Friday, 11:15 a.m.
The waves of low pressure that are crashing into northern California and Oregon in one form or another are part of a pattern that is promoting unusual warmth across the Rockies and out onto the Plains right now, and that warmth will expand farther downstream this weekend.
Let me start with the morning surface pressure analysis and thickness across North America.
I chose this particular image because it is uncluttered by precipitation forecasts, making it easier to see the surface pressure pattern as well as the thickness lines. The things that stand out to me are as follows:
1) Very strong storm just northeast of Labrador;
2) The tight thickness packing emanating from this feature in an arc out into the northwest Atlantic, then back across New England and the upper Great Lakes;
3) High pressure still anchored over the Carolinas;
4) The big storm rolling around the northeast Pacific;
5) The lack of chill over the West and Rockies to the Mississippi Valley.
Of all these features, the one currently in charge of the chill in the East is that storm off the coast of Labrador. As it weakens and moves away toward the southern tip of Greenland this weekend, it pulls the chill off the table, and there's none to replace it. As a result, the clockwise flow around the high over the Carolinas will pump the warmth from the Plains and Mississippi Valley into the Ohio and Tennessee valleys, as well as the Great Lakes. It may take some time to get fully into the mid-Atlantic and especially the Northeast, but even in these areas it will be a lot warmer Monday than it is today, plain and simple.
The effect of this warming will be enhanced as the storm that crashes into northern California tomorrow night with flooding rain and heavy mountain snow ends up redeveloping over Montana and southern Saskatchewan by Sunday night:
Look at the resulting temperature anomalies for Monday across the country:
The interesting thing about that storm and the cold front it will drag across the Plains and Midwest Monday and Monday night, then off the East Coast by Wednesday morning, is that the air behind it won't really be cold. Look at the storm track - northern California to southern Saskatchewan, then across northern Ontario to northern Quebec. Initially the air is purely Pacific in nature coming through the Northwest and northern Rockies. With time, it'll start to draw a little arctic air out of western Canada, and there will be a more noticeable impact on the temperature changes farther downstream. That said, it's still going to be balmy in the Plains during the middle of next week, as there just won't be any arctic air or any snow cover there.
That will lead to another surge of much above-normal warmth coming out of the Plains and heading into the Ohio and Tennessee valleys during the second half of next week, reaching the East next weekend. The end result will be a very, very mild week to open up December. Look at the projected GFS seven-day ensemble means from tomorrow through next Friday:
Not exactly a wintry start to the winter season!
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