Moisture will remain well entrenched for the remainder of the weekend for large swaths of the southern U.S.
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This will be particularly the case from the Southwest eastward toward the Lower and Middle Mississippi Valley, the Tennessee Valley, and the southern Mid-Atlantic region.
For the Southwest U.S., this moisture which is monsoon-driven will couple with daytime heating, upslope flow locally over the higher terrain, and also some weak energy aloft for broken areas of heavy showers and thunderstorms.
Very heavy rainfall rates are expected locally, and this will drive concerns for flash flooding with an emphasis on any of the more sensitive burn areas, slot canyons and normally dry washes which can fill up suddenly from heavy rainfall.
The Weather Prediction Center has highlighted a large area of the Southwest in a Slight Risk of excessive rainfall through the rest of the weekend to address the ongoing active monsoon season across this region.
The expanse of clouds and the threat of rain should keep temperatures also locally cooler and a bit below normal.
Meanwhile, for areas off to the east, there will be a very slow-moving front draped generally west to east from the Southern Plains east to the southern Mid-Atlantic region through Sunday which will act as a regional focus for areas of heavy showers and thunderstorms.
This will especially be the case as multiple waves of weak low pressure advance east along the front.
Given the amount of moisture that will be pooled along the front, very heavy rainfall rates will be likely, and there will be notable concerns for areas of flash flooding which include recently hard hit areas of the Tennessee Valley and southern Appalachians.
Locally a few inches of additional rain are forecast and the Weather Prediction Center has depicted a broad Slight Risk of excessive rainfall in the vicinity of this frontal zone to address the anticipated heavy rainfall.
Regarding the temperatures, just like for the Southwest U.S., the expanse of clouds and rain will tend to keep temperatures cooler and locally below normal.
This will especially be the case from the Mid-South to the Central and Southern Appalachians.
Showers and thunderstorms likely to develop across the interior Northeast and Southeast Monday night into Tuesday.
Elsewhere, a cold front will be advancing east across the Northern Plains and into the Upper Midwest today, which will bring a threat for some scattered showers and thunderstorms.
A few of the thunderstorms may be severe, and the Storm Prediction Center has depicted a Slight Risk of severe weather for parts of Minnesota and western Wisconsin given a threat for some large hail and damaging winds.
This front will bring some briefly cooler temperatures to round out the weekend for parts of mainly North Dakota and the Upper Midwest.
Excessive and record-setting heat is again expected to continue for the Pacific Northwest through today as daytime highs reach well over 100 degrees and nighttime lows drop only down into the upper 60s to low 70s.
Several record high temperatures are likely to be set and there are Excessive Heat Warnings and Heat Advisories in effect for a large area of the Pacific Northwest and extending east into the northern Great Basin.
The strong ridge of high pressure aloft that is responsible for this heat is expected to actually strengthen and expand eastward somewhat heading into next week which will allow for the heat to gradually rebuild farther east across the Central and Northern Plains. ■
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.