Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 443 AM EDT Thu Aug 05 2021 Valid 12Z Thu Aug 05 2021 - 12Z Sat Aug 07 2021 ...Heavy rain and scattered flash flooding possible this morning across southeastern New England, and across parts of northern Florida today... ...Excessive heat across the Desert Southwest; hot and dry conditions with fire weather threat and poor air quality across the interior Northwest... A mid- to upper-level ridge extending northward into the Pacific Northwest will continue to sustain the hot and dry conditions for one more day across the interior western U.S. before a noticeable change in the weather pattern arrives. Although temperatures this afternoon will be not as hot as yesterday, this latest dry spell will once again increase the threat of wildfires especially across the Great Basin. In addition, much of the interior Northwest into the northern High Plains will be enveloped by poor air quality today. Meanwhile, Excessive Heat Warnings remain in effect for the Desert Southwest where another day of high temperatures in the 110s is expected before gradual moderation sets in on Friday. An upper-level low off the coast of California today is forecast to move onshore and head towards the northern Rockies on Friday. This system will signal the beginning of a noticeable change in the general weather pattern across the western U.S., bringing cooler air into the Pacific Northwest during the next couple of days along with a round of rain/thunderstorms pushing across the Intermountain region into the northern Rockies. The rain/storms are expected to continue eastward across the northern Plains on Friday as a complex low pressure system is forecast to develop over the northern High Plains. Heat is expected to build ahead of the complex system across the central High Plains today and especially on Friday where high temperatures are forecast to reach into the upper-90s. Meanwhile, some showers and thunderstorms are expected to move across the Plains today ahead of a lee trough under upper-level support. These rain/storms should gradually weaken as they move toward the Mississippi Valley on Friday. However, the northern extent of the rain across the upper Midwest is forecast to be invigorated by a cold front and a low pressure wave. Some heavier rainfall amounts are possible later on Friday into Saturday as the rain reaches the Great Lakes. Elsewhere, a frontal boundary remains nearly stationary along/near the Gulf Coast as well as just off the East Coast. Some locally heavy rainfall is expected across southeastern New England this morning as a low pressure wave develops along the front and moves across the region. Some heavy rainfall is also possible across northern Florida, as well as across southern Texas into Friday. Fine weather should then return to the Northeast on Friday as the front edges offshore but the trailing portion of the front is forecast to push inland across the Deep South and the Southeast later on Friday. As such, the moderate to heavy rain over northern Florida will then lift northward across the interior Southeast, reaching the Carolinas early on Saturday. Kong Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php