast, stretching from northeast Lake Superior and the Upper Peninsula of Michigan to the border of North Dakota and South Dakota. The air mass behind this boundary IS cold enough for snow, and it's not even the really cold air that is amassing farther north in Ontario and Manitoba.
If you want to see where the surface storm is now, here's the 15z surface pressure analysis:
Currently the storm is a 996mb low in central Kansas, but as it moves eastward tonight and tomorrow, it will steadily deepen, especially tomorrow. The contrast in air masses from one side of the storm to the other will grow larger and larger. The NAM model forecast of temperatures just off the ground tomorrow afternoon is quite striking from the I-95 corridor to Lake Erie:
That will help to deepen the storm, and accelerate the process of drawing much colder air southward behind the storm.
It should be noted that the feature currently in the Gulf of Mexico will not play a pivotal role in the development of this storm. SOME of the moisture will be handed off to the northern branch feature, but not all of it. That will lead to an area along the Eastern Seaboard that will not see much precipitation at all from this storm. Here's the model forecast of total precipitation through 0z Thursday:
Basically, the only precipitation that is likely to occur from southeastern Virginia to southern New Jersey will be with the front early tomorrow night - a couple of showers, maybe a gusty thunderstorm, and then it's over. The southern stream system just won't contribute a lot of moisture to the bigger storm passing by to the north.
Now, where it is all snow, there may be a LOT of it. Look at the same chart, running from 6z tonight to 18z Thursday:
It's probably NOT going to look exactly like that, but if we assume that the total precipitation is even 70 percent to 80 percent is what being forecast, and at a ratio of 10 inches of snow equals 1 inch of water, you could be looking at 20 inches or more of snow from the Mohawk Valley to interior southern Maine! here's some of the latest thinking at AccuWeather.com on snowfall totals:
Again, it probably will look a little different in the end, but it's going to be a wild storm in some areas from northern Illinois all the way to central and especially northern New England. Perhaps another aspect of the storm will be the rapid drop in temperature behind the front, going from far above freezing to well below it in just a few short hours. When you combine that with lingering moisture from the rainfall, then there's a valid concern of a rapid freeze up from the Ohio Valley to the mid-Atlantic into New England. That includes your car doors!
Regardless of the amount of snow that does or does not fall, it will turn bitterly cold for about 36 hours behind the storm. Temperature departures will be more than 20 below normal Thursday, with record lows likely in a number of places. Then, after a cold start to Friday in the East, the moderation process will begin in the afternoon, and will lead to a relatively mild start to the weekend before the next cold front blasts through the Great Lakes and Ohio Valley into the Northeast.
Heavy rain will soak drought-stricken areas of the mid-Atlantic over the next couple of days. Focus will then shift to Matthew and its potential to impact the Eastern Seaboard with more heavy rain later next week.
Summer has ended astronomically, but from a meteorological standpoint, there's plenty more warm weather heading into October from the Plains to the East.
Two strong cold fronts will charge across the country in the next week, eventually taking out the current hot and humid air mass from the Plains to the East Coast.
Over the next three days, hot and humid air will expand across the Mississippi Valley all the way to the East Coast. This will be followed by even more heat and humidity leading into the weekend.
Hermine will head across the Florida Panhandle late tonight, then cut across the coastal Carolinas and become a headache for the mid-Atlantic and southern New England over the Labor Day weekend. It will be followed by a heat wave later next week.
The heat and humidity will be erased from much of the East later this week, but warmth will spread from the Plains eastward over the weekend. The tropics could still play an important role in the weather along the Eastern Seaboard this weekend.