Weather across America

(NATIONAL) Widespread rain and snow across the West, a wintry mix and much colder temperatures spread across the Plains and Upper Midwest, and flash flooding and severe weather expected in the Lower Mississippi Valley.

A deepening upper-level trough and accompanying surface frontal system will continue across the country early this week and lead to widespread impactful weather, from snow and high winds to the potential for flash flooding and severe weather. The system, currently moving through the Intermountain West and Pacific Northwest, will first continue to spread snow across the Great Basin and Rockies in the Intermountain West with lower elevation rain and higher elevation snow for the Pacific Northwest.

Snow totals look to remain on the lighter side in the valleys and lower elevations, with a couple inches or so possible. However, heavier snow is forecast at higher elevations in the mountains. Winter weather-related advisories are in effect for the Cascades and portions of the Northern and Central Rockies where totals broadly will range between 4-8 inches, with locally higher amounts over a foot. 

Stronger winds mixing down from the energy aloft as well as the passage of a cold front will also lead to the risk for high winds for portions of the Northern and Central Rockies and adjacent High Plains. Wind-related advisories are in effect for sustained winds ranging between 35-55 mph and gusts potentially as high as 80 mph.

The high winds may also lead to some dangerous travel conditions even where snow accumulations will be light due to blowing snow. These winds should last into early Monday morning further south. Another system moving into the Pacific Northwest later Tuesday may result in some snow at the lower elevations of the Pacific Northwest, including the I-5 urban corridor, but there is more uncertainty with the timing and accumulation potential as we get later into the forecast period.

Winter weather chances along with frigid temperatures will accompany the storm system as it moves into the Plains. Snow will first begin for the Central High Plains Monday morning and then spread northeastward across the Central Plains and into the Upper Midwest through the day Monday and into Tuesday following the passage of a cold front. 

Snow accumulations should remain light across the Central Plains but will likely be higher for portions of the Central High Plains/Black Hills as well as for portions of the Upper Midwest in the Lake Superior vicinity, where Winter Storm Watches have been issued for 4-6 inches of snow expected on Tuesday.

In addition to the snow, much colder, frigid temperatures are forecast to follow the cold front. Highs in the teens and 20s are forecast for the High Plains of Montana Monday and will spread rapidly across the Central and Northern Plains behind the front Tuesday.

Widespread showers and thunderstorms are expected ahead of the cold front on the warm side of the system Tuesday from the Lower Great Lakes/Midwest south through the Ohio/Middle Mississippi Valley and into the Southeast/Lower Mississippi Valley. Deeper Gulf moisture spreading northward ahead of the front across the Lower Mississippi Valley will lead to more intense, heavier rainfall rates. There is also the likelihood storms will move parallel to the cold front, repeating over the same locations, leading to heavier rainfall totals. A Slight Risk of Excessive Rainfall is out for portions of this region across eastern Louisiana, Mississippi, and western Alabama were these higher rain rates and totals may lead to scattered instances of flash flooding. 

Additionally, the increasing Gulf moisture along with very strong upper-level dynamics/increased wind shear associated with the storm system will combine to increase the chance for numerous severe thunderstorms. The Storm Prediction Center has issued an Enhanced Risk of severe weather for portions of the Mid-South/Lower Mississippi Valley for the risk of tornadoes, some potentially strong, as well as high winds.

Meanwhile, further east, showers will linger through Sunday night into early Monday across the Mid-Atlantic and Northeast as a storm system exists the region. A light wintry mix is likely for the Interior Northeast Monday morning as colder air moves into the region behind a cold front.

High temperatures are forecast to be around or above normal for late November as warmer air surges northward ahead of the cross-country storm system. Temperatures on Tuesday in particular will be running 10-20 degrees above normal for much of the central and eastern U.S., with 70s across the South, 60s in the Middle-Mississippi and Ohio Valleys, and 50s for much of the Great Lakes region. While Southern California and the Desert Southwest will likely avoid most of the precipitation chances the next couple of days, cooler than normal temperatures in the 50s and 60s will still follow the passage of a cold front.