Storm total snowfall. Click image to enlarge.
Satellite image of snow cover, December 2. Click to enlarge.
Widespread freezing rain and sleet affected many locations in central Illinois west of I-57 on Thursday November 30. Eleven counties in central Illinois reported ice ranging from a quarter to 2 inches thick, with the thickest ice around Decatur, Talorville, Clinton and Mount Pulaski. Eight counties reported heavy sleet ranging in depth from a half to 2.2 inches. This icy precipitation resulted in numerous traffic accidents, downed several large tree limbs and power lines, which resulted in power outages for several days in some spots.
The mixed precipitation changed to snow Thursday night and early Friday morning of December 1 and ended by noon Friday. The heaviest snow occurred along and west of the Illinois River, where snow accumulations were 8 to 16 inches. Areas east of the Illinois River, especially along the I-55 corridor had snow amounts ranging from 3 to 8 inches on top of the ice and sleet. The snow and ice accumulations got about as far east as I-57.
Synoptic Setup (written by forecaster Matt Barnes):
A strong cold front moved into west-central Illinois during the afternoon of November 29, accompanied by a band of showers and thunderstorms. This front slowly pushed toward the Illinois-Indiana border by the morning of November 30, bringing an abrupt end to the much above normal temperatures the Midwest had been experiencing for the past week. Readings steadily fell during the day, causing light rain to change to freezing rain across locations along and west of I-57 by late in the day. Some minor ice accumulations were noted during the day, particularly on trees and other elevated surfaces.
At the same time, a potent upper-level disturbance tracking across the southern Plains aided in the formation of an area of low pressure along the southern edge of the front. Strong jet streaks across the Great Lakes and lower Mississippi Valley interacted with one another to produce impressive upper-level divergence, which led to a rapid deepening of the surface low. As a result, the low intensified from 1006mb across eastern Arkansas at 6PM to 998mb across western Kentucky by midnight. Ample Gulf moisture flowed northward ahead of the strengthening system, resulting in a marked increase in precipitation coverage and intensity across central and southeast Illinois during the evening of November 30.
Surface temperatures were initially at or below freezing along and west of I-57: however, enough warm air advected in aloft that most of the precipitation began as a mixture of freezing rain and sleet. As the evening went on, surface temperatures continued to slowly climb across east-central and southeast Illinois, with all rain reported in these areas. Further northwest, the icy precipitation continued, resulting in significant ice accumulations along and west of I-55. Many communities from Bloomington southward to Decatur and Springfield reported freezing rain accumulations of one half to one inch, along with sleet accumulations of around one inch. As a result, widespread tree and power line damage occurred, resulting in numerous power outages. Particularly hard hit by ice were the communities of Mt. Pulaski, Decatur, and Taylorville, with severe tree and power line damage (causing power outages lasting at least into December 6). Further west, the precipitation began changing to snow toward midnight across the Illinois River Valley as colder air began to filter in aloft. The snow became heavy after midnight, thanks to impressive large-scale upward motion, as well as an elevated layer of instability. Several locations reported thunder and lightning with the snow and sleet. The icy precipitation along the I-55 corridor eventually changed to snow between 2 and 5 AM, while the rain tapered off further east.
Snow continued to fall until mid to late morning across the western half of the area, with the snow quickly shifting northeastward into northern Illinois. Once the snow came to an end by around midday on December 1, storm total accumulations across the Illinois River Valley generally ranged from 10 to 14 inches, with locally higher amounts.
3 Day Precipitation 7 AM Tue/Nov 28 - 7 AM Fri/Dec 1
Check out coverage of this major winter storm from other National Weather Service offices that cover parts of Illinois.
Northern Illinois (NWS Chicago)
Northwest Illinois (NWS Davenport)
Southwest Illinois (NWS St Louis)
Southern Illinois (NWS Paducah)
Winter Storm photos: