Blizzard — Minnehaha, South Dakota

2020-12-23 · Minnehaha, South Dakota

Event narrative

Winds gusted as high as 63 mph near Dell Rapids and 62 mph at Sioux Falls, and despite a lack of pre-storm snow cover, snowfall which accumulated to 4.5 inches 6 miles south of Hartford, 3.0 inches at Colton and 2.8 inches at Sioux Falls resulted in widespread whiteout conditions for several hours. Travel was not advised during the blizzard across all of southeast SD. At 1141CST, fifteen vehicles collided in whiteout conditions on northbound Interstate 29 around mile marker 99 which closed the road for 7 hours and resulted in 6 indirect injuries. At 1252CST, another 30 vehicles crashed on westbound Interstate 90 three miles west of Sioux Falls (mile marker 393) which closed the roadway for 8 hours and resulted in 5 indirect injuries. Another multi-car collision occurred on Interstate 29 in Sioux Falls, which was just one of several dozen other accidents. All air traffic was cancelled for December 23 at Joe Foss Field in Sioux Falls.

Wider weather episode

Conditions with temperatures at record or near-record warm levels on December 22 underwent a drastic change over a brief 24 hour period, as a sharp upper-level trough in westerly flow amplified while translating from the Pacific Northwest to the Plains. Low pressure developed and deepened rapidly while moving from South Dakota around 0000CST December 23 to the northern Great Lakes by 0600CST December 24.

Very steep lower to mid-level lapse rates and lift focused within a 200-250hPa deep layer supportive of effective dendritic growth resulted in intense precipitation banding over a 5 to 8 hour period. Winds in the lower mixed layer reached 40 to 60 knots as Arctic air surged into the area behind the system, producing numerous hours of widespread whiteout conditions.

Source: NOAA Storm Events Database, event_id 934458. Narrative written by the NWS forecast office that issued the report.