Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 356 PM EDT Fri Jul 02 2021 Valid 00Z Sat Jul 03 2021 - 00Z Mon Jul 05 2021 ...Excessive heat continues across sections of the Northwest, extending into the Northern Rockies, the Northern Plains and the Upper Midwest... ...Isolated heavy rainfall likely along a cold front from the Mid-Atlantic through the Deep South and into the Southern High Plains... ...Monsoonal moisture will bring daytime showers and thunderstorms with locally heavy rainfall to the Southwest through the weekend... Anomalous ridging continues to dominate the upper-level pattern over the western United States, prolonging the excessive heat exposure for residents of the interior Northwest to the Northern Plains throughout the holiday weekend. Daily high temperatures in these regions will remain 15 to 20 degrees above normal, with some places consistently reaching the upper 90s or low 100s. A handful of daily records could potentially be broken from the Northern Great Basin to the Upper Midwest on Saturday. Due to the ongoing exposure to oppressively high daytime temperatures in parts of the Columbia Basin and the dangerous heat forecast to affect parts of Montana on Saturday and the Dakotas on Sunday, residents of these areas are urged to take proper precautions to safeguard their health and prevent the onset of heat-related illness. These precautions include: avoiding long periods of time outdoors in the sun, staying hydrated, remaining in a cool or air conditioned location, and canceling outdoor activities during the heat of the day. Excessive Heat Watches and Warnings as well as Heat Advisories are currently in effect for portions of Washington, Oregon, Idaho, and Montana. Showers and thunderstorms are likely along a long, southward moving frontal boundary extending from the Mid-Atlantic through the Deep South and into the Southern High Plains. Due to the slow progression of and the potential for heavy convective precipitation with the passage of the front, localized flash flooding will be a concern along the length of the boundary. One of the areas at greatest risk for flash flooding through Saturday morning is the Mid-Atlantic. The Weather Prediction Center has highlighted a Slight Risk for Excessive Rainfall along the southern Virginia and Carolina coastlines, where antecedent conditions could support high rainfall rates on the order of 1 to 2 inches per hour. Heavy rainfall and flash flooding threats are expected to continue throughout the South this weekend as the front stalls along the Gulf Coast. With the passage of the front, daily high temperatures from the Northeast to the the Central High Plains are forecast to drop 10 to 20 degrees below normal on Friday and Saturday. Upper-level high pressure settling over the Four Corners region will assist in pulling monsoonal moisture into the Southwest, bringing diurnally driven showers and thunderstorms from Arizona into the southern Rockies/High Plains throughout the period. Moderate to isolated heavy rainfall is possible, with concerns for flash flooding expected to persist through much the weekend across portions of southern Arizona, New Mexico, and western Texas. The Weather Prediction Center has highlighted Marginal to Slight Risks for Excessive Rainfall in these regions. To the north, daytime showers and thunderstorms will be likely across parts of the Central/Northern Plains along a weak stationary/warm frontal boundary. Zavadoff Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php