The exception weather that pushed into the Mid-South this weekend will linger through the first half of the week.
A light north breeze will keep the humidity low, as dewpoint temperatures will only be in the upper 40s on Monday and Tuesday afternoons. That's a far cry from the muggy 70-degree dewpoints we often Tennessee often faces this time of late summer.
The first image shows predicted high temperatures from the GFS computer model for this afternoon. A big push of 70-degree temperatures is in place from the Upper Midwest through the Northeast, and that extends as far south as parts of Kentucky.
The cool air at the surface is reflected in the upper-level trough that dips across the eastern half of the country. You can see that in the second image, which is the GFS forecast for the 500 millibar level, up around 18,000 feet aloft. While the eastern U.S. enjoys a respite from the heat, there's a corresponding hot ridge of high pressure across the western U.S. where surface temperatures are in the 90s and 100s in the interior valleys. Meteorologists refer to this amplified upper air pattern as meridional, in reference to lines of longitude, which are called meridians.
Of course, late August Tennessee temperatures in the 80s won't last forever. Take a look at the third image and you'll see that by Friday, surface temperatures are forecast to return to near-average, which means close to 90 degrees. A few days of a south wind will bring a return of muggier conditions by the weekend.
The corresponding Friday upper air pattern (fourth image) depicts a more zonal flow, which means less north-to-south amplification and a more west-to-east flow. When the South finds itself under zonal flow, temperatures are usually at-or-above average down at the surface.
The moral of this weather story? Enjoy the cooler-than-average temperatures courtesy of our amplified weather pattern while they stick around!
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