Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 420 AM EDT Tue Mar 21 2023 Valid 12Z Tue Mar 21 2023 - 12Z Thu Mar 23 2023 ...Powerful storm system to spread high winds, heavy rain, and heavy mountain snow to parts of California and the Southwest... ...Widespread rain/heavy mountain snow expected to move across the Great Basin and the central/southern Rockies through Thursday morning... ...A couple quick rounds of light-to-moderate snowfall are expected across portions of the northern Plains and Upper Midwest through Thursday morning... A low pressure system currently developing rapidly over the Pacific to the west of California is forecast to deliver quite an impactful weather event through the southwestern quadrant of the country over the next couple of days. The outer edge of the precipitation associated with this system is already moving onshore across southern California. Heavy rain and heavy mountain snow will likely expand through California, the Great Basin followed by the Four Corners and through the central and southern Rockies as the system slams onshore and moves across these areas through Thursday morning. In addition, potentially damaging wind gusts can accompany the system, especially when the storm center is forecast to approach and/or make landfall near San Francisco this evening, as the system possibly acquires some sub-tropical characteristics near the center under an anomalously cold upper low over the ocean. Farther south, a strong pressure gradient could lead to maximum wind gusts near 75 mph across southern California. Meanwhile, a surge of subtropical moisture will accompany this system and create a ripe environment for heavy rain from the central coastline to southern California. Heavy rain is likely to lead to rapid runoff and areas of flooding across southern California, with isolated flooding instances possible for regions to the north. For the mountainous terrain of the southern/central Sierra Nevada and Southern California, heavy snow will be the primary hazard as snowfall accumulations add up to as much as 3 to 4 feet in spots. This additional snowfall will lead to difficult travel and could strain infrastructure in areas still buried under a record-breaking snowpack for the year-to-date. Impacts are also anticipated to spread farther inland during the second half of Tuesday across the Southwest, central Great Basin, and south/central Rockies. Gusty southwesterly winds up to 60 mph are possible across the Desert Southwest, with heavy rain and localized flash flooding possible across parts of central Arizona. Elevated terrain from central Nevada to western Colorado can expect heavy snow to last into Wednesday. Dangerous to difficult travel is likely, with most mountain ranges experiencing over a foot of snowfall. Numerous wind, flood, and winter headlines have been issued for the upcoming storm. Be sure to check with your local forecast office for details. Wintry weather will also impact the north-central U.S. through early Thursday as two separate systems traverse the region. Between Tuesday and Wednesday morning, a low pressure system is forecast to swing from the northern Plains to the Upper Great Lakes, with locally heavy snow possible just to the north from southeast North Dakota to northern Minnesota. Snowfall amounts up to 7 inches are possible and when combined with areas of blowing snow, visibility could be reduced and create treacherous driving conditions. Beginning late Wednesday, the western U.S. system is forecast to redevelop over the central U.S. where a swath of additional snowfall from south Dakota to southern Minnesota is expected just to the south of the first storm. Snowfall totals could add up to over 4 inches. Farther south and east, scattered showers and thunderstorms are anticipated to develop along a stationary front Wednesday night across portions of the Midwest. Elsewhere, one more chilly morning is expected for the Southeast today before springlike temperatures migrate eastward from the southern Plains by midweek. Low temperatures tonight are still likely to dip below freezing throughout the Tennessee Valley and Southeast. Freeze Warnings and Frost Advisories have been issued from eastern Mississippi to the Carolinas in order to highlight the potential for damage to sensitive vegetation and unprotected outdoor plumbing. Meanwhile, rain is forecast to expand eastward across the Ohio Valley and Great Lakes on Wednesday before reaching New England early Thursday with some wintry precipitation expected for northern New England. Kong/Snell Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php