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Extreme Temperature Diary- Saturday November 25th, 2020/ Main Topic: American Cold Wave Naming Rules for This Winter – Guy On Climate

Week’s third storm to charge across U.S. with another blizzard, tornadoes

The third storm in just six days may be the most intense amid an exceptionally active weather pattern

By Matthew Cappucci

Back-to-back storms have already pummeled the Lower 48 states, bringing heavy snow, deadly tornadoes, flooding rains and power outages. More than a half-million customers in the eastern United States remained in the dark to start Wednesday after Monday and Tuesday’s high-impact storm.

Unfortunately, a third storm system is already beginning its march across North America, unleashing blizzard conditions in the Pacific Northwest. By Thursday, it’s poised to dive into the Plains and spread snowfall. That’s before it unleashes severe thunderstorms and tornadoes in the South and blizzard conditions in parts of the Upper Midwest and Great Lakes on Friday. A quick burst of heavy rain will also sweep across flood-prone areas of the Mid-Atlantic and Northeast late Friday into Saturday.

Like the storm that barreled across the central and eastern United States on Monday and Tuesday, this next cyclone will generate an enormous area of high winds that could trigger tens of thousands of power outages in multiple states. In fact, computer models project its pressure will drop faster than the early-week storm and that it will meet the criteria of a “bomb cyclone” because of its rapid intensification. Generally, the lower the pressure, the stronger the storm.

How the storm will evolve

After ejecting from the Rocky Mountains on Thursday, the storm system will begin to intensify over the Plains. Severe thunderstorms will erupt on its warm side, first over Texas, Arkansas and Louisiana on Thursday before spreading into Alabama and the southeast on Friday. Both days could feature a tornado risk, with strong tornadoes not out of the question Friday.

On the system’s cold side, another swath of heavy snow falls in the Midwest from Thursday night to Friday night. The jury is still out on how much snow falls where, but St. Louis, Kansas City, Chicago and Detroit could see appreciable amounts. Where jackpot totals occur, a foot or more is possible. Fierce winds accompanying the snow could bring near-whiteout conditions for some.

On the storm’s back side, the coldest air of the winter will plunge into the western and central states this weekend, and heavy lake-effect snows could occur downwind of the Great Lakes, including near Cleveland and Buffalo.

Another winter storm could threaten the East Coast by the start of next week.

Pacific Northwest snow and wind

Blizzard warnings were in effect in the Cascades until Wednesday evening, with winter storm warnings covering most of the remainder of Idaho and Oregon and even dipping into the northern Sierras in California. Snow levels in northern areas were reaching down to 2,000 feet, combining with strong winds topping 40 mph to reduce visibilities below a quarter-mile. Wind gusts could approach 75 mph in some of the highest mountain peaks. The high terrain of Northern California and the Great Basin of Nevada are in line for wintry weather, too.

Here are some of the peak totals through Tuesday night:

  • Steven’s Pass, Wash: 30 inches
  • Paradise, Wash: 19 inches
  • Roslyn, Wash: 18 inches
  • Snoqualmie Pass, Wash: 18 inches
  • Dover, Idaho: 13 inches
  • Mount Baker, Wash: 13 inches
  • Elmira, Idaho: 12 inches

Up to about 10 inches of snow also fell over Washington’s Olympic Range closer to the coast, where a blizzard warning is in effect, as well. Another 3 to 6 inches is possible throughout the daylight hours Wednesday before the storm system withdraws to the southeast.

High winds have buffeted much of the region. In Kennewick, Wash., near the Oregon border, gusts up to 77 mph were recorded. In Seattle, winds gusted 40 to 50 mph, but gusts approached 70 mph at the coastline along the Strait of Juan de Fuca.

Potential blizzard for the Midwest and Great Lakes

A computer model blend simulates how much snow could come down with the next storm. (WeatherBell)

It’s too early to know how much snow will fall as the same storm system spawns a new region of low pressure over the Plains, but it’s looking like a lot. Weather models are consistent in dropping a foot or more across the nation’s heartland, but they differ on the exact placement of the top totals.

Snow looks to break out over Kansas, Nebraska and/or portions of the Corn Belt on Thursday afternoon or evening. Then it increases in coverage and intensity while shifting northeast, reaching Chicago and perhaps Detroit on Friday. North of the rain-snow line, significantly more than a foot of snow isn’t impossible.

“Several inches of accumulating snow in combination with strong winds may result in difficult travel across the area into Saturday,” the National Weather Service in Chicago wrote, “although considerable uncertainty remains regarding the storm track and rain/snow line location.”

It’s possible that mild air off Lake Michigan cuts down on snow totals in Chicago, but much greater amounts fall just to its north and west.

Even after the storm passes, frigid air spilling southward over the Great Lakes will bring heavy lake-effect snow on downwind shores over the weekend.

“The pattern supports the possibility of significant snow amounts through the later half of the weekend for area east of the lakes,” wrote the Weather Service office serving Buffalo. “Additionally, windy conditions will persist throughout the weekend and support areas of blowing snow.”

Tornadoes in the South

The same storm system will swing a combination cold front across the lower Mississippi Valley and southeast. Near the front, a swift change of winds speed and/or direction with height, fueled by a fierce jet stream dip, will encourage those thunderstorms to spin and produce tornadoes. Some of the strong momentum in the upper atmosphere could also be mixed to the surface in the form of damaging straight-line wind gusts.

The National Weather Service Storm Prediction Center has drawn a Level 2 out of 5 “slight” risk of severe weather over portions of Texas, Arkansas and Louisiana for Thursday. It includes cities in East Texas such as Tyler and Lufkin, as well as Shreveport in northern Louisiana and cities south of Little Rock.

Friday is more concerning. The agency has taken the unusual step of drawing a Level 3 out of 5 “enhanced risk” of severe weather three days in advance, accounting for what it warns could be “high winds and a few strong tornadoes.” The area stretches from near a line from Birmingham to Montgomery, Ala., east toward Savannah, Ga., and northeast through the Carolina Piedmont south of Raleigh, N.C.

It’s unclear which structure of severe thunderstorms will form. Rotating supercells with a couple of tornadoes are possible, or clustered storms more prone to producing straight-line winds could materialize. Either scenario would be problematic.

Heavy rain and strong winds in the East

Fortunately, it does appear that, for most areas in the southeast, this storm may feature less rainfall than several of the recent systems. That’s encouraging, since the ground is already so waterlogged from a month and a half of excessive rains. For the southeast, the convective nature of the rainfall, meaning more scattered in the form of thunderstorms and individual downpours, will lead to irregular and highly variable precipitation totals. Some spots might see only a half-inch of rain, while others get 2 or 3 inches in a short period.

How to prepare your home for extreme cold, and stay warm in a power outage

Like its predecessor, this storm will also contain strong wind gusts. Gusts of 50 mph are likely along the Interstate 95 corridor from North Carolina to Maine, with a few gusts of 60 mph along the immediate coastline of Long Island, parts of Connecticut, Rhode Island and southeastern Massachusetts. Down East Maine will also see some very strong gusts. More power outages seem inevitable.

Frigid weather in storm’s wake

On the storm’s back side, the coldest air of the winter will plunge southward. The most bitter air is forecast to target the zone from Montana to the Texas Panhandle, where temperatures will be at least 30 to 40 degrees below normal over the weekend.

By Tuesday, the Weather Service projects subzero cold from Montana to Missouri.

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