Monday, 11:55 A.M.
Though we're not finished with winter just yet, there are finally more and more signs that its days really are numbered. Look at the high temperatures from the northern and eastern Rockies out across the Plains on Sunday:
The warmth there yesterday will surge across the Mississippi Valley into the Ohio and Tennessee valleys today, and it will set the stage for a mild day from the Ohio Valley and mid-Atlantic states on south tomorrow. Here are the projected temperature anomalies tomorrow:
That's all well and good, but it still is winter, and we'll find out about that very soon; the next storm forming in the central Plains tonight will pull much colder air southward tomorrow, and that's going to translate into accumulating snow starting from parts of Montana and Wyoming, and then spreading out across South Dakota and Nebraska. As the storm gets better organized tomorrow, the snow will streak out across southern Minnesota and parts of Iowa, though points farther downstream will see that precipitation start out in the form of rain.
Part of the reason for that is the balmy air that moves in over the next 36 hours ahead of a cold front. That front will be slow to come south out of northern New England and upstate New York, and the surface storm will seek that boundary in the end. And that's why the rain-snow line ends up as far north as it will. Now the 12z NAM model has shifted that line even farther north. Look at the 850 mb temperature forecast for Wednesday afternoon:
Now, this is the same NAM model that only a couple of days before the storm of last Sunday night and Monday was trying to pull the same trick, and push the warm air very far north, and make the storm track far to the north. That couldn't have been further from the truth, as we all know where the snow ended up!
Still, there's more reason to believe this more northern storm track this time around, largely because of how mild the air mass will be tomorrow ahead of the storm, and where that true arctic boundary will set up. And here's the added key:
The storm itself will be more closely identified, at least to this point, with the lead feature that is crossing Ohio. There is a trailing upper-level trough coming in through the Midwest that will only add fuel to the storm and deepen it more rapidly as it helps to inject more cold air into the mix. That's how the rain changes to snow from west to east as the storm passes, though a scenario such as that will clearly limit how much snow can fall across the Ohio Valley into Pennsylvania. This would push the bulk of the heavy snow north into extreme northern and northwestern Pennsylvania and upstate New York and across much of Vermont, New Hampshire and Maine. Those areas could wind up with more than a foot of snow, and with a lot of wind on the back side of the storm to move it around quite a bit.
Another issue that will crop up is that of a flash or rapid freeze with the amount of cold air advancing across the Midwest and Great Lakes into the Ohio Valley, then the mid-Atlantic and southern New England. It could go from well above freezing with to below freezing with a little snow, and all that water not having a chance to dry off road surfaces before turning to ice.
Then, of course, there is the cold. It will be brutal, especially by March standards, on Wednesday in the Midwest, with highs in the teens and 20s. That will be the case in the Northeast and mid-Atlantic on Thursday, with highs only in the 20s and 30s across Maryland and a good chunk of Virginia. Place that up against normal, and you get this:
With surface high pressure along the Eastern Seaboard Friday morning, it will be a very cold start to the day! However, the good news is that the upper-level trough should quickly lift out to the east and northeast Friday in a fast flow aloft, so that the afternoon hours will recover nicely from the Ohio Valley to the East, and more so on Saturday ahead of the next cold front.
Take away this storm, and most of the week will be pretty quiet from the Plains to the West Coast. In fact, after a quick cooldown tomorrow into Wednesday over the eastern Rockies and western Plains, it should warm nicely on Thursday; temperatures in much of the West will be near to above average most of the week. And with each week, now, you can add 2 to 3 degrees to the average temperature in most locations. Normal looks pretty nice in a lot of places now, given how cold the winter has been!
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.
A dominant ridge will keep it hot from the Ohio Valley to the East into next week, while the disturbance north of Cuba is slow to develop as it approaches the southeastern Gulf of Mexico.