The system is set to close out a stormy 2020 while also ushering in the New Year.
A moderate snowfall is likely across a broad area of the Intermountain West and the Great Plains, where moisture on the cool side of the system will fall as snow. It comes just days after Minneapolis and the Upper Midwest were snarled by a blizzard that crippled travel.
Meanwhile, windy conditions and heavy rainfall are possible across the Mississippi River Valley, Appalachians and Eastern Seaboard toward the end of the week, while the threat of severe weather brews across portions of the Gulf Coast. Cities in the Carolinas such as Charlotte, Columbia and Charleston could be dealing with strong to severe thunderstorms, including the risk of tornadoes, by late this week.
A soaking in Central California
The nascent storm system was moving ashore in central California early Monday, bringing arcing bands of rain and even some thunderstorms to portions of the parched Golden State. A rare display of lightning visited the greater Los Angeles area overnight Sunday into Monday, with thunder rocking Anaheim, Santa Ana and the Sierra Madre mountains.
“Small hail and frequent lightning with brief heavy rain [were possible with the] line moving through much Los Angeles County,” wrote the National Weather Service around 1 a.m. Pacific time. A flood advisory was issued for the region as heavy rain accompanied thunderstorms despite temperatures in the 40s.
Where wintry weather is likely
Farther inland, in the higher elevations of Ventura and Los Angeles counties, mountain snow is anticipated, with six to 12 inches likely above 5,000 feet. This could affect the Interstate 5 corridor late on Monday.
Heavy mountain snow is likely, too, along parts of the Sierra Nevada east of Fresno; up to 16 inches were expected there. The precipitation is welcome in California, given that the state suffered its worst wildfire season on record during 2020, and much of the region is mired in drought conditions. Wildfires have kept erupting during December in Southern California because of the lack of rainfall and land-to-sea wind episodes that tend to create dangerous fire weather.
The same high-altitude pocket of frigid air and spin that’s resulting in the inclement weather will swirl southeast into Mexico during Tuesday and Wednesday, with the cold air in its wake contributing to snowfall from the Great Basin and Range in Nevada to parts of Utah and the Colorado Rockies. A plowable snow is likely in the lower elevations, while mountain communities could be looking at snows amounting to the double digits.
On Wednesday and Thursday, the upper-level disturbance will briefly overlap, or phase, with a secondary piece of energy diving out of Saskatchewan and Manitoba, their synergy resulting in wintry weather for much of the central and northern Plains and Corn Belt.
Moderate to heavy snow across the Intermountain West, Plains
Only a dusting of snow is likely Wednesday across much of Kansas, but the forecast is uncertain in Kansas City, where a slight southward jog of the storm could bring a more disruptive snow event into the metro area. Three to five inches are likely over most of Nebraska and central and eastern South Dakota, with isolated half-foot totals expected.
Four to six inches are currently predicted for Minnesota, including Minneapolis, as well as Wisconsin and parts of Michigan, including the Upper Peninsula. A heavier snowfall of up to 10 inches is favored in Iowa.
Unlike with last week’s storm system, the impending midweek storm will not combine the snowfall with gusty winds, thereby sparing the Upper Midwest another blizzard. Last week’s storm brought wind gusts close to hurricane force.
Where severe weather may strike
By Thursday, the core of the upper-level disturbance will be anchored over Texas, with southerly winds on the east side drawing a warm, humid air mass northward. It won’t get very far though — the warmth is likely to be halted by cold air to the north, but a pinch of mildness will briefly lap at the Tennessee Valley, Mid-Atlantic and Southeast.
In the “warm sector,” strong to severe thunderstorms could develop ahead of an approaching cold front. Meanwhile, a strengthening low-level jet, or river of swiftly moving air screaming north at a mile or so above the ground, will transport warmth and moisture from the Gulf of Mexico northward. That will also yield a change of wind speed and/or direction with height, or wind shear, which can lead to severe thunderstorms, including tornadoes.
That means the risk of an isolated tornado with some thunderstorms ahead of the cold front, and more scattered damaging winds and embedded tornadoes with a squall line that might form along the front.
On Thursday, eastern Louisiana, southern Mississippi and Alabama, and the Florida Panhandle are all in the zone of concern for potential severe weather, including regions primarily between interstates 10 and 20.
By Friday, the area to watch shifts northeastward into eastern Georgia as well as the Carolinas. Albany, Ga.; Savannah; Charleston; and Columbia, S.C., may be in the zone of greatest thunderstorm risk.
Heavy rain and flood threat
Even where strong thunderstorms don’t threaten, heavy rain will still bring a good soaking to tens of millions of Americans, particularly in two bull's-eyes — one that may take shape midweek to the north of the warm front in East Texas, Arkansas and perhaps western Louisiana, and a second in parts of the northern Appalachians and Northeast.
“The widespread nature of this event and a sustaining anomalous moisture feed [could cause] flash flooding and/or urban ponding … quickly … with multiple hours of intense rainfall,” wrote the Weather Service Weather Prediction Center.
A general two to three inches with localized five-inch amounts are possible between East Texas and the Mississippi River, tapering to an inch or two in the Mid-Atlantic.
East of the Appalachians, most of the rain will fall very late Thursday or on Friday. Washington, D.C., is just 0.2 inches shy of tying the record for its third-wettest year, meaning it will be down to the wire as to whetherThursday’s rainfall pushes the nation’s capital into elite territory. An impressive 57.34 inches have already fallen, compared to an average annual rainfall total closer to 42 inches.
The front will depart into the weekend, bringing a brief spell of chillier air before milder conditions return early next week.
Andrew Freedman contributed to this report.