Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EST Sat Feb 01 2025 Valid 12Z Sat Feb 01 2025 - 12Z Mon Feb 03 2025 ...Unsettled weather to bring lower elevation rains and heavy mountain snowfall across the Pacific Northwest and the northern Rockies going through the weekend... ...Strong atmospheric river to bring heavy rains and flooding concerns to areas of central and northern California... ...New storm system ejecting out across the northern Plains will bring accumulating snowfall to portions of the Upper Midwest, Great Lakes and Northeast... A switch to a very unsettled weather pattern is underway across the Northwest and much of the West Coast as a more zonal flow pattern unfolds. This will bring moist onshore Pacific flow with lower elevation rains and increasingly heavy mountain snowfall for the Cascades and also the northern Rockies. Going through Sunday, as much as 1 to 3 feet of new snowfall is expected over the high terrain, and snow levels will actually be falling with time as colder air also settles south from southwest Canada. This allow temperatures to drop below normal with high temperatures as much as 5 to 10+ degrees below average by the end of the weekend. As unsettled weather impacts the Northwest, strong deep layer Pacific flow along with a quasi-stationary front will become situated over central and northern California and this will set the stage for a persistent and strong atmospheric river to impact the region. Heavy to excessive rainfall is expected for the coastal ranges, including areas around the Bay Area, and especially areas farther inland into the foothills and higher terrain of the northern Sierra Nevada. Multi-day rainfall totals through Sunday for the coastal ranges may reach see as much as 3 to 6 inches. However, for the upslope areas of the Sierra Nevada, as much as 6 to 12 inches of rain is forecast, and with high snow levels, there will be strong concerns for flooding. This will include a threat for burn scar flash flooding/debris flow activity locally. Heavy rains will be impacting the Sacramento Valley and some flooding will be possible here as well. The Weather Prediction Center has depicted a Slight Risk of excessive rainfall across the region (level 2 of 4) to address the multi-day flooding concerns associated with this impending atmospheric river activity. Meanwhile, a new storm system related to the unsettled weather unfolding across the West will begin to eject east out across the northern Plains later Saturday through Saturday night this will bring a threat for several inches of accumulating snow to the Upper Midwest. This system will then begin to lift up into southeast Canada going through Sunday, but will bring a threat for snowfall also across portions of the Great Lakes region and the Northeast where there will be sufficient cold air in place. In the wake of this system, much colder air will be settling southward across the northern Plains which will allow temperatures to begin returning back to below normal. Elsewhere, very mild temperatures with above average highs can be expected across much of the rest of the Plains region and the South. In some cases across the Plains and Midwest, the temperatures this weekend will be as much as 15 to 20 degrees above normal. Many areas of the Southeast and the Southwest will also be warmer than normal with highs as much as average 5 to 10+ degrees above average. Orrison Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php