For the remainder of Tuesday, an upper-level wave will continue to track through the northern Intermountain West supporting some moderate snowfall across the Northern Rockies this evening.
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Concurrently, a surface low near the Black Hills of SD and portions of E MT/WY will start to strengthen and merge with the associated Pacific cold front, lifting a warm front northward across the central Plains sparking the potential for a few isolated severe thunderstorms.
The Storm Predication Center (SPC) has a broad Marginal Risk in the vicinity of the low and southward into the central High Plains just ahead of a strengthening dry line.
Further south, the strengthening winds and very dry ground conditions will continue to support a broad Critical Fire Weather area issued by SPC, with a large area of New Mexico, Eastern Colorado, Western Nebraska, Western Kansas and parts of the OK/TX panhandles already under Red Flag Warnings.
This risk will continue as the strong Pacific flow over-topping the Central Rockies will keep winds and relative humidity low through Wed into Thursday as well.
Into the overnight period (Tues into Wednesday), the surface low will continue to lift north, strengthen and have the potential for producing moderate to occasionally heavy snow fall across far eastern MT, and western/northwestern North Dakota, peaking Wednesday morning, but likely to continue throughout the remainder of the day into early Thursday morning.
As the main upper-level energy emerges into the northern Plains on Wed, the risk for severe weather increases in coverage/intensity, as the SPC has issued a Slight Risk along/ahead of the cold front and dry line from eastern Nebraska into Iowa and southward across central/eastern Kansas into western Oklahoma.
Large hail and high winds are the greatest potential, though an isolated tornado or two remain possible, with highest potential across central Kansas.
As the thunderstorms expand in coverage into the early overnight period, thunderstorms will pose a risk of excessive rainfall/flash flooding mainly north and east of the SPC Slight Risk, given areas of Iowa, southeast Minnesota, Wisconsin soils more saturated and have seen recent snow melt.
As such, the Weather Prediction Center (WPC) has issued a broad Marginal Risk to account for heavy rainfall over these saturated areas resulting in isolated to widely scattered flash flooding potential into Thursday morning.
Elsewhere, a very broad large scale low dominates southeast Canada resulting in large area of increased cloud cover across the Northeast, keeping temperatures at or below average today into tomorrow.
South of the cloud area in the Mid-Atlantic, clearer skies and drier air (along with drier than normal soils/vegetation) will see increased temperatures in the 70s and 80s into Wednesday.
The combination has resulted in increased fire weather concerns, with the SPC issuing a Critical Fire area across the Piedmont of Virginia with a surrounding Elevated Risk over the remainder of the state and portions of adjacent Maryland, West Virginia, Delaware and far northeast North Carolina.
Red Flag Warnings are up for much of the Elevated area for today, Tuesday. ■
Modified arctic air combined with a moisture-laden area of low pressure along the Gulf Coast will continue to allow for a broad area of winter weather impacts from the Lower Mississippi Valley to the Southeast today into early Saturday morning.