Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 406 PM EDT Thu Jul 15 2021 Valid 00Z Fri Jul 16 2021 - 00Z Sun Jul 18 2021 ...Heavy rain and potential flooding for parts of the Central/Eastern U.S. and the Desert Southwest... ...Heat returns this weekend to the Northern Plains ... A slow moving frontal system across the Northeast, Midwest, and Plains will be the focus for showers and thunderstorms through the period. The airmass south and east of the front is seasonably moist, with dewpoints in the low 70s, contributing to the potential for heavy rainfall and flooding. A Slight Risk for excessive rainfall remains in effect through tomorrow morning for portions of the Central Plains east to the Middle Mississippi Valley, focused on the potential for an additional 1 to 3 inches of rainfall from a cluster of showers and thunderstorms moving eastward just ahead of the front. A Slight Risk for excessive rainfall is in effect from the Middle Mississippi and Lower Ohio Valleys north to the Lower Great Lakes on Friday as widespread rainfall over an inch is expected, with localized maxima of 2-5 inches possible. The flooding threat continues eastward on Saturday with a Slight Risk in effect for portions of the Mid-Atlantic and southern New England, again for the threat of widespread rainfall over an inch with localized totals potentially exceeding 3 inches. Much of this area has also seen significant rainfall over the last couple of weeks, leading to saturated soils and an increased threat for flooding. Heavy rainfall is also expected southwestward along the front across the Ohio and Tennessee Valleys, the Mid-South, and the Southern Plains. Areas further to the southwest will see the threat for heavy rainfall both Friday and Saturday as the front begins to become more stationary with westward extent. Flooding is also a concern in the Southwest as the Monsoon continues. Diurnal heating combined with deep moisture pooled over the area will drive daily afternoon and evening showers and thunderstorms across the Four Corners region. A Slight Risk of excessive rainfall is in effect through Friday morning for portions of eastern Arizona and western New Mexico for the threat of heavy downpours with 1 to 2 inches of rain. This is a particular concern for flooding over burn scars and more urbanized areas. Marginal Risks are also in effect for both Friday and Saturday as the risk for instances of 1-2 inches of rain with any heavy downpours continues. As many high temperatures across the West return closer to normal, albeit still a bit above average in some locations, the concern for hot weather will shift to the Northern Plains as an upper-level ridge builds over the Northern Rockies. High temperatures in the low 100s are forecast for the High Plains of eastern Montana Friday and Saturday, with 90s stretching east across North Dakota and northern Minnesota. An Excessive Heat Watch is in effect for eastern Montana beginning Saturday afternoon. Elsewhere, the Mid-Atlantic and Northeast will remain hot and muggy Friday before the eastward moving front brings some relief, starting with New England on Saturday. Behind the front, the Midwest will see below normal temperatures, with highs in places like Chicago only in the mid-70s. The West Coast will also have cooler temperatures, including much needed relief for Portland and Seattle where highs will be between 70 to 80 degrees. Thunderstorm chances will increase across the High Plains on Friday as the front stalls along the Front Range of the Rockies. Putnam/Campbell Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php