Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 406 PM EDT Fri Jul 16 2021 Valid 00Z Sat Jul 17 2021 - 00Z Mon Jul 19 2021 ...Showers, thunderstorms, and the potential for flooding across the central and eastern U.S.... ...Additional rounds of heavy rain and thunderstorms for the Southwest... ...Excessive heat builds into the Northern Plains and Intermountain West this weekend... A slow moving frontal system will progress east across the central and eastern U.S. through the short-term forecast period. Showers and thunderstorms are expected to continue along and ahead of the front in the presence of a seasonably moist airmass. Widespread rainfall of 1-2 inches is likely over the weekend from the Northeast and Mid-Atlantic southwestward through the Southern Plain. A Slight Risk for Excessive Rainfall remains in effect through tomorrow morning for portions of the Lower Great Lakes and Ohio Valley where locally higher amounts of 3-5 inches of rain are possible. The greatest risk for flooding will be further east on Saturday where a Moderate Risk is now in effect for southern New England, southern New York, northeastern Pennsylvania, and northern New Jersey. A broader Slight Risk is in place for the northern Mid-Atlantic, New York, and southern New England. Locally heavy rainfall amounts of 2-3 inches and higher are possible. Attention is focused on the Moderate Risk area due to the consistent heavy rainfall seen over the region recently leading to already saturated soils. Some areas have seen rainfall between 300 to 500% above normal in the last week. Heavy rainfall and the potential for flooding will be a concern elsewhere further south and west along the front from the Carolinas west through the Southern Appalachians, Tennessee Valley, Mid-South, and Southern Plains. Broad Marginal Risks for excessive rainfall are in effect for these areas on both Saturday and Sunday. In the Southwest, daily showers and thunderstorms sparked by the continued influx of Monsoonal moisture will lead to the potential for flooding. Marginal Risks for excessive rainfall are in effect for both Saturday and Sunday across portions of the Desert Southwest and Southern Rockies. Heavy downpours look to remain somewhat isolated, but slow moving storms with instances of 1-2 inches of rain may pose a risk for flash flooding, especially over any burn scars or in more urban areas. Besides the heavy rainfall, a heatwave across the Northern Tier of the country will become an increasing concern into the weekend as a ridge builds in over the West. High temperatures will begin to peak first and foremost in eastern Montana, where an Excessive Heat Warning will take effect Saturday afternoon. Highs in the low 100s Saturday may approach the mid 100s on Sunday. The heat will continue to expand on Sunday to include the northern Intermountain West, Plains, and Midwest. Highs in the low 100s are forecast for Idaho, northern Utah, and northern Nevada, with highs in the mid to upper 90s expected elsewhere across the region. An Excessive Heat Watch is in effect for the eastern Snake River Valley in Idaho. Elsewhere, thunderstorm chances will increase on Saturday and Sunday across the Central and High Plains as the western end of the front remains stationary to the east of the Front Range of the Rockies and a shortwave moves southward across the region. Some instances of heavy rain with rates of up to 1.5 inches per hour are possible on Sunday, and a Marginal Risk is in effect for portions of the Central Plains. The cold front moving across the East and associated showers and storms will bring a cool down to the Mid-Atlantic and Northeast, with high temperatures dropping into the 70s for New England and the 80s further South by Sunday. Below normal temperatures for mid-July are also expected behind the front across most of the eastern U.S. and Plains. Putnam Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php