Snow fell from late evening December 26 to early afternoon December 28. The snow was particularly wet and dense for most of the event through late evening December 27. Heaviest snow with snowfall rates around an inch per hour fell from 5 PM to 10:30 PM December 27 with the approach of the core of the mid to upper level (700 mb to 500 mb ) part of the storm system. A strong surge of warm air from the south caused snow to mix with or change to rain in Superior, WI and at the lakefront in Duluth from around daybreak into the afternoon. Precipitation turned back to snow late afternoon and evening. Precipitation just inland in Duluth stayed mostly or all snow, especially over the hill. Temperatures a few degrees above freezing, even in the higher elevations, held back accumulations. Even so, snow accumulated 10 to 15 inches along and inland of the ridge crest, including 13.1 inches at the National Weather Service. Lesser accumulations occurred at lower elevations.
Dashed blue lines indicate temperatures at or below zero degrees centigrade (freezing). Dashed red lines indicate temperatures above freezing. The warm advection was particularly strong at 850 mb from 6 PM, December 26 to 6 AM December 27. Strongest warming at 925 mb occurred between 6 AM and 6 PM, December 27.
925 mb pressure charts - Storm Prediction Center upper air map archive
6 PM CST December 26, 2018
6 AM CST December 27, 2018
6 PM CST December 27, 2018
850 mb pressure charts - Storm Prediction Center upper air map archive
6 PM CST December 26, 2018
6 AM CST December 27, 2018
6 PM CST December 27, 2018
Surface maps - Weather Prediction Center
6 PM CST December 26, 2018
12 AM CST December 27, 2018
6 AM CST December 27, 2018
12 PM CST December 27, 2018
6 PM CST December 27, 2018
12 AM CST December 28, 2018
6AM CST December 28, 2018
500 mb pressure charts - Storm Prediction Center upper air map archive
6 PM CST December 26, 2018
6 AM CST December 27, 2018
6 PM CST December 27, 2018
6 AM CST December 28, 2018
