A significant heavy rainfall event is forecast for the Southwest as a mid-level low and anomalously high moisture associated with a remnant tropical wave help to enhance storm development associated with an already active monsoon.
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There is a Moderate Risk of Excessive Rainfall Friday and Saturday for portions of southeastern Arizona and southwestern New Mexico.
Daily areal average rainfall totals of 2-3 inches, with locally higher amounts approaching 5-6 inches, may lead to numerous instances of flash flooding.
Slight Risks for Excessive Rainfall are also in place for a broader area into the Four Corners region Friday and the Southern High Plains Saturday as additional scattered instances of flash flooding are possible.
Areas of complex terrain, slot canyons, arroyos, and burn scars are at an increased risk for flash flooding.
Meanwhile, to the west, hot weather will persist from California northward into the Pacific Northwest under the influence of an upper-level ridge.
Numerous heat advisories are in place as temperatures are forecast to reach into the upper 90s to low 100s Friday for portions of the interior Pacific Northwest and northern Great Basin.
As an upper-level trough approaches from the west, temperatures will cool a bit Saturday but still remain hot with highs in the low to mid-90s.
Further south, highs will remain hot through Saturday in the central valleys of California with low to mid-100s expected.
Widespread showers and thunderstorms are expected along a wavy, stationary front stretching from the Southeast into the Southern Plains and also with a frontal system moving from the Northern Plains into the Midwest into the weekend.
The greatest chance for some scattered instances of flash flooding will be for coastal South Carolina Friday.
Otherwise, only isolated impacts are expected.
Elsewhere, well below normal high temperatures in the 70s to low 80s are forecast for most of the Southwest, Great Basin, and Southern Rockies due to the widespread clouds and rain.
Below normal highs are also forecast Friday for the Southeast (low to mid-80s) and for the Northern Plains (low to mid-70s), with temperatures increasing a few degrees closer to normal Saturday.
Hotter temperatures in the upper 80s return to the Mid-Atlantic and New England with otherwise tranquil conditions expected. ■
A hyperactive weather pattern will bring an expansive low pressure system across mainland U.S., resulting in widespread impactful weather to progress from west to east across the country through the next few days.