Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 359 AM EDT Fri May 17 2024 Valid 12Z Fri May 17 2024 - 12Z Sun May 19 2024 ...Potentially significant heavy rainfall threat spreads into portions of southern Mississippi and western Alabama Friday... ...Wet start to the weekend for much of the eastern U.S. as well as the Northern Rockies/Plains... ...Sweltering heat continues across South Florida and southern Texas into this weekend... A broad area of showers and thunderstorms is expected Friday across much of the eastern U.S., with the chance for moderate to heavy rainfall likely to focus from the Lower Great Lakes south through the Appalachians into the Ohio/Tennessee Valleys and to the Gulf Coast. Starting along the Gulf Coast, another day of potentially significant flash flooding is forecast along and to the south of a warm front lifting slowly northward across the region. A Moderate Risk of Excessive Rainfall (level 3/4) has been issued for portions of southern Mississippi and Alabama where a complex of organized, heavy downpour-producing storms is forecast over already saturated soils from storms Thursday night. The location of these additional storms will likely be influenced by the storms ongoing overnight, bringing higher uncertainty and highlighting the importance of remaining aware of the most current forecast. To the north, an active series of shortwaves will help encourage a couple additional areas of locally heavier rainfall focused over portions of the central Appalachians as well as the Lower Ohio/Middle Mississippi Valley. Slight Risks of Excessive Rainfall (level 2/4) are in place for both locations for the threat of some scattered instances of flash flooding. Storm chances will shift southeastward on Saturday, bringing the focus for moderate to heavy rainfall to the southern Mid-Atlantic south along the coastal Carolinas into Georgia and lingering along the central Gulf Coast. A Slight Risk of Excessive Rainfall has been included here for portions of the central Gulf Coast where higher available moisture is most likely to lead to locally heavier downpours on top of already saturated conditions from the previous days' rainfall. Additional scattered instances of flash flooding remain possible. Another frontal system will bring shower and storm chances to the Northern Rockies/High Plains early Friday and the Northern Plains/Upper-Midwest by Friday evening. Generally light to moderate rainfall is expected, with the more moderate rain most likely near the Red River Valley. Cooler conditions may lead to some snow mixing in through the Northern Rockies, though no accumulations are expected. Precipitation chances will taper off into Saturday as the bulk of the system lifts northeastward into Canada. However, to the southwest, some showers and storms will be possible late Saturday into early Sunday along a trailing frontal boundary stretching into the Central Plains. Conditions will continue to remain unseasonably hot and very much Summer-like for portions of South Florida and southern Texas into the weekend. Forecast highs Friday and Saturday range from the low to mid-90s in South Florida and the mid 90s to mid-100s in southern Texas, potentially record-tying/breaking temperatures. High humidity will bring heat indices into the mid- to upper-100s for many locations. Unfortunately, this pattern looks to continue not only into next week but into the following week as well. While not quite as hot, temperatures will also be well-above average and Summer-like across portions of the Northern and Central Plains Friday, with highs in the mid- to upper 80s forecast. These temperatures will shift eastward into the Great Lakes region on Saturday. Variable highs are expected for the rest of the central/eastern U.S., with above average conditions into the 70s for most of the Northeast Friday and Saturday, though portions of the Mid-Atlantic will see a cool down into the 60s Saturday. Slightly below average conditions following a frontal passage over the Southern Plains and Southeast will continue Friday with highs mainly in the 70s to low 80s, though a quick warm-up into the mid-80s to 90s will come Saturday for the Southern Plains. In the West, conditions will be below average in the Pacific Northwest and along coastal California, with highs mainly in the 60s. However, above average conditions are expected into the interior, with highs in the 70s to low 80s in the Great Basin, 80s for the central California valleys, and 90s to low 100s for the Desert Southwest. Putnam Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php