Well the storm system that we have been talking about for several days now is ongoing early this morning across portions of the state with a narrow band of moderate to heavy snow that has already dropped a few inches of the white stuff from portions of western Illinois up into the suburbs of the Chicago metro area. South of this narrow band of heavy snow, rain is the dominant precipitation type (with a small zone of a mix) given surface temperatures are warmer the further south you go. This is just the beginning and I'll dig into the latest and what's to come the next 36 hours or so.....
Our main upper level low that will be responsible for the second round of accumulating snow across portions of the area tomorrow is still well back to our west and southwest this morning, located over Colorado. It will continue out into the plains later today and eventually come ENE into the Midwest tonight and into tomorrow morning.
To start, the loop below runs from 1am earlier this morning all the way till 9pm tomorrow night. As you can see, the model did pretty well with the narrow band of heavy snow right now and over the next few hours that led to a swath of a few inches so far this morning. Going forward, not much has really changed to the forecast with mostly rain and/or a break in the action expected this afternoon and this evening across much of the area as surface temperatures warm well into the 30's. As we get into tomorrow (Halloween), again....not much has changed so expect rain to flip back to snow from west to east across northern and central Illinois during the early to late morning hours. Once it flips, expect at least a several hour period of accumulating snow with some areas (northern Illinois favored) seeing several hour inches of snow from late morning to early evening tomorrow.
Regarding the exact forecast for trick or treaters for the kids on Thursday afternoon and evening. All we have to say is don't shoot the messenger.....as its going to be some of the worst Halloween/trick or treating weather that most of us have seen around this area, especially across the northern half of the state or so. Not only will it still be snowing during the late afternoon and early evening hours, but temperatures will be continuing to drop and range from the upper 20's to low 30's by 5 or 6pm (5pm shown below). Lastly...to go along with those temperatures and falling snow, winds will be quite gusty with sustained winds of 10-20mph with gusts up to or even exceeding 30mph.
Our latest thinking on expected snowfall totals is shown below as we continue to expect this to be a record breaking and historical Halloween snowstorm and one none of us might never see again this time of year.