Orographic Blizzard, Duluth, MN

December 24 to 26, 2009

A major snowstorm, including blizzard conditions, occurred on Christmas Eve and Christmas Day. At its peak, during the overnight morning hours of Christmas Day, the storm produced snowfall rates of 2 inches per hour and wind gusts over 40 mph. Visibilities easily dropped below 1/4 mile. Later in the morning after sunrise, winds gusted over 50 mph but the precipitation was mixing with or changing to rain and sleet, especially near the immediate lake shore. East winds converging into the head of Lake Superior and rising up the higher terrain (orographic lift) greatly enhanced snow totals. The longer duration of mixed precipitation in the lower elevations near the lake held back accumulations considerably in those areas. Cooling due to upslope winds likely helped keep precipitation in the form of snow for a longer period of time in the higher elevations. Snow totals ranged from around 15 inches near the lake to around 24 inches farther inland, including 24.5 inches at the National Weather Service office.

The extent of heavy snow and mixed precipitation produced by the storm is illustrated by the watches and warnings issued by the National Weather Service. Red represents Blizzard Warnings, including at the western tip of Lake Superior. Pink indicates Winter Storm Warnings.

Sample of NWS/SPC Watches and Warnings Issued for the Storm

NWS Duluth, MN Radar near Peak of Storm

NWS Radar Mosaic

Water Vapor Satellite Image - NOAA GOES