Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 PM EDT Fri Sep 27 2024 Valid 00Z Sat Sep 28 2024 - 00Z Mon Sep 30 2024 ...Life-threatening, catastrophic flash and urban flooding ongoing in the Southern Appalachians due to rainfall from Helene... ...Risk of heavy rainfall leading to scattered instances of flash flooding as well as high winds continues through tonight for portions of the Southeast and Ohio/Tennessee Valleys... ...Heavy rainfall and isolated flash flooding due to Post Tropical Storm Helene for portions of the Ohio/Tennessee Valleys Saturday... ...Well above average temperatures and summer-like heat expected from the Southwest to the Northern Plains this weekend with numerous record tying/breaking highs possible... Now post-tropical storm Helene continues to move through the Southeast and into the Tennessee/Ohio Valleys this afternoon with a broad swath of rain stretching from the Mid-South east through the Ohio/Tennessee Valleys and into the central Appalachians as well as southern Mid-Atlantic/Carolinas. While rainfall has trended down overall, or has completely ended for some locations over portions of the southern Appalachians, life-threatening, catastrophic flash and urban flooding continues. There have been numerous high-water rescues, roads closed, and at least one dam failure. The threat for flooding will also continue as river levels remain at high to potentially record-breaking levels. Additional locally heavy rainfall on top of already very wet antecedent conditions elsewhere across the region will continue into the evening, bringing the threat for additional scattered instances of flash flooding. A broad Slight Risk (level 2/4) of Excessive Rainfall remains in place. Strong, potentially damaging wind gusts will also continue into the evening/early overnight hours as well. There is a possibility of long-duration power outages in portions of the Southeast following the storm. Remember, if you use a generator, be sure it is placed outside at least 20 feet away from doors, windows, and garages to avoid deadly carbon monoxide poisoning. The Storm Prediction Center has also outlined portions of southeastern Virginia and North Carolina with Slight (level 2/5) to Enhanced (level 3/5) risks of severe weather mainly for the threat of tornadoes. Post-tropical storm Helene and an upper-low that has been lingering over the Mississippi Valley will begin to interact and bring additional locally heavy rainfall to portions of the Ohio Valley and Tennessee Valleys on Saturday, with some isolated flash flooding remaining possible. The rainfall will begin to reduce in coverage and shift eastward on Sunday as the upper-low meanders eastward, with some isolated flash flooding possible in the central Appalachians. A locally higher threat could materialize if storm coverage/duration overlaps areas of wetter antecedent conditions from the prior days rainfall due to the storm, with additional Slight Risks not out of the question. Additional moderate rainfall is expected ahead of a lingering quasi-stationary frontal boundary through the Mid-Atlantic this weekend, though amounts here should remain lighter. Showers and thunderstorms with locally heavy rainfall are also expected ahead of a stalling cold front over the Florida Peninsula, with some isolated flash flooding possible. The rest of the country will be mostly dry through the weekend. Much above average, summer-like high temperatures continue under the influence of a broad upper-level ridge over the western/central U.S., particularly for the Desert Southwest, Great Basin, and northern Plains. Extreme Heat Warnings remain in place in the Desert Southwest as highs soar into the 110s. Forecast highs are in the mid-80s to mid-90s over much of the northern Plains and Great Basin, in some cases upwards of 20-30 degrees above average. Numerous potentially record-tying/breaking highs are possible. An Pacific system moving into the Northwest will bring temperatures down to average for the northern Great Basin Sunday. While not quite as warm, conditions will also be above average for the Upper-Midwest as highs reach into the upper 70s to mid-80s. Elsewhere, hot, humid conditions will continue ahead of a cold front in South Florida. Putnam Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php