Weather across America

(NATIONAL) Flash flooding and severe weather threats over the southern High Plains will gradually lessen and shift toward southern Texas, unsettled and windy weather will spread from the Great Lakes to New England, and cold air plunges south into much of the eastern two-thirds of the country while near record warmth persists across the Northwest.

An upper-level low moving into the Southwest continues to trigger scattered to widespread showers and thunderstorms from Arizona eastward to Texas and Oklahoma.  Meanwhile, cold air from the north will begin to push southward across the southern Plains.  

The interaction between these two systems will gradually shift the threat of heavy rain and strong to severe thunderstorms from across the southern High Plains Sunday evening to mainly across southern Texas by Monday night. A slight risk of excessive rainfall leading to flash flooding is expected from southeastern New Mexico into the Big Bend region of Texas through early Monday morning. 

Heavy rainfall is forecast to shift into southern Texas later on Monday, but the risk for flash flooding will be marginal due in part to dry soil conditions.

Farther north, an increasingly cold, windy, and unsettled weather pattern is forecast to develop across the northern portion of the country before spreading east into the Northeast over the next couple of days.  

An anomalously cold air mass will surge southward across the Great Lakes behind an intensifying low pressure system. This system will in turn be energized by periodic reinforcing shots of colder air from central Canada. Rain initially across the upper Great Lakes is forecast to change over to mixed precipitation as the cold air arrives later Sunday.  

Meanwhile, scattered thunderstorms are expected to move across the central Appalachians to the Mid-Atlantic near the trailing cold front into Monday morning.  

By Monday afternoon, portions of interior New England may see a quick round of heavier rain and possibly thunderstorms as a warm front lifts through the region, together with a low pressure wave intensifying along the sharp front. The vigor of the front ahead of the intensifying low near the Great Lakes will bring rounds of showers and thunderstorms through Tuesday across New England leading to a threat of heavy rain by later on Tuesday.  Colder air will gradually arrive from the west behind the front.  

Freeze watches and warnings are in effect from the central High Plains eastward through the mid-Mississippi, Tennessee and Ohio Valleys toward the Appalachians in anticipitation of this early season cold surge.  Much of these areas will experience the first freeze of the season by Tuesday morning, with readings 15-20 degrees below normal.

Farther south, clouds and precipitation associated with the upper low in conjunction with cooler air from the north will keep high temperatures into the 50s and 60s across much of the southern Plains into Monday before drier air arrives on Tuesday. An upper ridge indicative of anomalous warmth will move across the Northwest over the next several days, in stark contrast to the cold in the eastern two-thirds of the country.  

Highs in the 70s and 80s in the Pacific Northwest will be 15-25 degrees above average, and potentially record setting through midweek.