Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 234 AM EST Wed Nov 13 2024 Valid 12Z Wed Nov 13 2024 - 12Z Fri Nov 15 2024 ...Atmospheric River brings heavy coastal rain and high-elevation mountain snow to the Pacific Northwest and northern California Wednesday... ...Showers and thunderstorms will bring locally heavy rainfall to the Lower Ohio, Tennessee, and Mississippi Valleys Wednesday, with the risk for some scattered flash flooding in Louisiana and Mississippi... ...Above average temperatures continue for much of the central U.S. and Gulf Coast states while colder air moves into the Northeast and the West... Heavy lower elevation rain and high elevation mountain snow continues in the Pacific Northwest this morning as a Pacific frontal system and associated plume of moisture/Atmospheric River move inland over the region. Precipitation coverage will expand southward into northern California through the day Wednesday, with favorable upslope locations along the coastal ranges and Cascades seeing locally heavy rainfall with an isolated risk for flooding. Precipitation will also spread inland with the front into the northern Rockies/Great Basin bringing rain and a wintry mix to lower elevations and more snow to higher elevations in the local mountain ranges. Precipiation chances across the region will continue into Thursday, though with more moderate amounts expected as the moisture flowing in from the Pacific wanes. Gulf moisture flowing northward ahead of a low pressure/frontal system over the Mississippi Valley will help trigger a broad area of showers and thunderstorms today stretching from the Midwest/Great Lakes south through the Ohio, Tennessee, and Lower Mississippi Valleys. Greater and deeper moisture content closer to the Gulf as well as some marginal instability will bring the threat for some locally heavy downpours producing a few inches of rain for the Lower Ohio, Tennessee, and Lower Mississippi Valleys, where a Marginal Risk of Excessive Rainfall (level 1/4) is in effect for some isolated flash flooding. A targeted Slight Risk (level 2/4) has been introduced from central Louisiana northeast into central Mississippi where higher confidence in greater rainfall rates and very wet antecedent conditions from prior heavy rainfall events may lead to a few more scattered instances of flash flooding. The system will continue eastward on Thursday, bringing shower and thunderstorm chances to the Upper Ohio Valley, Appalachians, and the Carolinas/Southeast, while lingering across the Great Lakes. Some more moderate to locally heavy rainfall totals are most likely across the central/southern Appalachians and Carolinas where precipitation will be enhanced by a second frontal boundary lifting northward from the Gulf. The rest of the country will remain mostly dry. Much of the central U.S. and Gulf Coast states continue to see above average high temperatures by around 5-15 degrees this week. Forecast highs Wednesday and Thursday range from the 40s and 50s in the Great Lakes/Midwest; 50s in the northern Plains; 50s and 60s in the central Plains, Middle Mississippi Valley, and Ohio Valley; the 70s for Texas and the Lower Mississippi Valley, and the 80s along the Gulf Coast and into Florida. Frontal passages and generally unsettled weather along the East Coast and in the West will keep temperatures cooler and more seasonable in these areas. Forecast highs range from the 30s and 40s in New England, the 40s and 50s in the Mid-Atlantic, and the 50s and 60s from the Carolinas south into Georgia. In the West, highs Wednesday are in the 40s and 50s for the Pacific Northwest and Interior West, the 60s in California, and the 70s in the Desert Southwest. Temperatures will moderate for eastern interior areas on Thursday as upper-level ridging builds northward, with highs climbing into the 50s and 60s for the Rockies and Four Corners Region, and the 80s for the Desert Southwest. Putnam Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php thunderstorms and isolated flash flooding concerns to the Tennessee and Mississippi as well as the lower Ohio Valleys Wednesday