Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 343 AM EDT Sun Jul 28 2024 Valid 12Z Sun Jul 28 2024 - 12Z Tue Jul 30 2024 ...Flash flooding possible in the Ohio/Tennessee Valleys Sunday, spreading into the central/southern Appalachians by Monday... ...Severe thunderstorms expected across portions of the Northern/Central Plains with flash flooding into the Upper Midwest Sunday... ...Cooler than normal for much of the West with monsoonal thunderstorms for portions of the Southwest... A lingering frontal boundary snaking through the Ohio/Tennessee Valleys deeper into the Southeast and off the Atlantic coast will continue to help trigger scattered showers and thunderstorms over the next couple of days. An upper-level wave passing over the Ohio/Tennessee Valleys will provide a focus for more numerous storms on Sunday, possibly into the central/southern Appalachians as well, with very moist, southerly Gulf flow leading to some locally heavy downpours. A Slight Risk of Excessive Rainfall (level 2/4) is in effect for the threat of some scattered instances of flash flooding, particularly where storms may have the tendency to backbuild/repeat over areas in vicinity of the frontal boundary. Then, as the upper-level wave continues east on Monday, the focus for storms will spread further into the central/southern Appalachians, with another Slight Risk of Excessive Rainfall in effect for additional instances of flash flooding. High temperatures broadly across the Ohio Valley into the Southeast and along the Gulf Coast will remain at or a bit below average given widespread clouds and storms, with highs generally in the mid-80s to low 90s. A frontal system passing slowly through the Northern/Central Plains and the Upper Midwest will bring storm chances to these regions Sunday. Plentiful moisture, instability, and strong upper-level flow overhead leading to sufficient deep-layer shear is expected to result in some more intense, organized storms. Initially isolated storms/supercells over portions of South Dakota, central Nebraska, and northwestern Kansas may produce some large hail and damaging winds. Eventual upscale growth into an organized convective system Sunday evening may bring a damaging wind threat downstream into southwestern Minnesota and northwestern Iowa. The Storm Prediction Center has highlighted these areas with a Slight Risk (level 2/5) of severe weather. The expanding coverage of storms heading eastward, as well as plentiful moisture to lead to heavy rainfall rates, will also bring the threat of flash flooding into Iowa. Additional storms will continue ahead of the front over Minnesota through early morning Sunday, with another round of storms expected Sunday night. Repeated storms bringing heavy rainfall on top of already wet antecedent conditions will lead to the risk of some scattered flash flooding here as well. A Slight Risk of Excessive Rainfall extends from portions of Minnesota southward into Iowa to cover these threats. The system will continue into the Great Lakes region Monday, bringing showers and storms with moderate to locally heavy rainfall. High temperatures ahead of the front will be rather hot, running 10-15 degrees above average for some locations, with 80s to near 90 in the Upper Midwest and 90s to low 100s southwestward into the Central Plains and southern High Plains. A few near record-tying/breaking highs will be possible in the southern High Plains Monday. An upper-trough over the West will keep temperatures below average for most of the region. Forecast highs Sunday-Monday range between the 60s and 70s along the Pacific Coast; 70s and 80s in the Pacific Northwest; 80s and 90s in the Great Basin, Four Corners Region, and interior California; and the 100s into the Desert Southwest. Some Monsoonal storms will continue over parts of the Southwest, particularly southeastern Arizona/southwestern New Mexico, with an isolated threat of flash flooding. A storm system approaching the Pacific Northwest will bring some shower chances here as well. Smoke from wildfires will also continue to plague parts of the West, particularly over the northern Great Basin/Rockies, resulting in poor air quality and areas of reduced visibility. Elsewhere, conditions will be trending hotter across most of the Northeast, with 80s and low 90s forecast. A coastal low approaching southern New England is looking more likely to bring cooler temperatures and some rain chances over the next couple of days. Putnam Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php