Weather across America

(NATIONAL) Heavy rain threat emerges across the South, periods of mixed rain and snow linger across Interior New England, unsettled and windy weather spreading across the North, above average temperatures will overspread the central and eastern U.S. and cold air surging into the West.

Strong Santa Ana Winds result in Critical Fire weather day starting Monday across Southern California. The last vestiges of cold air are being dispelled out of New England for the remainder of Sunday into Sunday night with some lingering snow showers still possible across far Interior New England. Clearing skies and return flow ahead of the Pacific System sliding through the Rockies, combining with warmer/moist air returning out of the Western Gulf ahead of an average upper-level trough; will result in well above temperatures today across the Northern Plains and Midwest, shifting to the eastern half of the country on Monday, and finally east of the Mississippi into Tuesday ahead of the Pacific cold front.  

Sunday, 20 to 30 degree departures will exist in the Plains and temper a bit to 15 to 25 degrees above normal overnight Sunday through Tuesday morning. Increased moisture through the lower Mississippi River Valley will have some stronger showers and possible thunderstorms closer to the Gulf of Mexico.  Rain rates may result in a few widely scattered incidents of flooding across the Delta Region into SW LA Sunday, shunting south to the Central Gulf Coast Monday into Tuesday. The Weather Prediction Center has issued a Marginal Risk for Sunday; and upgrades to a Slight Risk (level 2 of 4) on Tuesday across south-central LA to Mobile Bay mainly for risks near susceptible urban locations along I-10/12.  

The aforementioned Pacific airmass/frontal zone has cross much of the northern Rockies and has already developed a stronger surface low just north of the U.S. Canada border. Associated strong winds and snows is resulting in dangerous travel conditions across E Montana with a Blizzard Warning still in affect across far east-central MT until 6 pm MST Sunday. Downstream warm air advection will over-top some remaining colder air across northern MN into the Western Great Lakes Sunday night. Winter Storm warnings and advisories are in effect across the northern Red River Valley into northern MN where 4-7" of snow are expected.

Strong onshore flow off Lake Superior will further enhance local snow totals across the Arrowhead of MN range with 9-12"+ totals expected.  Behind the cold front a combination of cold air off the Pacific, as well as from eastern AK, Yukon will continue to filter southward directed through the Intermountain Region and Great Basin early this week. Below average temperatures will also bleed out in the Plains by late Monday into Tuesday with a classic 'Blue Norther' cold front driving well through the Southern Plains into northern Mexico by Tuesday. High temperatures will be about 5-10 degrees below normal across much of the Rockies, Southwest and eventually into the Plains.   

Perhaps most impactful, is the surge directed through the Great Basin into the lower Colorado River Valley will result in well above average high pressure that should allow for the front to cross the Peninsular Range Monday. This will bring very strong Santa Ana winds across southern California on Monday and given dry/low humidity conditions already in place; Red Flag Warnings have been issued for the eastern Transverse and all Peninsular Ranges from Monday into mid-week; as well as a Critical Fire (level 2 of 3) from the Storm Prediction Center. Winds of 35 to 45 mph in the valleys and gusts of 50 to 65 mph in the mountains will help expand any fires that do develop quickly and may reduce visibility with blowing smoke and dust adding to travel concerns in the region.