Life threatening and damaging Flash Flooding likely across much ofcentral/southern California through Monday.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 andsouthern California over the next few days. High rain rates over veryvulnerable/primed surfaces will lead to flash flooding tonight acrossportions of central and southern California, which is why there's aModerate Risk of Excessive Rainfall (level 3/4) for this area with anembedded High Risk (level 4/4) area over parts of Santa Barbara, Venturaand Los Angeles Counties. Heavy rain will also occur over the foothills ofthe Sierra Nevada tonight where a Slight Risk of Excessive Rainfall (level2/4) is in effect. Heavy snow will continue across the Sierra and ShastaSiskiyous through Monday where 1-3' of snow are expected with isolated 4'amounts over the highest elevations. Some snow is also likely for theGreat Basin where up to a foot of snow is possible over portions ofcentral Nevada. Strong winds will cause high surf up and down theCalifornia coast, whipping rain at lower elevations and blowing snowacross the Sierra are also likely with High Wind and Winter Storm Warningsin effect for parts of the state.The moisture plume sags south Monday night into Tuesday and focuses alonga surface cold front over southern California and the southern SierraNevada. Heavy to Excessive Rainfall is likely from San Luis County down toSan Diego County, where a Slight Risk of Excessive Rainfall is in effect.Another High Risk of Excessive Rainfall is in effect for parts of LosAngeles and Orange Counties on Monday where areal totals of 1-3" of rainand isolated higher amounts are possible. Heavy Snow impacts will waneacross northern/central Sierra while continuing over the southern sectionof the mountain range. Cool air will filter in on the backside of the coldfront and allow for heavy snow to develop over the higher elevations ofthe Transverse Ranges. About another foot of snow is forecast for thesouthern Sierra, and 1-2' are possible over the Transverse Ranges andCentral Great Basin. Rain and snow will continue over the Central GreatBasin of Nevada where around a foot of snow is expected.Elsewhere, some moderate to heavy rain and thunderstorms are possible overcoastal areas of Georgia and South Carolina tonight where a Marginal Riskof Excessive Rainfall is in effect (level 1/4). Around an inch of rainfallis currently forecast for that area. Some light rain and snow are alsopossible over portions of the Pacific Northwest and Northern Rockies. Upto a foot of snow is possible for parts of the Cascades and NorthernRockies through Monday afternoon. An upper-level ridge will strengthenover the Central U.S. this week, leading to increasingly abnormally mildtemperatures for much of the Central and Eastern thirds of the country.Temperatures across the Northern Plains and Upper Midwest will be 30-40degrees above average which may tie or break existing daily temperaturerecords.