|February 20 2023|
Coast to Coast Major Winter Storm: (2/20/22 - 2/23/23)
By: Peter Mullinax, WPC Meteorologist
On February 20, the upper level pattern featured an anomalous upper low off the west coast of Baja California, an impressive ridge off the Pacific Northwest coast, and deep troughing at 500mb over the Midwest. As the ridge over the northeast Pacific began to break down, a potent shortwave trough dove south towards the Pacific Northwest by the morning of February 21. Meanwhile, an area of Arctic high pressure was dislodged and directed south through the Canadian Rockies and down the Canadian Prairies. The arctic front was pushing south through the northern Rockies and High Plains throughout the day, leading to plummeting temperatures and bitterly cold wind chills in the front’s wake. The advancing upper trough would direct copious amounts of Pacific moisture at the West Coast at the same time as the left-exit region of a 150kt jet streak moves through the Northwest and into the Rockies. Combined with strong orographic upslope flow into numerous mountain ranges, periods of heavy snow broke out across many of the higher elevated areas of the West from the Cascades to the central Rockies.
By the early morning of February 22, the upper trough had significantly amplified and diffluent flow out ahead of a negatively tilted 250-500mb mean trough caused a surface low to rapidly deepen over southern Utah and the central Rockies. The 12Z surface analysis showed a 979mb low over southeast Utah. This area of low pressure broke the previous sea level record minimum for the month of February in places that include Cedar City, UT, Flagstaff, AZ, and Grand Junction, CO. The site with the lowest observed pressure was Leadville, CO which dropped to 976.3mb. Farther north, the arctic front raced south into not only the central Rockies, but through the central Plains and the Great Lakes as well. Record cold daily lows were set in the High Plains of WY and CO, while an even larger footprint of record cold maximum temps were observed from the West Coast to North Dakota.
While the strong upslope enhancement and funneling of Pacific moisture continued to produce heavy mountain snow in the West, the amplifying trough in the West combined with strong upper level ridging over Florida led to the development of a robust 60 knot jet low level jet across the Middle Mississippi River Valley the morning of February 22. In addition, the upper low that was originally near Baja California merged with the amplifying upper trough over the West and entered the southern High Plains. The strong warm air advection (WAA) running into the arctic front draped across the Midwest resulted in strong vertical motion aloft and the subsequent development of snow from the Dakotas to the Upper Midwest. Farther south across southern WI, the Great Lakes, and the Northeast, surface temperatures were below freezing but the aforementioned low level jet caused a burgeoning warm nose at low levels, causing snow to melt and fall in the form of sleet and/or freezing rain. The upper trough in the west was slower to eject east, causing a favorable setup for a prolonged period of accumulating ice in these areas.
From the afternoon of February 22 into the early morning hours of February 23, heavy snow falling over the Northern Plains and Upper Midwest transitioned from a longer duration WAA setup to having an emerging 850mb low tracking across the Missouri River the night of February 22 and ending up over the Mississippi River by 12Z February 23. The deformation zone on the northwest flank of the 850mb low led to 1-2”/hr snowfall rates late February 22 into the morning of February 23. Meanwhile, an elongated frontal boundary stemmed from the primary low in the Midwest to a developing area of low pressure off the Northeast coast. This led to the formation of an elongated and moist easterly flow north of the front across the Great Lakes and Northeast. After a wintry start to February 23, a dry slot in the 300-700mb layer began to shut off the heaviest snowfall. This caused the heaviest snowfall to be confined to Michigan’s Upper Peninsula and northern New England. In the storm’s wake, the dome of arctic high pressure centered itself over the Midwest by the morning of February 24 when its observed highest pressure of 1046mb was responsible for widespread record cold minimum and maximum temperatures from the West Coast to the Upper Midwest.
Snowfall amounts were highest from the northern Rockies to the Great Lakes. Totals in portions of Wyoming, South Dakota, Minnesota, Wisconsin, and Michigan reported over a foot of snow with localized amounts that eclipsed 20”. This did lead to dangerous to even impossible travel conditions, which included having stretches of I-90 and I-94 in Wisconsin and Minnesota closed due to heavy snow. In the Northeast, most totals ranged between 5-10” with the higher totals focused across northern New England. Schools were closed and travel was treacherous in impacted areas. In terms of ice accumulations, areas from the Midwest to the northern Mid-Atlantic reported anywhere from 0.25-0.75” of ice with the highest reported amount near Frankville, WI where 0.75” of ice accumulation was measured. The crippling ice accumulations were responsible for over 900,000 customers losing power in the Midwest alone with sporadic outages also reported in the interior Northeast. The NWS Detroit mentioned in a review of the event that “numerous reports of downed tree limbs were reported making some roads impassable.” NWS Detroit also stated that “for many metro Detroit communities, an ice storm with this wide of a footprint has not been observed since April 2003.”
Strong winds were also associated with this winter storm, leading to the issuance of Blizzard Warnings in portions of Wyoming, the eastern Dakotas, and central Minnesota, including the Twin Cities metro area. The combination of 1-2”/hr snowfall rates and wind gusts exceeding 40 mph led to whiteout conditions and snow drifts measured in feet. The winter storm forced the Minnesota legislature to close, and it also contributed to the cancellation of more than 1,600 flights.