Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EST Mon Feb 03 2025 Valid 12Z Mon Feb 03 2025 - 12Z Wed Feb 05 2025 ...Unsettled weather to persist across the Northwest U.S. into early next week with much colder temperatures and heavy snowfall across the Cascades, northern Great Basin, northern Rockies and northern High Plains... ...Strong atmospheric river will continue over the next couple of days across northern and central California with heavy rains and areas of flooding likely... ...Storm system crossing the Great Lakes region to bring accumulating snowfall to parts of the Northeast... ...Record high temperatures are expected across portions of the Southwest out through the Southern Plains through the middle of the week... A persistent trough of low pressure and associated closed low will continue to impact the Pacific Northwest and the northern Rockies going through the first half of the week ahead with widespread unsettled weather expected. Moist onshore flow into the higher terrain coupled with colder temperatures filtering south from southwest Canada will drive heavy accumulating snowfall across the Cascades and especially interior mountain ranges such as the Sawtooth, Bitterroots, Tetons and Absaroka Range. In fact, the strong atmospheric river that is bringing very heavy rainfall to areas of northern California is being steered up the larger scale pattern northeastward up across areas of southern and eastern Oregon, and into the southwest facing slopes of the northern Rockies where there is plenty of cold air in place for very heavy snowfall accumulations and including even some lower elevation locations. For the Cascades, generally an additional 6 to 12 inches of snow is expected through early Wednesday, but considerably heavier amounts are expected for the Shasta/Siskiyou Ranges northeastward into the aforementioned terrain of the northern Rockies where an additional 1 to 3+ feet can be expected. The deep layer fetch of Pacific moisture is also overrunning Arctic air that is well entrenched over the northern High Plains, and this coupled with upslope flow here just east of the Continental Divide will allow for heavy snowfall to accumulate here as well. The strong atmospheric river bringing the heavy flooding rain concerns over northern California should persist through the first part of the week as a stationary front remains anchored in place. Multiple waves of low pressure will traverse this boundary, and this coupled with the Pacific moisture transport and upslope flow/forcing over the higher terrain of the coastal ranges and northern Sierra Nevada foothills should yield as much as an additional 5 to 10 inches of rain. The Weather Prediction Center has depicted a Slight Risk (level 2 of 4) of excessive rainfall across northern California going through early Tuesday. By later Tuesday and Wednesday, the front will be finally settling southward, but this will bring heavy rainfall down into central California including the Bay Area and portions of the Central Valley. Several inches of new rain can be expected here, and a Slight Risk of excessive rainfall has been depicted going into early Wednesday. Farther off to the east, a combination of Pacific moisture arriving from the Western U.S. along with a frontal system traversing the Great Lakes region will bring a swath of accumulating snow for today across areas of Wisconsin and Michigan eastward into northern New York and northern New England. Locally several inches of new snow accumulation is expected. This system will pull away through southeast Canada tonight with a trailing cold front then crossing the region and bringing a new surge of much colder temperatures. Arctic high pressure will be settling south from Canada across much of the northern tier of the nation early this week with temperatures falling locally well below normal. This will especially be the case over the northern High Plains where temperatures will be as much as 15 to 30 degrees below normal, with daytime highs locally staying below zero. However, south of the Arctic front going through the middle of the week, very warm temperatures will be pooled across much of the southern tier of the country. This will include temperatures reaching well into the 80s across the interior of the Southwest and also across the southern Plains. Record high temperatures are expected with some locations seeing high temperatures as much as 20 to 30 degrees above normal. Orrison Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php