Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 PM EDT Fri Aug 16 2024 Valid 00Z Sat Aug 17 2024 - 00Z Mon Aug 19 2024 ...A Slight Risk of excessive rainfall tonight over the southern Appalachians and interior Southeast through tonight, shifting into the northern Mid-Atlantic on Sunday... ...A Slight Risk of severe thunderstorms over parts of the Central/Southern Plains tonight, over the interior Pacific Northwest and upper Ohio Valley on Saturday, and across the Southeast and Carolinas on Sunday... ...Excessive Heat Warnings and Heat Advisories are in effect across the central/southern Plains into the lower Mississippi/Tennessee Valleys... The prevailing weather pattern across mainland U.S. will continue to favor precipitation and cooler than normal temperatures across the northeastern quadrant of the country while heat will continue in portions of the interior western U.S. and especially over the southern Plains. A low pressure system currently centered over the upper Midwest is forecast to progress slowly but steadily through the Great Lakes for the next couple of days. This system will be responsible for bringing considerable clouds along with widespread modest rainfall with embedded thunderstorms across the Great Lakes reaching into New England by Sunday. The chance of heavy rainfall will be greater farther to the south in the warm sector across the southern Appalachians into the interior Southeast through tonight as clusters of thunderstorms develop ahead of the trailing cold front. Some of these thunderstorms could become severe across the upper Ohio Valley on Saturday. By Sunday, the front will progress into the East Coast states with heavy rain possible over the northern Mid-Atlantic where a low pressure wave is forecast to form. Farther south ahead of the cold front, thunderstorms could become severe across the Southeast and into the Carolinas on Sunday. Over the western U.S., monsoonal moisture combining with daytime heating will trigger showers and thunderstorms over parts of the Southwest, eastern Great Basin, and into the southern Rockies from late afternoon into late evening during the weekend. An upper-level trough moving onshore over the Pacific Northwest is forecast to trigger thunderstorms which could turn severe over the interior sections on Saturday. Meanwhile, upper-level ridging over parts of the southern Plains and lower Mississippi Valley will support high temperatures in the upper-90s to low-100s with dew points in the low to mid-70s across the region. This level of heat and humidity has prompted Excessive Heat Warnings and Heat Advisories over parts of the central/southern Plains and across the lower Mississippi into the Tennessee Valleys. This prolonged stretch of high temperatures in the upper 90s and triple digits will persist through the weekend. Low temperatures around 80 degrees are also forecast along the Gulf Coast with daily maximum heat indices nearing 110F farther inland up the lower Mississippi Valley. Please practice heat safety if you need to spend time outdoors or in a building without air conditioning. Kong/Ziegenfelder Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php