Dangerous Flash Flooding likely across Central/Southern California intoearly next week.Heavy Snow will cause extreme impacts over much of the Sierra Nevada onSunday and Monday.Anomalous warmth continues across Northern/Central Plains andUpper/Middle Mississippi Valley.A highly amplified upper-level pattern will support multiple sensibleweather hazards across the CONUS over the next few days. Moderate to heavysnowfall will continue across parts of the Northern/Central Rockiesthrough Sunday before coming to an end Sunday night. Heavy rainfall andscattered thunderstorms will spread into central California tonight as awarm front associated with an approaching low pressure system focusesmoisture and instability over the area. A Slight Risk of ExcessiveRainfall (level 2/4) is in effect for portions of the central Californiacoast from the Bay Area down through Big Sur. Conditions worsen on Sundayas the low pressure system arrives along the California coast. There is aHigh Risk of Excessive Rainfall (level 4/4) over portions of SantaBarbara, Ventura and Los Angeles Counties where the combination of highmoisture, instability and lift (cold front) will produce a dangerous FlashFlooding situation. It's strongly recommended that people: heed warningsfrom emergency management personnel, the local forecast office guidanceand avoid driving through flooded roadways. Broader Moderate (level 3/4)and Slight Risk areas will encompass most of the central and southerncoast as well as upslope areas of the Sierra Nevada and parts of theCentral Valley. This moisture plume will spread east into the Sierra,leading to an extremely impactful heavy snow event over the mountains andactually spilling over into portions of the western Great Basin. WinterStorm Warnings are in effect for the aforementioned areas where 4-6'+ ofsnow is probable. High winds will also be a significant issue withwhipping rain in the low elevations and blowing snow likely in the Sierraon Sunday. The focus for heavy rainfall and scattered thunderstorms shiftinto southern California Sunday night into Monday as the upper lowcontinues to direct energy and moisture into the region beneath apersistently strong jet streak. A Moderate Risk of Excessive Rainfall isin effect for portions of Los Angeles, Orange, San Diego and RiversideCounties where the strong cold front will act as a focus for potentialflash flooding.Elsewhere, a developing low pressure system will focus heavy rain andthunderstorms across the central Gulf Coast tonight. A Slight Risk ofExcessive Rainfall is in effect for portions of southeast Louisiana intosouthern Mississippi. The low pressure system will then move into theeastern Gulf Coast and spread heavy rain and thunderstorm activity intothe Florida Peninsula on Sunday. A Slight Risk of Severe Thunderstorms(level 2/5) is in effect for portions of south Florida where isolated toscattered severe storms will be possible in the morning. An omega blockridge will persist over the central-eastern U.S. through early next week,which will support above average temperatures across the Great Plains,Mississippi Valley and Midwest. The highest anomalies of around +30-40degrees will occur over portions of the Northern Plains and UpperMississippi Valley where high temperatures will be in the 40s while lowtemperatures drop into the upper 20s to mid 30s.