|April 23 2022|
Late April Northern Rockies & Plains Winter Storm: (4/22 - 4/24)
By: Peter Mullinax, WPC Meteorologist
The second in a pair of April winter storms tracked across the northern Rockies and northern High Plains between April 22-24. This storm system's origins began as a potent upper low off the West Coast on April 21 and eventually tracked over the West Coast by the morning of April 22. At 250mb, a sharp upper level trough provides large scale vertical ascent over the Intermountain West. In addition, sufficient moisture at 700mb and plummeting temperatures aloft associated with height falls from the approaching upper trough allowed snow to be the primary precipitation type from the Great Basin and Wasatch to the northern and central Rockies. Meanwhile, in the Great Plains, a robust 850mb low level jet was escorting a steady stream of low level moisture into the Northern Plains with the 12Z April 22 850mb upper-air map identifying an 850mb jet as strong as 60 knots in southwest Kansas. This was is possible due to a strong ridge of high pressure in the Southeast (1030mb on the 12Z surface map April 12) and deepening wave of low pressure in eastern Utah. Between the surging low level moisture plume in the Great Plains, the strong synoptic scale ascent ahead of the upper trough in the West, and sub-freezing temperatures aloft plunging south, the stage was set for of periods of heavy snow to envelope the Northern Rockies the afternoon of April 22 and into the overnight hours in the northern High Plains. Beneath this deformation zone is where snowfall rates of 1-2"/hr transpired with similar rates also occurring in the higher elevations of southern Montana, central Wyoming, and as far south as the northern Colorado Rockies.
By the morning of April 23, the 250mb trough had taken on a negative tilt over the central Rockies and a 500mb closed low was deepening east of the Wyoming Rockies. The 12Z surface analysis showed a 987mb low over south-central South Dakota with a comma head shaped IR satellite cloud shield overtaking a stretch of land that included the northern Rockies, the northern High Plains, and the Upper Mississippi River Valley. The deformation zone was clearly identifiable on the 700mb upper air chart where a protruding area of 700mb moisture was located over the Black Hills of South Dakota, the High Plains of the western Dakotas, and over both eastern Montana and Wyoming. Winds whipped up towering snow drifts and caused blizzard conditions throughout the western Dakotas with maximum wind gusts ranging between 60-80 mph. In addition, there were reports of accumulating freezing rain that helped put additional weight on trees and power lines, as well as making travel more dangerous. The upper low continued to deepen heading into April 24 with an occluded surface low positioned in far southeast North Dakota that morning. The storm began its gradual weakening phase throughout the day as the upper air charts indicate the closed lows at 850mb, 700mb, and 500mb had become vertically stacked on 12Z April 24. A cold conveyor belt persisted on the backside of the cyclone, which as of 12Z was located over east-central North Dakota. The 850 mb moisture feed was relaxing throughout the day, but enough moisture was present to produce periods of moderate to heavy snow west of Grand Forks and Fargo. The storm continued its track northeast with light accumulations in parts of northern Minnesota and the remainder of the Northern Plains. By the morning of April 25, the storm had tracked into eastern Ontario and aside from light snowfall in the Upper Great Lakes, the snow storm had concluded across the northern High Plains.
Regarding the forecast, signals for a potential winter storm were present as far out as seven days. Confidence really began to grow by Day 5 when 50-70% probabilities for >0.25" of liquid equivalent snow/sleet were forecast in the northern Rockies and High Plains. Four days out, probabilities ballooned to 70-90% in these same areas. Eventually by Day 2, WPC snowfall forecasts indicated a >70% probability swath for snowfall totals of at least 12" for April 23 from western North Dakota and eastern Montana into northeast Wyoming and far western South Dakota. Other products, such as the Winter Storm Severity Index (WSSI) were forecasting "Extreme" impacts one day before the storm's arrival. Widespread Blizzard Warnings were issued for much of the northern High Plains while Winter Storm Warnings and Winter Weather Advisories were in place for parts of the northern and central Rockies.
Snowfall totals up to two feet fell in the higher elevations of the central and northern Rockies while totals of 12-20" were common in the northern High Plains. According to the final WPC Storm Summary for this system, the highest reported snowfall amount came from Lead, SD (located on the northern slopes of the Black Hills) where the town measured 22" of snowfall. About 18 miles southeast of Gallatin Gateway, MT, there was a reported 20" of snowfall by the time the snowstorm exited the region. In Wyoming, the towns of Burgess Junction and Gillette both reported 19" of snow. Lastly, in North Dakota, 18" of snow accumulated just west of Niobe. The combination of heavy snowfall and gusty winds, along with the weight of the wet snow, led to thousands of customers losing power. At one point, roughly 20,000 were without power and some would not get power back for almost a week after the storm had subsided. In terms of travel, select sections of I-94 and I-90 were closed due to treacherous travel conditions Saturday night and remained closed into Sunday morning. According to a review from the Bismarck WFO, Williston Basin International Airport lost power and had to close the runway due to near zero visibility and drifting snow. The Red Cross also opened warming shelters in the towns of Williston, ND and Crosby, ND. Treacherous travel was also common in the northern and central Rockies with some road closures reported in parts of Wyoming and Montana.
This snowstorm capped off what was an incredibly snowy month of April, especially in North Dakota. Two miles northeast of Grassy Butte, ND, the area reported 16" during this storm and 22" from the blizzard from April 12-14, bringing the monthly total from those two storms to 38". The significant snowmelt and periods of rainfall that ensued in the days following the blizzard led to some instances of flooding in low lying areas across western and central North Dakota in the final week of April.