Tuesday, 11:55 a.m.
I think I can safely say that the worst of the bitter arctic air that has been so prevalent for much of the winter season will be behind us late this week. Does that mean winter is about over? Ha! Hardly! No, it just means that the all-time March record low temperatures set in Baltimore and at Washington's Dulles Airport this morning are highly unlikely to be approached again the rest of the cold season. That said, it is not a time to break out the shorts and suntan lotion if you live from the northern Plains and Midwest to the northern mid-Atlantic states and New England! Most of these areas will not just be below normal much of the next two weeks, but many days will be much below average!
In the wake of the snowstorm that hit parts of the mid-Atlantic yesterday, high pressure has built over Pennsylvania and Maryland, and that promoted a clear sky with light winds overnight. If you look at the 700 mb heights and relative humidity forecast for this evening, you can see the makings of another surge of bitter, arctic air to come out of Ontario and Quebec:
The areas shaded in green represent some moisture and very weak disturbances that will spit out a little snow here and there, but none of it will be heavy. By tomorrow night, that will all be gone, and another strong arctic high will be heading toward the Northeast:
What this means is that most places from northern Virginia and Maryland on north will be no warmer Thursday than tomorrow, and, indeed, could be a little colder. It also sets the table for increasing winds along the Eastern Seaboard Thursday, as the high builds in to the north, while the pressure begins to lower along the Southeast coast.
That will take place as a result of a one-two punch of upper-level disturbances coming through the South. The first of these has already caused a lot of problems in central and southeastern Texas overnight and this morning. Arctic air overwhelmed the state over the past couple of days, all the way down to the Rio Grande Valley. Temperatures around and particularly west and northwest of Houston were below freezing as rain and sleet broke out, making for an extremely treacherous time of it. This lead disturbance will move east-northeastward across the northern Gulf this afternoon and tonight, spreading rain across Louisiana to the Florida Panhandle, including the southern half of Alabama and Georgia into South Carolina overnight into tomorrow morning.
A second disturbance is coming across the central Rockies now and will generate a short period of snow tonight in Denver, that after a mild day. That upper-level trough will dig southeastward into Texas tomorrow, as shown by the NAM 500mb forecast tomorrow evening:
In turn, this will cause more rain to break out tomorrow night into Thursday from the lower Mississippi Valley on east, with low pressure eventually forming over the north-central Gulf by Thursday. As the trough slides eastward Thursday, the low will eventually reorganize off the Southeast coast Thursday night, so with the high building in to the north, the wind will get stronger along the mid-Atlantic and Southeast coast.
The storm will spread rain so far north in the East before the whole storm escapes offshore later Friday and Friday night into the start of the weekend. Can there be some snow? Yes, there can be! However, it will be in limited areas, primarily over the western Carolinas and northeastern Georgia, and especially in the higher elevations. Most other locations, while cold and wet, will not be quite cold enough to support snow.
North and west of the storm, it will warm somewhat on Friday, but over the Ohio Valley and central Appalachians to the northern mid-Atlantic, there won't be a lot of wind, so a temperature inversion will set up that will prevent the warmer air aloft from reaching down to the surface. This effect will be even greater over the fresh snowpack.
Father north and west, there is still more arctic air. Another weak storm will cut across the Upper Midwest and head for the northern Great Lakes on Friday, pulling a cold front southward. High pressure will build into the northern Plains behind this front to push another very cold air mass along. The GFS ensemble temperature anomaly forecast for Saturday suggests a cold start to the weekend form the Dakotas to the Great Lakes:
This same front should sail across the Northeast Saturday with little fanfare, only for another upper-level trough to follow it quickly Saturday night and early Sunday. The net effect is to trim back the gains made ahead of all this from the Ohio Valley to the mid-Atlantic states and New England Friday and Saturday.
That's just into the weekend. Would you like to see more cold? Oh, there's plenty more where it came from for next week. Now, as I stated earlier, this cold is highly unlikely to match or even rival the current bitter, arctic air mass that is in play. That said, there's every reason to believe it will mean cold to start next week from the Great Lakes to New England. Once a storm passes by during the middle of next week, another cold air mass is likely to charge southeastward east of the Mississippi for the second half of next week.
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