Will there be a snowstorm in Chicago this week?

The forecast for Chicago for the middle of this week is messy. Rain should develop Wednesday and then transition over to snow Wednesday night into Thursday. Some freezing rain and sleet is possible during the transition but the biggest impact from this system could be the snow it squeezes out on Thursday.

I am rooting for several inches of snow so that my winter forecast verifies. I stuck my neck out on the first day of winter and predicted between 33" to 37". Average snowfall for a winter is 29.6".  So far we have seen 22.4" of snow, just 1.6" below average for the season. It wouldn't take much to bump us over average this week.

There is a lot of uncertainty as to how much snow will fall this week. Models are not in consensus at this point. One way to gauge the amount of uncertainty is to look at an ensemble forecast. The Global Ensemble Forecast System, or GEFS, is a weather forecast model that consists of 21 separate forecasts, or ensemble members. Each of the forecasts is tweaked or perturbed slightly by altering the original observations. The model runs out all the different potential outcomes and the closer those forecasts are to each other, the more confidence is placed in the forecast. Right now, the plumes or various forecasts for the ensemble members range from around an inch of snow to over a foot. In other words, it is still anyone's guess. The mean forecast is for a bit over 5".

The uncertainty is really showcased when looking at two individual models. The GFS, or American model, lays down around 9" to just over 17" of snow across northern Illinois with the heavier end of that range targeting the city.

The ECMWF, or European model, suggests a lot less snow. It lays down abut 1" to 3" for most of the area with 5" or more well south of Chicago and across north central Indiana.

It is too early to make a definitive forecast for snowfall this week. This should serve as more of a heads-up that something is coming Wednesday into Thursday that could have a big impact across the Chicago area. I will be watching closely for many reasons. I am hoping for enough snowfall to push our seasonal total above average so my winter forecast ends up being accurate. If this doesn't materialize, I am running out of time since there is only about two weeks of meteorological winter left.