In one of the most dramatic and stunning meteorological about-faces I've seen in my nearly 20 year career, we've gone from being the precipice of digging out from our most significant snow system of the winter to now wondering if there'll even be enough to shovel!
For much of the day Sunday, there was a good amount of agreement among several computer models in the development of a winter storm system which appeared likely to produce a significant amount of accumulating snow, easily the most significant of the season. With the storm still being two days out, though, we knew the potential for things to change was still there, and that nothing was yet set in stone.
Beginning late Sunday Night, and continuing through the day Monday, it was becoming dramatically more clear with every model run that this was not going to be nearly the event as originally advertised. There are two distinct reasons for this. First, earlier on, the models were suggesting this system was going to be the combination of two individual storm systems that would merge, or phase, into one large system. When phasing occurs, you tend to get a much stronger, more dynamic, more energetic storm with an abundant supply of moisture. It became clear by Monday Morning that the storms would not phase, and we'd be left with two much weaker systems. Still, that did not eliminate the chances for snow in the Stateline. Snow still appeared a good bet, and quite likely even enough to shovel, but the prospects for a huge snowstorm were no longer there.
Additionally, we always have to keep a very close eye on the track, or the path, the storm systems take. Even the most subtle shift in the track of the storm can have major ramifications on the forecast. A shift of 50 to 100 miles can often be the difference between getting a ton of snow and getting next to nothing. That is exactly why we refrain from posting accumulation graphics until we're within 24 to 36 hours of the storm. Too often we see graphics posted and shared on social media that have extremely inflated accumulation numbers several days before the storm arrives. Almost every time, these posts and images go viral, and almost every time, they are wrong. This is one of those times.
Computer model forecasts began a subtle southerly shift between the 6pm runs Sunday Night and the Midnight runs Monday Morning. This shift still put us in the crosshairs for the heaviest snow, but the shift southward was underway. Between the Midnight runs and the 6am runs Monday Morning, an even more significant shift to the south occurred, shifting the heaviest snow much farther south, and showing a much weaker system due to the lack of phasing. Come Noon Monday, another nudge to the south took place, so much so that it began to advertise parts of the Stateline picking up no snow at all. So between 6:00pm Sunday Night and Noon Monday, we went from a potentially crippling storm to minimal snowfall. That's how important it is for us to closely monitor the storm track, and to be responsible when it comes to posting snow accumulation maps. It has long been our policy to avoid hyping up storm systems. It's far more important for our forecast to be right than it is to be the first one out there.
With that said, our revised forecast is as follows, given the latest trends. There will be a good part of the area that sees no snowfall accumulation whatsoever. Those will be areas north and west of Rockford. In the Rockford Metro, and most spots south of US-20, expect a half inch to one inch, especially Tuesday Night into early Wednesday Morning. One or two locations south of I-88 and east of I-39 may pick up 2 to 3 inches of wet snow. Gusty winds will create the potential for blowing and drifting snow as well.