The upper level pattern through mid-week features a pair of upper level ridges; one over the Southeast and another in the Pacific Northwest.
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Both are responsible for their own respective areas of excessive heat.
This has resulted in numerous Excessive Heat Warnings and Heat Advisories being issued in portions of the Lower Mississippi Valley, the Southern Plains, and throughout much of the Pacific Northwest.
Daytime highs are forecast to soar into the triple digits in the Columbia Basin and central Oregon, while the Seattle and Portland metro areas reach the mid-upper 90s through Thursday.
Daytime records highs will be challenged each day as well.
In the South-Central U.S., oppressively higher dew points leads to sultry heat indices as high as 110 degrees.
The Southern Plains and Lower Mississippi Valley are to remain mired in stifling heat until late week when a cold front brings much needed relief in the form of cooler temperatures positioned in the Midwest.
The ridging atop the Southeast will keep hot and humid conditions in the forecast with temperatures growing increasingly hotter up and down the East Coast by Thursday.
The coolest temperatures will be found in the Great Lakes, Midwest, and Southwest.
In terms of precipitation, this evolving upper level pattern is ripe for rounds of heavy rainfall and strong-to-severe thunderstorms.
A Bermuda High and troughing in the southwest will direct both Gulf of Mexico moisture and monsoonal moisture east into the Middle Mississippi Valley and on east to the Ohio Valley and central Appalachians.
These moisture sources are set to overrun a stationary front setup across the east-central U.S. and act as the catalyst for seemingly endless rounds of showers and thunderstorms through the remainder of the work-week.
Some of these thunderstorms could produce flash flooding, especially in the Middle Mississippi, Ohio, and Tennessee River Valleys.
WPC has issued a Slight Risk (threat level 2/4) for much of the Ohio Valley and into the central Appalachians today.
By Wednesday, an even deeper plume of atmospheric moisture and added upper level support aloft sets the stage for an even more favorable environment for torrential rainfall.
With soils growing increasingly saturated with each passing day as well, soils will struggle to keep up with the anticipated excessive rainfall rates in parts of the Ohio Valley.
As a result, a Moderate Risk (threat level 3/4) has been issued for central West Virginia on Wednesday, along with an expansive Slight Risk area threat stretches from the Ohio-Mississippi Confluence to the Laurel Highlands of southwest Pennsylvania.
this stagnant pattern, causing a fire hose of bountiful atmospheric moisture, will continue stick around into Thursday where yet another Moderate Risk is out for parts of West Virginia and eastern Kentucky, while the Slight Risk area includes much of the Tennessee Valley.
Farther west, the Southwest will continue to witness its deluge of monsoonal moisture stream over the region, prompting the daily development of heavy showers and thunderstorms throughout the region.
A large Slight Risk is in place for much of the "Four Corners" region both today and Wednesday.
Areas most vulnerable to flash flooding remain areas near burn scars, in slot canyons, in locations that have overly saturated soils, and in more heavily urbanized areas of the Southwest.
Flood Watches remain out for much of southern and western Arizona, as well up into southern Utah. ■
A clipper system will move quickly across the northern Plains into the Midwest Friday and the Northeast by Saturday, bringing a wintry mix of rain and snow showers ahead of a sweeping cold front.