Due to recent shifts in the models pulling our area of low pressure further to the South, the prospects for locally heavy snow are on the rise in the Stateline. Winter Storm Watches for our Wisconsin Counties have since been upgraded to Warnings, while Watches have been hoisted for Winnebago, Boone, Ogle, and McHenry Counties effective Friday afternoon into the early evening. I placed a call to the NWS office in the Quad Cities to inquire about the possibility of some sort of advisory for our Western Counties, and the speculation there was that those counties will be added sometime early Friday morning!
The very latest National Weather Service-run NAM model paints a bit of an ominous picture. It takes our area of low pressure from SW Missouri to Champaign to SW Michigan, a very favorable track for heavy snow here! This model generates 0.76" of water to come, which could easily equate to 5-8" of snowfall
The most recent GFS run is staunch agreement with the NAM regarding the track of the system! Such agreement among our models on systems like these is quite rare! Model agreement gives forecasters elevated confidence on the scenario to unfold in the hours leading up to the event! The GFS is a little lower than the NAM as far as precip totals, but would still easily favor a 4"-6" snowfall total in the Rockford Metro!
Given the recent model trends and all the new data coming in, here's our current thinking on how this storm is to evolve. Few light, scattered rain showers will be possible from 3:00 to 9:00, with the changeover to snow commencing quickly thereafter. Areas to the NW will be first to see the change from rain to snow, while areas closer to Chicago will be the last. By 1:00pm, most, if not all of us should be dealing with snow. Snowfall rates between 3:00 and 6:00pm could easily reach one inch per hour! The snow tapers to flurries after 8:00pm. Accumulation forecast as we see now: 4" to 8" from I-88 Northward, with 1" to 4" South of I-88! We'll continue to monitor as the event unfolds!