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| Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 1227 AM EST Sun Dec 22 2024 Valid 12Z Sun Dec 22 2024 - 12Z Tue Dec 24 2024 ...Periods of moderate to heavy rainfall for the Pacific Northwest and northern California as systems move in from the North Pacific... ...Record warmth possible across parts of the Southwest on Sunday... ...More winter weather from the northern Plains through the Great Lakes and the Northeast from Sunday into Tuesday morning... The general flow pattern becomes more zonal with time, with systems of Pacific origin moving eastward and reforming downstream across the Plains/Midwest. The consequence of this pattern will be rainfall/elevation snows near the Pacific Northwest & northern California, decreasing warmth across the West, and by Monday decreasing cold across portions of the East. Starting out West, weakening fronts move eastward out of the Pacific into the Great Basin, pushing batches of rainfall into and through the Pacific Northwest, northern Intermountain West, and northern California, with snowfall expected at higher elevations through Tuesday morning. The heaviest precipitation is expected in and near northern California Monday night and Tuesday, which carries some risk of excessive rainfall/flash flooding, particularly in burn scars. Some periods of high winds are expected on Sunday -- wind advisories are in effect for areas of northern California and southern Oregon. Across the Southwest, high temperatures should rise 60s to 70s on Sunday, threatening daily record high temperatures in and near southern Arizona and southern California. As one of the Pacific disturbances aloft moves east of the Rockies, a low pressure system develops across the Upper Midwest and Great Lakes Sunday into early Monday, which is expected to bring freezing rain to portions of northeast Montana and northwest North Dakota -- winter weather advisories are in effect -- then snowfall which increases in coverage and intensity with time from North Dakota eastward through Michigan into the Northeast. This system should weaken as it moves through the Northeast. A seasonably strong and cold high pressure system migrates through the East into the Western Atlantic on Sunday and Monday, continuing the cold in the eastern United States. Cold Weather Advisories are in effect across portions of eastern Upstate New York and northeast Pennsylvania, while freeze warnings and frost advisories are out for portions of southeast Georgia and North Florida for Sunday morning. As the flow over the Great Lakes becomes more anticyclonic with time, Lake Effect Snows should continue to fade on Sunday. For some areas of the East, Sunday should be the coldest day thus far this winter. Once the high moves offshore on Monday, temperatures should begin to moderate closer to late December averages. Roth |
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