Snow moves in Tuesday afternoon, impacting the Tuesday evening and Wednesday morning commute

Winter Storm Warnings and Winter Weather Advisories have been issued for all of northern Illinois and southern Wisconsin, beginning as early as Tuesday afternoon for some and lasting through Wednesday morning. Snow is expected to move in first Tuesday mid to late afternoon, lasting through the evening before briefly mixing with sleet and then freezing rain during the overnight. Precipitation will likely change over to rain around sunrise Wednesday.

High pressure moving into the Midwest Monday helped to clear skies for most in the Stateline and warmed temperatures into the low 30s. That high also brought in some fairly dry air which will help keep our skies mostly clear through early Tuesday morning. Our next storm system, however, will be quick to roll in from the southwest Tuesday afternoon with an area of low pressure lifting up from the central Plains Tuesday afternoon, into northeast Iowa and northwest Illinois late Tuesday night.  

The cold, dry air in place following the departing high pressure system from Monday will work to keep the first half of Tuesday dry. Moisture is expected to rapidly increase, however, which could cause snow to fall as early as 3pm - especially for areas west and southwest of Rockford. As the atmosphere continues to saturate, the snow will continue to spread through the rest of the Stateline during the evening, becoming a bit more heavy after 6pm. The moderate to heavy snow will reduce visibility for a time, possibly down to half a mile, and quickly accumulate on the roads. The reduced visibility and accumulating snow will have an impact on the evening commute Tuesday.

As the low pressure system moves closer to Iowa it'll draw up more warm air as winds in the lowest level of the atmosphere increase. This will cause a brief window of sleet, but most likely freezing rain as we near Midnight and early Wednesday morning. Ice accumulations up to a tenth of an inch are possible, but higher amounts are also possible further south of Rockford where the temperature may reach 32 degrees a little earlier, and for longer. The snow could linger for a time near the Wisconsin/Illinois border.  

The heaviest precipitation will begin to taper off around sunrise Wednesday as temperatures warm near/above freezing. Most of the precipitation will then come to an end by Wednesday afternoon. Snowfall amounts across a good portion of the area will likely range from 4-8 inches, with the higher amounts confined to northwest Illinois and southern Wisconsin. The amount of snow will depend on how quickly temperatures warm Tuesday night. A quicker arrival of warm air means less snow lasting into Tuesday night. If the warmer air is delayed a bit, then the snow could linger a little longer. Exact amounts of both snow and ice will likely change within the next 12-18 hours as the storm system nears. However, the impacts will still be there most likely for the Tuesday evening commute, and possibly Wednesday morning commute. The greatest impacts to the roads will take place between 6pm Tuesday and 6am/7am Wednesday.