Winter Storm Warnings issued ahead of next winter storm

A Winter Storm Warning has been issued for all of northern Illinois and southern Wisconsin beginning either late Thursday night or early Friday morning, lasting through Noon Saturday. Snow is expected to move in overnight Thursday, impacting the Friday morning commute. Heavier bursts of snow are possible during this time with snow accumulations of a couple inches likely. It may be a good idea to plan for a little extra time to get where you need to go Friday morning.

Temperatures have fallen into the teens in some locations Thursday evening where the skies are clear. This has caused some shallow ground fog to develop, especially in some of the open and rural areas. Temperatures will remain in the teens and 20s through the evening but are expected to rise close to 30 degrees by sunrise Friday. 

Snow moves in after Midnight from the south, overspreading much of the area by 2-4am Friday.

Temperatures initially as the snow falls will remain below freezing, so any snow that comes down during that time will stick to surfaces. This could cause some issues for the Friday morning commute. As temperatures continue to warm the transition from a lighter snow to heavier snow will occur through mid-morning. Increasing winds from the northeast will reduce visibility as the snow falls. Snow and slush covered roads are also possible around sunrise Friday.

The rain/snow line is still a big question mark with this system and just how far north it gets into northern Illinois Friday. Right now, it looks like it reaches the I-88 corridor, but it could lift a little further north of that through early afternoon. If it does, more locations will see a rain/snow mix - or just plain rain - into the afternoon Friday. This would help reduce overall snow totals where the mix occurs. Just north of the rain/snow line, however, periods of heavier snow remain possible. This threat looks to be highest north of the state line, as well as to the northwest (northwest Illinois and northeast/eastern Iowa).

As the low moves closer to northern Illinois and continues to strengthen, colder air wrapping in will transition over whatever mix we had earlier in the day to all snow. This process should take place after 4pm - if not a little sooner. The intensity of the snow may not be as high, but the winds will be increasing through Friday evening and night, gusting as high as 45 mph. Colder air moving in after 9pm will help to transition over whatever snow that does come down to a lighter and fluffy snow. Strong winds will continue into Saturday morning with difficult travel conditions remaining.

The uncertainty with the rain/snow and milder temperatures during the day Friday does raise some questions with just how much snow will accumulate. But it's important to remember that the impacts of this system will outweigh the snow totals. Friday morning periods of heavy snow and reduced visibility will cause travel difficulties. By Friday evening and overnight an increasing wind will cause whatever snow that is still falling to blow around and will lead to some drifting in open and rural locations. Temperatures will fall through the day Saturday, with wind chills in the single digits all afternoon, falling below zero around sunset.