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Upper-Level Ridge Will Determine Who Gets the Heat

August 26, 2013; 9:11 AM ET

Monday, 11:30 A.M.

Summer is FAR from done. Feast your eyes on Sunday's highs:

That's a lot of places from the Mississippi Valley to the eastern Rockies, and from the southern Plains to the Canadian border that hot 90 or better on Sunday, with a few places reaching the century mark. This ridge isn't going anywhere, and it is slowly but surely drying out the atmosphere across the central and southern Plains to the Tennessee Valley and much of the South. In fact, the 12z Aug. 26 NAM total precipitation forecast through Thursday shows a large area of the country devoid of any kind of precipitation:

The middle of the country will simply bake all week long, and that includes the Mississippi Valley and adjacent areas of the western Ohio and Tennessee valleys. As the week wears on, it will get progressively hotter, with 100-degree readings likely to be seen in parts of the interior South and southern Plains by Wednesday or Thursday. They won't be widespread, mind you, but they will show up.

The heat will try to expand into the East, but with far less success, at least initially. The position of the upper-level ridge, and its structure, simply won't allow it to come bodily eastward. Here's the latest NAM 500 mb forecast for tomorrow evening:

Thunderstorms forming at the apex of that ridge will head downstream, and that means following the upper-level flow southeastward. One round has moved out of the Lakes into the Northeast overnight. Another is now in northern Wisconsin and northern Michigan, though its clearly weakening. Still another will develop in the next 24 hours and head southeastward, all of which will have the effect of cutting the heat off at the past for several days.

Eventually, though, the upper-level flow will flatten over the weekend, and SOME of that heat will be allow to come farther downstream. What remains to be seen is how much of it can survive over the Appalachians into the East later in the Labor Day weekend, and what role thunderstorms may play, if any, in keeping it from getting to the 90s.

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

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Joe Lundberg
Joe Lundberg, a veteran AccuWeather.com forecaster and meteorologist, covers both short and long-term U.S. weather on this blog.