Feb 24th-26th Significant Snow Accumulations Expected As Winter Storm Arrives Overnight Tonight Into Tomorrow

Some differences and details remain with this forecast which is to be expected when forecasting winter weather but confidence does continue to increase and for that reason, our expected snowfall totals are shown below. The potential is there for this to be quite the winter storm and one that could produce the heaviest snowfall totals of any system this winter...

Our initial two systems are now board over the U.S. this morning with the southern stream upper level low exiting the southern plains and moving into the Midwest this afternoon and evening. This will bring mostly rain to the state today and a chance of snow across northern Illinois later tonight. The more important, northern stream wave is moving through Montana and Wyoming this morning and will be crossing the Rockies and ejecting out into the plains tomorrow night into Tuesday morning. It is what happens after this that is still in question and making the models differ some. 

The trend has been for a slower trailing wave (coming down from Montana and Wyoming) and a faster/weaker initial wave coming through the Midwest today. This in turn leads to less phasing of the two systems and a weaker system overall...at least initially. The other thing and trend to watch is a third wave shown below valid on Wednesday at noon on this particular model, digging southeast out of southern Canada. Some model guidance attempts to then phase the second main system that enters the plains and eventually our area with the Canadian wave. Yes, this is all a bit tricky but the take away here is more phasing usually equals a stronger storm and therefore probably more snow. 

This winter storm continues to look like it will unfold how it is shown in the below animation, running from noon today to 6am on Wednesday. 

1. Rain will overspread much of the state this morning into the afternoon hours, continuing into the evening for some and mostly falling as light rain. There could be a narrow swath of accumulating snow late tomorrow night across portions of northern Illinois with light accumulations possible.

2. By mid-late Tuesday morning, expect a filling in of more widespread snow from portions of western Illinois on northeast into northern Illinois and the Chicago metro area. This will then continue into and through the evening and overnight hours, most likely impacting the evening rush hour in some fashion. Surface temperatures will be right around or just below freezing though so main roadways and interstates could remain more wet than snow covered but we will fine tune those details as we get closer. 

3. As the upper level low gradually strengthens overhead or near the area, snowfall continue to develop/pivot over northern and central Illinois through the mid-late morning hours on Wednesday, before waning in intensity from west to east by Wednesday afternoon. The potential is there for some impressive snowfall rates Tuesday night through Wednesday morning nearing or exceeding 1"/hr along with a chance of thundersnow which would only mean heavier snowfall rates. 

Below is our first expected totals map across the state and as you can see, we are expecting significant snow accumulations across the northern portion of the state. 

​MP