November 30 - December 1, 2006

The first significant storm of the 2006-2007 winter season struck central Illinois on November 30 and December 1.  A wide variety of precipitation was experienced across the region, ranging from rain and thunderstorms…to sleet…to freezing rain…to heavy snow.  The areas hardest hit by wintry precipitation were along and west of I-55, where some locations reported in excess of a foot of snow.

 

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 3).  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 December1, storm total accumulations across the Illinois River Valley generally ranged from 10 to 14 inches, with locally higher amounts.  The highest snow total from the SWOP network came from the town of Henry in Marshall County , where 16 inches fell.  Further east, the snowfall steadily decreased, with totals mainly in the 4 to 6 inch range along I-55 and only one inch or less along I-57.  Most locations along the Illinois-Indiana border and in southeast Illinois saw little or no snow from this system.

SWOP Pictures of the Event


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