Weather across America

(NATIONAL) An intense low pressure system to bring wind-swept heavy rain up the Eastern Seaboard, colder air to trigger lake-effect snow from west to east across the Great Lakes, and a couple of slow-moving oceanic storms in the Pacific to spread unsettled weather into the West Coast states.

The center of an intense low pressure system moved across northern Florida where new all-time lowest sea-level pressure values for December might have been established early Sunday morning (pending verification). This intense storm is now tracking just off the coastline of the southeastern U.S. and continues to deepen rapidly. A swath of moderate to heavy rain ahead of the storm center will continue to stream northward up the Mid-Atlantic states through Sunday night, reaching into New England by Monday morning. 

The warm and moist air surging northward from the Atlantic will sharpen a front near the coast ahead of the arrival of the storm center. This front will help focus the most intense rainfall to impact areas just to the west, while the strongest onshore winds from the east will impact areas near and just inland from the Mid-Atlantic coast through Sunday night. Thunderstorms with brief intense rainfall along with squalls can be expected to impact the coastal plains as well.  

By Monday afternoon, a double-barrel low pressure system is forecast to track more quickly northward into New England. The rain across the Mid-Atlantic states will taper off from west to east on Monday behind the storm center as wind-swept rain, heavy at times, overspreads the entire Northeast during the day on Monday. Meanwhile, colder air from central Canada will be pulled southeastward across the Great Lakes on Monday behind the big storm, triggering lake-enhanced snow from west to east across the Great Lakes and toward the Appalachians by later on Monday.  

Even though the big storm will begin to depart the Northeast Monday evening, the huge circulation of the storm will overspread the entire eastern U.S. with very blustery conditions. Snow showers and lingering lake-effect snow downwind from the lower Great Lakes are expected to gradually wind down as the day progresses on Tuesday, tapering off to flurries by Tuesday evening. Meanwhile, precipitation ahead of a large and slow-moving oceanic storm in the Pacific already reached California on Sunday. 

This system will continue to spread unsettled weather up the West Coast through Tuesday as another oceanic storm approaches in its wake later on Tuesday. Mostly rain is expected with this system. It appears that the higher terrain of northern California will receive the highest precipitation totals of more than two inches over the next couple of days. The reminder of the western and central U.S. will remain dry through Tuesday under a stable and expansive high pressure system. 

The entire country will remain milder than normal for this time of year before the surge of colder air from Canada brings below normal temperatures into the Ohio Valley and Florida Peninsula on Monday. In fact, record high temperatures are expected across New England on Monday as warm and moist air from the Atlantic surges into the region amid wind-swept heavy rain in the height of the big eastern storm. Colder than normal temperatures will then spread the southern and southeastern quadrant of the country including Florida on Tuesday.