Winter storm warning issued. wet snow arrives this evening

Winter Alerts:

Today will be a textbook "calm before the storm" as the weather remains quiet under a cloudy sky. With that being said, today provides a great opportunity to run any pre-storm errands.

Shortly after the evening commute, multiple winter weather alerts will go into effect. Beginning with the WINTER WEATHER ADVISORY, this is for Green, Rock, and Walworth County in S. Wisconsin as well as Winnebago, Boone, McHenry, Ogle, Lee, and Dekalb County in N. Illinois. This will be for the first of two rounds and will run from 8PM/9PM until 6AM Tuesday. Snow moving in overnight will result in slippery travel for Tuesday morning's commute. 

For the second round, Jo-Daviess, Stephenson, Carroll, and Whiteside County will be placed under a WINTER STORM WARNING at 6PM, lasting until 3AM Wednesday morning. 

The portion of the warning for S. Wisconsin has a later start time, starting at 9PM. 

As of this writing, the National Weather Service in Chicago continues to keep a WINTER STORM WATCH in place for Winnebago, Boone, Dekalb, McHenry, Ogle, and Lee County. 

Timing & Impacts:

Low pressure currently over New Mexico will lift to across the Midwest today, landing in the Great Lakes Tuesday evening. Over the weekend, there were hints at a possible northwest wobble in the storm's track, taking it over north central Illinois. 

This would further make the case for the rain/snow mix line to further push into our southeast areas, such as Dekalb and McHenry County. However, forecast models this morning are slightly more in agreement that the low's center will track over I-80 and into the southern tip of the Lake Michigan. This scenario places the highest potential for impacts across northern/northwest Illinois, and southern Wisconsin. Snow associated with round 1 should move in from the south around 8PM/9PM, continuing into daybreak Tuesday. Again, leave extra time for travel as slippery road conditions are likely. 

Widespread snow moves back in shortly before mid-day, lasting through Tuesday afternoon and Tuesday evening. It's during this time in which snowfall rates could be as high as an 1"/hr. 

From mid-day on, road conditions will deteriorate to the point where it could be dangerous to travel. Snow remains likely into Tuesday night, tapering off shortly before the midnight hour.

If you have any travel plans, it may be a good idea to adjust travel plans. With temperatures cooling into the upper 20s, moisture from Tuesday's snowfall will likely freeze, allowing travel impacts to linger into Wednesday morning's commute. 

As previously discussed, there won't be much arctic air to work with, leaving snow to liquid ratios lower than the 10:1 average. This means the snow that falls will be a heavy, wet snow. Great for making snowballs and snowmen, but very sloppy and slushy for travel due to compaction. Sporadic power outages will also be on the table given the nature of the snow along with the fact that strong winds will be present.

How much?

As of this morning, our preliminary snowfall forecast is calling for between 5-9" across most of the region, with isolated higher totals possible. Totals will decrease the closer you get to the rain/snow mix line, which should develop somewhere in between southern Dekalb County and Chicago. 

Now, even though we're a little over 24 hours away from the worst impacts, uncertainties remain. As the storm system approaches, we'll have to monitor both the system's track as well as where the rain/snow mix line develops. Continue to stay updated on the forecast by using the First Warn Weather App as well as tuning in this evening!