Weather across America

(NATIONAL) A major storm system already bringing heavy mountain snow and coastal rain to the West will begin to shift into the Plains, wintry precipitation for the Interior Northeast with some snow accumulations expected, and episodes of moderate to heavy rainfall possible as showers and thunderstorms continue for the South. 

Heavy mountain snow and coastal rain continued in the West Sunday under the influence of a deepening upper-level trough and strong surge of moisture overspreading the region from the Pacific. Additional snowfall totals generally between 6-12 inches, locally higher, are possible through Monday for the mountains of the Great Basin, Central Rockies, Arizona, and southern California. The heaviest snowfall will continue to be in the Sierra Nevada of California with several feet expected. While most of the significant snow should remain at higher mountain elevations, some light accumulations are possible in the interior valleys, particularly in the northern Great Basin. 

Heavy coastal rainfall intensified by the strong surge of moisture from the Pacific associated with an atmospheric river will shift from the central California coast to southern California on Sunday. There is a Slight Risk of Excessive Rainfall in effect for the Transverse and Peninsular Ranges of southern California where locally high totals of 2-3 + inches may result in scattered instances of flash flooding, particularly in the vicinity of burn scars. In addition to the heavy snow and rain, strong winds will also continue to be a concern. Wind Advisories remain in effect for portions of the central and southern Great Basin and California where gusts running higher than 45 mph remain possible. High temperatures will stay 10-20 degrees below average beneath the upper-level trough.

A strong surface low will begin to develop in the lee of the Rockies early Monday as the upper-level trough continues eastward. Moisture will begin surging northward over the Plains following a developing warm front and ahead of a developing cold front. The anomalously high moisture return ahead of the developing surface fronts as well as the strong system dynamics will help to initiate widespread showers and thunderstorms. 

There is a Marginal Risk of Excessive Rainfall on Monday for portions of southern Kansas, Oklahoma, and north Texas where intense downpours may accompany some of the storms. To the north, Winter Storm Watches are in effect for portions of the Northern and Central Plains as snow will begin to start ramping up late Monday evening. While most of the impacts from this storm are still outside of the current forecast period, the expectation is for widespread heavy snow with the potential for blizzard conditions, and interests should continue to monitor the latest forecasts.

Strong downslope winds ahead of the system will lead to highs 10-20 degrees above average for portions of the High Plains, with 50s and 60s expected more broadly across the Central and Southern Plains. Much colder temperatures in the teens and 20s will begin spreading southward through the Northern Plains Monday.

An upper-level wave moving quickly over the Northeast with an accompanying cold front at the surface will bring the chance for rain and wintry precipitation on Sunday. Snow accumulations of 4-6 inches, locally higher, are forecast for the higher elevations of the Berkshires and Catskills. Lighter accumulations between 1-2 inches will be possible for western New England and interior portions of the northern Mid-Atlantic from New York into central Pennsylvania. While locations in the Mid-Atlantic closer to the coast should see mostly rain, some snow may mix in later Sunday evening. High temperatures are expected to remain a bit cooler than average with highs in the 20s and 30s for New England, 30s and 40s for the Mid-Atlantic, and 50s in the Carolinas.

Small-scale disturbances moving along a frontal boundary slowly drifting southward across the South will continue to help initiate rounds of showers and thunderstorms on Sunday producing areas of moderate to heavy rainfall. There is a Marginal Risk of Excessive Rainfall for portions of the Texas and Louisiana Gulf Coasts into southwestern Mississippi where storms moving roughly parallel to the front may lead to locally heavier rainfall totals and an isolated instance or two of flash flooding. Temperatures north of the front will be a bit cooler than they have been recently with highs in the 60s to low 70s.