Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 253 PM EST Tue Dec 17 2024 Valid 00Z Wed Dec 18 2024 - 00Z Fri Dec 20 2024 ...Wet and windy weather to continue across the Northwest into tonight... ...Strong to severe storms and heavy rain forecast to develop from the southern Plains to the Tennessee Valley tonight into Wednesday... ...Periods of snow for the Northern Plains through mid-week with heavier accumulations most likely Wednesday night... ...Much above average temperatures expected for most of the Lower 48 into mid-week... The atmospheric river event impacting the Northwest will continue overnight into Wednesday, with precipitation spreading from western Washington and Oregon through the northern Intermountain West and into the northern Rockies. Along the coast, windy conditions with periods of heavy rain are expected tonight. Further inland, apart from the higher elevations of the Cascades and the northern Rockies, snow will likely change to a wintry mix and rain as a strong warm front lifts across the region. Precipitation will wane from the Pacific Northwest to the northern Rockies as an associated upper-level wave moves east of the region by late Wednesday. Precipitation will develop and spread east across the northern Plains into the Upper Midwest as this upper system and an associated area of surface low pressure drops across the region Wednesday night and Thursday. This storm will bring light to moderate snows from North Dakota to Wisconsin, with a wintry mix further south and west, including the threat of accumulating ice from northeastern Montana to eastern South Dakota. Further south and east, a slow-moving frontal boundary extending across portions of the Tennessee Valley back into the southern Plains will become a focus for showers and thunderstorms, with the potential for severe weather and heavy rain. Isolated strong to severe thunderstorms are possible tonight through early Wednesday morning from parts of northeastern Texas to western Tennessee, with the threat continuing across western Tennessee and spreading through Middle Tennessee mid-day. An area of low pressure is expected to organize and track northeast, bringing unsettled weather from the Ohio Valley into the Mid-Atlantic and Northeast late Wednesday. Rain is forecast for most areas from the Ohio Valley to the Mid-Atlantic and the coastal Northeast. Wintry precipitation will be mostly limited to Upstate New York and northern New England, with the more significant threat of accumulating snows confined to the mountains. Further to the south, showers and thunderstorms will develop ahead of the low's trailing cold front as it advances across the Southeast late Wednesday. Apart from the northern Plains and Upper Midwest, temperatures will remain above average across much of the country. Temperatures will be well above average across portions of the southwestern U.S. and may reach record highs from Southern California into the Desert Southwest on Wednesday and Thursday. Pereira Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php