Weather across America

(NATIONAL) Life threatening and damaging Flash Flooding likely across much of central/southern California through, heavy snow for parts of the Sierra Nevada and the Great Basin, the ongoing Atmospheric River event will continue to produce heavy rain, strong winds, high surf, and heavy snow across much of central and southern California.

High rain rates over very vulnerable/primed surfaces will lead to flash flooding Sunday night across portions of central and southern California, which is why there's a moderate risk of excessive rainfall (level 3/4) for this area with an embedded high risk (level 4/4) area over parts of Santa Barbara, Ventura and Los Angeles Counties. Heavy rain will also occur over the foothills of the Sierra Nevada Sunday night where a slight risk of excessive rainfall (level 2/4) is in effect. 

Heavy snow will continue across the Sierra and Shasta Siskiyous through Monday where 1-3' of snow are expected with isolated 4' amounts over the highest elevations. Some snow is also likely for the Great Basin where up to a foot of snow is possible over portions of central Nevada. Strong winds will cause high surf up and down the California coast, whipping rain at lower elevations and blowing snow across the Sierra are also likely with high wind and winter storm warnings in effect for parts of the state.  

The moisture plume sags south Monday night into Tuesday and focuses along a surface cold front over southern California and the southern Sierra Nevada. Heavy to excessive rainfall is likely from San Luis County down to San Diego County, where a slight risk of excessive rainfall is in effect. Another high risk of excessive rainfall is in effect for parts of Los Angeles and Orange Counties on Monday where areal totals of 1-3" of rain and isolated higher amounts are possible. Heavy snow impacts will wane across northern/central Sierra while continuing over the southern section of the mountain range. 

Cool air will filter in on the backside of the cold front and allow for heavy snow to develop over the higher elevations of the Transverse Ranges. About another foot of snow is forecast for the southern Sierra, and 1-2' are possible over the Transverse Ranges and Central Great Basin. Rain and snow will continue over the Central Great Basin of Nevada where around a foot of snow is expected.  Elsewhere, some moderate to heavy rain and thunderstorms are possible over coastal areas of Georgia and South Carolina Sunday night where a marginal risk of excessive rainfall is in effect (level 1/4). 

Around an inch of rainfall is currently forecast for that area. Some light rain and snow are also possible over portions of the Pacific Northwest and northern Rockies. Up to a foot of snow is possible for parts of the Cascades and northern Rockies through Monday afternoon. An upper-level ridge will strengthen over the central U.S. this week, leading to increasingly abnormally mild temperatures for much of the central and eastern thirds of the country. Temperatures across the northern Plains and upper Midwest will be 30-40 degrees above average which may tie or break existing daily temperature records.