Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 232 AM EST Sat Dec 14 2024 Valid 12Z Sat Dec 14 2024 - 12Z Mon Dec 16 2024 ...Atmospheric River continues to bring very heavy rain with the potential for flooding, heavy mountain snow, and gusty winds to central/northern California Saturday... ...Heavy mountain snow forecast for portions of the Great Basin and northern Rockies Saturday... ...Wintry mix including accumulating freezing rain continues for portions of the Upper Midwest Saturday, spreading into the central Appalachians Sunday... A Pacific storm system and accompanying strong flow of moisture/Atmospheric River continues inland over the West this morning (Saturday) bringing heavy rainfall, mountain snow, and gusty winds to central/northern California and the Pacific Northwest. The heaviest rainfall will continue to focus on portions of central/northern California through Saturday morning where rainfall rates of 0.5" to 1" per hour will lead to an additional few inches of rainfall over already saturated ground. The greatest potential for flooding will be around the greater Bay Area where a Slight Risk of Excessive Rainfall (level 2/4) is in effect. Heavy snowfall will also continue for higher mountain elevations of the Coastal Ranges and Sierra Nevada, generally over 5000 feet, where Winter Storm Warnings have been issued for storm total snowfall of 1-3 feet. Winter Weather Advisories are also in effect further north into the Cascades where storm total snowfall of 8-12", locally 18", can be expected. Gusty winds also continue this morning, particularly along the coast, but all hazardous impacts from the system should begin to taper off through Saturday afternoon. The system will push further inland through the day Saturday, spreading moisture and precipitation chances across the Great Basin and Northern Rockies. A mix of rain and snow can be expected at lower elevations, though any snow accumulations should remain limited. Heavier snow is forecast in the mountains, particularly from central Idaho into western Wyoming, where Winter Storm Warnings are in effect for snowfall of 5-10", locally 12"+. Precipitation chances will spread eastward into the northern High Plains by Saturday night with a wintry mix expected. Some light ice accretions will be possible through the day Sunday. Some gusty winds are also likely along the Front Range of the Rockies as the system pushes out onto the Plains. Further east, an upper-level shortwave/accompanying surface frontal system will help to trigger showers and thunderstorms across the Ohio, Middle Missouri, and Lower Mississippi Valleys Saturday, with some moderate to locally heavy rainfall possible. Storms will likely linger into Sunday along a trailing frontal boundary, though with lighter amounts expected. More impactful weather will continue further north as warmer, moist air overrides colder air at the surface leading to a wintry mix across the Upper Midwest and Great Lakes. Snow/sleet accumulations should remain light, but freezing rain is also expected, particularly over eastern Iowa. An Ice Storm Warning remains in effect through Saturday afternoon for totals potentially exceeding 0.25" and leading to tree and power line damage. The system will continue east on Sunday bringing a wintry mix into the Southern Appalachians. Similar to Saturday, snow/sleet accumulations should generally remain light, but some ice accretions over 0.1" will be possible. Elsewhere, some showers and thunderstorms can be expected this weekend along the Atlantic Coast of the Southeast and Florida with a quasi-stationary frontal boundary in place. Additionally, after a brief break late Saturday/early Sunday, another system over the Pacific will bring increasing precipitation chances back to the Pacific Northwest by Sunday evening. Most of the country will see high temperatures at or above average this weekend as conditions moderate following a cold frontal passage across the South and with an upper-level ridge passing over the central/western U.S. ahead of the next Pacific system. Some of the warmest temperatures will be in the Southern Plains/Texas with highs in the 60s, 70s, and even some low 80s. Otherwise, temperatures generally range from the 30s and 40s from the Pacific Northwest and Great Basin east through the northern Plains, Great Lakes, and Northeast; the 50s and 60s for California, the central Plains, Ohio Valley, and the South; and 70s for the Desert Southwest and Florida. Putnam Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php