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    Joe Lundberg

    Retreat From the Chill

    10/09/2012, 7:26:13 AM

    Tuesday, 11:15 a.m.

    The second shot of chilly air is now invading the northern and eastern Rockies and northern Plains behind another cold front, and that's clearly shown by the 24-hour temperature change from yesterday morning to this morning:

    By the same token, the chill that invaded the South over the weekend is now in full retreat.:

    The warming that is now underway across the southern Plains will be briefly trimmed by the passage of a cold front tonight and tomorrow, and only into Oklahoma and far northern Texas. With the second front moving into the northern Plains late tomorrow and high pressure quickly sliding into the Ohio and Tennessee Valleys tomorrow night, the southern flow from the Gulf of Mexico will resume and expanding, chasing that brief shot of chilly air away starting on Thursday.

    Before the first front clears the Northeast and mid-Atlantic coastline late tomorrow, there will be a little more moisture to contend with. Some of it will be from a return of marine air or, more properly, the addition of warmth to an already moist air mass from eastern Virginia up into New Jersey and eastern Pennsylvania tonight and tomorrow. That'll lead to some low clouds and fog and even some drizzle at times that can break for some sun tomorrow afternoon, especially south of the Mason-Dixon Line.

    The second source of moisture will be with the front itself. There are some showers now from parts of southern South Dakota and northern Nebraska across northern Iowa into southeastern Minnesota and Wisconsin. These showers will attend the front as it crosses the rest of the Midwest and mid-Mississippi Valley into the Great Lakes and Ohio Valley, but the showers will tend to diminish tomorrow as the front crosses the central Appalachians into the mid-Atlantic. They will, however, hold together into New England.

    With the second front, there will also be a little shower activity, but even less than with the first front. Most of it will slide across the Upper Midwest into the Great Lakes, where it may mix with snow, believe it or not!

    Following this latter front, a large surface high will move down into the Midwest Thursday night, resulting in widespread frost. That same high will end up over the mid-Atlantic and Northeast Saturday morning, with more frost likely from the Susquehanna Valley to the Delaware Valley and much of interior New England.

    Once we get past that chilly morning, mild air will really start to expand.

    The key to this change will be the upper-level low moving from just off the California coast today to southern California by late Thursday. From there, a strengthening of the Pacific jet upstream will cause this upper-level low to be pushed more forcefully to the east and northeast Friday into the weekend. In turn, the upper-level low will open up, sending a storm out across the Plains toward the Upper Midwest.

    In response to all of this, the heights will steadily rise over the Gulf of Mexico, and by Friday evening, it is pretty clear there will be a nice ridge popping up across the Mississippi Valley:

    Look, then, at the contrast between the last of the chilly air masses over the Northeast and the advancing and expanding warmth on Saturday:

    With no downstream blocking and a strong Pacific jet finally sending some long-lost moisture at the Northwest beginning later Friday and lasting through the weekend, there will be a complete erasure of the chilly air masses that had invaded the northern Plains and northern Rockies. So, in the wake of the weekend storm, cooling will be minimal.

    That will set the stage for a notably warmer pattern throughout the South and into the East through at least the middle of next week, perhaps even longer.

    Perhaps lost in all of this is that line above - some long-lost moisture finally moves into the Pacific Northwest. It has been extremely dry since the middle of the summer, and even though much of this moisture will left for western Washington and portions of western Oregon, any moisture that survives over the Cascades into the eastern parts of both state will be welcome. The wettest period appears to be set for later Sunday into Sunday night, with a couple of inches of rain could pelt the Northwest coast.

    The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com


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    Joe Lundberg