Wednesday, 11:55 a.m.
The storm that brought upward of a foot of snow to parts of the mid-Atlantic and southern New England in the past 24 hours. That storm is now largely over with, though it is still snowing pretty hard with fierce winds over southeastern Massachusetts at this hour. Here's the late morning visible satellite image of the region:
Notice the white in that image? Very little of it is associated with cloud cover! It's pretty much solid snow cover, and it's a snow cover that's not going to magically melt away in the next couple of days! There's plenty of arctic air to be had, now, and it's still January. That means the sun angle, while gaining about a degree of altitude every four days, is still low to really have a direct on melting snow, especially if the dew points are below freezing. That's more than a given in this gelid air mass!
Let's face it. The pattern is a cold one, and it is going to be stay that way for a while. In fact, the cold will be expanding in time to the west. The eastern Rockies will get a brief and glancing blow of that cold in the next 36 hours as a front backs in from the the north. Let's examine the 12z Jan. 22 NAM model surface forecast for this evening:
The first feature I want to draw your attention to is the surface low moving into Michigan this evening. The air mass south of the track of this low, while very, very cold, is still managing to best the 'numbers,' if you will. It's not so much in terms of how high the temperature is getting across Wisconsin and Illinois into Michigan today, but more in terms of forecasts yet again being to quick at pulling temperatures down in the arctic air. Anyway, there is some snow with this low, but it is hardly heavy. The 'fluff factor' is high, though, so a tenth of an inch of liquid could easily yield 2 inches of snow across Wisconsin and Michigan this afternoon, and into the Ohio Valley later this afternoon and tonight. Compared to what just fell in the mid-Atlantic and southern New England, and what can often happen in these areas in winter, this is probably considered little more than a 'flurry.'
Arcing out of this low is a bona fide cold front that by 0z will be south of Kansas City and will be approaching Denver from the north and northeast. You'll also note the stripe of printout on the model this afternoon from south-central Montana to southern Wyoming, a band of snow that will streak south-southeastward into Colorado tonight along the Front Range. Again, in terms of snowfall amounts, maybe a few inches in some locations, but most will do well to get an inch or two.
Lastly from the image above, see the strong surface high building into western North Dakota? That high is driving another bitterly cold air mass into the northern and eastern Rockies and northern Plains as we speak, and it will deliver a quick-hitting shot of very cold air to the eastern Rockie and western Plains tonight and tomorrow before it is modified rapidly on Friday behind the high.
Now look at the same model forecast for Friday morning:
The surface high will have dropped into the lower Mississippi Valley and southern Plains, and it will be overrun by some moisture coming out of the eastern Pacific and across Mexico into central and southern Texas. Don't be surprised by some ice and snow in the Hill Country tomorrow night into Friday, fanning out across central Texas to almost Dallas.
While that is unfolding, look at the strong chinook winds roaring across the northern Rockies and up into Alberta and southern Saskatchewan. Even farther north we find a powerful storm roaring across Hudson Bay, and it will help to generate a lot of strong winds Thursday night and Friday from the northern Rockies eastward into the Midwest and even the Ohio Valley!
As we have seen with every single one of these waves of low pressure, temperatures will invariably end up higher than forecast across the northern Plains into the Midwest. And they'll stay up a few hours longer that predicted as well. This milder air will sneak into the Ohio Valley Friday afternoon, though it will hardly be considered 'mild' at that time, as temperatures will still be quite a bit below average. In addition, the combination of cold air and strong winds will still lead to very low wind chills.
The milder air won't just advance in from the west and take whatever territory it wants without facing some resistance! Snow is going to fall, and it will come in two ways. The first will be the simple act of warmer air gliding up and over the low-level dense arctic air, leading to an area of snow from northeastern Minnesota to northern Michigan.
The second area of snow will come as a little wave of low pressure forms along the arctic front and slides across the Upper Midwest Friday afternoon, and into the Great Lakes and Ohio Valley Friday night. South of this wave, the air will get surprisingly mild, and it wouldn't shock me if the southern edges of the precipitation shield wasn't entirely snow! Within the snow area, though, a few inches can easily accumulate. Here's the NAM projected QPF from Thursday evening through Saturday evening:
It isn't a classic Alberta Clipper, but it may have the same effect as one, resulting in a decent-sized area of 2- to 4-inch snows, with locally 6"+ amounts before all is said and done behind this wave Saturday evening. It should be noted that little of this moisture makes it over the Appalachians into southeastern Pennsylvania, Delaware, Maryland and points south. By the same token, these areas, despite limited sun on Saturday, will challenge normal highs in the afternoon and could even exceed them in a few places by a couple of degrees.
Right on the heels of that front will come more arctic air. Even as it is charging to the mid-Atlantic coast and New England Saturday night, a new wave of low pressure will move into the Dakotas by Saturday night. The 12z GFS has come in and has adjusted its track of this wave farther north to more closely match the tracks of the 0z Canadian and European models. It now send the low into Iowa by Sunday morning:
Once again, there will be a nice surge of mild air coming across the Plains to meet this low, so don't be surprised by a nice jump in temperatures Sunday from the central Plains to the central Appalachians south of the track of the low. This one, by the way, will be much more your classic Alberta Clipper - a tightly wound, small storm with a lot of punch, generally quick-hitting in nature. The core of the snow will be from 50 to 125 miles north of the track of the low, and that means the central and eastern North Dakota into southern Minnesota, Wisconsin, northernmost Illinois, southern Michigan, northern Indiana, and northern Ohio are looking at a good 3- to 6-inch snowfall, with locally higher amounts. That snow that moves across northern Pennsylvania and upstate New York later Sunday and Sunday night, and on across central and northern New England Sunday night.
The surge of mild air will diminished somewhat east of the Appalachians Sunday afternoon as the arctic will have just arrived Sunday afternoon. Then the arctic front with this clipper will pass through, bringing an even colder air mass into play from the eastern Rockies all the way to the East Coast to open up the last week of the month. I don't think the GFS ensembles have quite caught on to how nasty this air mass is going to be and how far west it will stretch, but it is coming around. Here's its forecast for Monday:
As we go deeper into next week, there will be some changes in the pattern as the seemingly permanent western ridge finally breaks down, but the cold won't go away from the East all that easily.
Two systems will delay the onset of warm weather in the Ohio Valley and the East over the next week or so, but then it should get warm all across the country heading into the Memorial Day weekend.
A turn to much colder air over the Northeast and mid-Atlantic states will set the stage for a rain and snow storm later this weekend before it turns much warmer later next week.
It's warm now, but will turn much colder this weekend, with a storm threat later Saturday into Sunday. Warmth will return by the second half of next week.
Though it is cold now east of the Mississippi, with a couple of opportunities for snow into the weekend, a blast of warmth is due for much of the country east of the Rockies next week.
Warm air will once again surge eastward from the Plains to the East Coast this weekend and early next week. A strong storm next Tuesday and Wednesday will then be followed by colder air later next week.
A storm in Southeast Texas will generate severe thunderstorms this afternoon and tonight, and some wet snow on its western flank as it heads into the Ohio Valley tomorrow.