A frontal system will continue to move through the West Wednesday-Thursday with accompanying heavy rainfall in California and moderate to locally heavy snowfall in the mountains as Pacific moisture overspreads the region.
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Rainfall totals in California Wednesday will likely be lower than Tuesday and with prior systems that have impacted the region.
However, given the very wet antecedent conditions, there is a Marginal Risk of Excessive Rainfall (level 1/4) along the coast as a couple rounds of storms with moderately heavy rain rates may lead to some localized flooding concerns in terrain sensitive and urban areas.
Moderate to locally heavy snow is also forecast to continue for the Sierra and higher elevation mountain ranges across the Great Basin Wednesday, spreading into the Northern and Central Rockies on Thursday.
Little to no snow accumulations are currently forecast for most lower elevation valley locations, though there is a chance for a few inches of snow in the Northern High Plains Thursday.
Winds will also be quite gusty Wednesday as the Pacific front pushes through the Interior West, with wind-related advisories out from southern California into the southern Great Basin and Desert Southwest.
These high winds are forecast to continue into the Southern Rockies on Thursday, with gusts upwards of 70 mph possible.
Well below average highs in the 40s and 50s for the western Great Basin and California Wednesday will spread further east into the eastern Great Basin Thursday following the passage of the Pacific front, with highs dropping into the 60s for the Desert Southwest.
Highs will remain more seasonable in the Pacific Northwest, with 50s and 60s forecast.
Meanwhile, a fast moving upper-level shortwave and accompanying surface cold front will pass through the Interior Northeast Wednesday bringing a chance of snow showers.
While any snow accumulations are not expected to be particularly high, the snow that does fall is expected to come with snow squalls producing brief very heavy snow rates and gusty winds, leading to rapid onset whiteout conditions and dangerous travel.
In addition, there is the potential for a flash freeze as temperatures quickly fall behind the cold front, leading to icy roads and slippery conditions.
Generally seasonable high temperatures in the 40s and 50s for New England and the 50s and 60s for the Mid-Atlantic Wednesday will fall into the 30s and 40s for New England and the 40s and 50s for the Mid-Atlantic Thursday.
Temperatures will remain well below average and quite chilly in the presence of a cold Canadian airmass behind the front over the Northern Plains and Upper Great Lakes.
Highs on Wednesday are forecast to only reach the 20s and 30s, with lows Thursday morning falling into the single digits for many locations.
A warm front moving northward into the region will significantly warm up temperatures from South Dakota eastward into the Lower Great Lakes, with highs into the 50s and 60s, while temperatures remain frigid to the north.
The frontal system pushing through the West will enter the High Plains Thursday afternoon as a lee cyclone organizes over the Central High Plains, with a dryline extending southward over the Central/Southern Plains.
Warm, moist return flow from the Gulf will push northward following a warm front into the Central Plains and Midwest.
These features will be the focus for increasing precipitation chances in the region.
To the north, some moderate to locally heavy rainfall is possible late Thursday evening into early Friday morning with storms forming along the advancing warm front over the Midwest.
There is a Marginal Risk of Excessive Rainfall as the potential for storms to repeatedly move over the same locations in the vicinity of the front may lead to some isolated flash flooding concerns.
At the same time, a cold front pushing southward from Canada will help to reinforce the colder airmass north of the front as increasing moisture streams in from the south.
Some light to moderate snow accumulations will be possible overnight Thursday from North Dakota into the Upper Great Lakes.
A few isolated thunderstorms are also possible along the dryline, with the Storm Prediction Center highlighting portions of central Oklahoma and northwest Texas for a Marginal Risk (level 1/5) of severe weather.
Moderate buoyancy, strengthening winds aloft, and a low level jet developing Thursday evening will provide the necessary ingredients for any storms that do form to pose a risk for hail, gusty winds, and a tornado.
Further west behind the dryline over the Central and Southern High Plains, very strong, gusty downsloping winds will lead to warming temperatures on top of very dry conditions, prompting a Critical Risk of Fire Weather from the Storm Prediction Center.
Generally cool highs in the 50s and 60s across the Central/Southern Plains into the Mississippi/Ohio Valleys and Southeast on Wednesday will warm up into the 70s Thursday as the warm front lifts northward.
The downsloping flow over the Central and Southern High Plains will send highs into the upper 70s and 80s Thursday. ■
The upper-level pattern over the CONUS will remain rather stagnant the next couple of days with lows over the Northeast and California and ridging in between.