Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 359 PM EDT Sat Jul 10 2021 Valid 00Z Sun Jul 11 2021 - 00Z Tue Jul 13 2021 ...Flooding possible for portions of the central and eastern U.S.... ...Heat wave continues for much of the western U.S. this weekend... ...Strong to severe storms forecast for the Plains... At the start of the short-term forecast period, a cold front extended from the Canadian Maritimes to the southwest just off the Eastern Seaboard with a stationary front extending west through the Carolinas, Ohio Valley, and to a low pressure center currently in place over the Middle Mississippi Valley. A cold front extended to the southwest over the Central and Southern Plains. Widespread showers and thunderstorms are forecast along and ahead of the associated frontal boundaries and the low pressure system moves slowly to the northeast towards the Great Lakes over the next couple of days. High boundary layer moisture is in place across the region, with dewpoints in the low to mid-70s. A Moderate Risk for excessive rainfall is in effect through Sunday morning for portions of the Lower Ohio Valley and Middle Mississippi Valley, with heavy rain rates of 1-2 inches per hour possible with thunderstorms that may train along the stationary front leading to the risk for flash flooding. Multiple Slight Risks for excessive rainfall are also in place for Sunday and Monday along both the cold front that will progress southeast through the Lower Mississippi Valley and east along the stationary front that will begin to lift north as a warm front. The areas with the greatest flash flood risk are along the cold front moving across the Lower Mississippi Valley and into the Southeast where isolated totals of 4-6 inches are possible Sunday and up to 4 inches on Monday as mean southwesterly flow oriented along the cold front may lead to multiple rounds of storms for some locations. There is also an isolated risk for heavy rain amounts up to 5 inches for southern New Hampshire on Monday. In addition to the flash flood risk, severe storms are also possible ahead of the cold front moving southward through the Central and Southern Plains. The Storm Prediction Center has issued an Enhanced Risk for severe thunderstorms today extending from southwest Missouri into northeastern Oklahoma for the threat of large hail and high winds. A Slight Risk is also in effect tomorrow from the Lower Mississippi Valley west through north Texas for the continued risk of high winds with thunderstorms forming along the cold front. The oppressive heat wave continues across the western U.S. as an upper-level ridge remains in place. Potential all-time record heat is forecast in some places, including Las Vegas, where the all-time record high of 117 may be reached today. Widespread high temperatures of 110 and above are forecast for the Southwest deserts as well as the central California valleys. Highs in the 100s are likely across the Great Basin and into the upper 90s for the interior Pacific Northwest. Excessive heat warnings cover most of California and Nevada as well as portions of western Arizona, western Utah, and the Snake River Valley of Idaho. High temperatures into the 100s are also forecast for the High Plains of Montana, where excessive heat watches are in effect. A cold front moving south from Canada will provide relief for Montana on Monday, while a shortwave trough moving east from the Pacific may also provide some relief for portions of northern California. In addition to the heat wave, heavy rain and severe weather are a growing concern for portions of southern Arizona and New Mexico as monsoonal moisture contributes to daily rounds of showers and thunderstorms. Marginal Risks for excessive rainfall are in effect today, tomorrow, and Sunday as the more intense downpours pose the risk of flash flooding with 2" per hour rain rates possible. The Storm Prediction Center has also issued Slight Risks for Severe weather for today and Sunday for the threat of downbursts with high winds. Elsewhere, seasonably mild temperatures are expected through the period across most of the Northeast behind the cold front that has moved into the Atlantic, and also for the Midwest and Central Plains in the wake of the cold front moving south and east across the central U.S. The chance for showers and thunderstorms will continue to pick up across more of the Southwest and Southern Great Basin Monday as monsoonal moisture continues to increase and the upper-level ridge begins to weaken. Showers and thunderstorms are also possible for the Northern Plains along the noted cold front moving south from Canada. Putnam Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php