(10:00PM - 2/24/20) A snowstorm continues to look likely to impact the state, Tuesday through Wednesday. This storm system will likely bring widespread accumulating snow to portions of the state during this time period. A drastic shift southward in the expected storm track and associated snowfall totals has been the main story over the past 12-24hrs.
***Synopsis and important disclaimer/information***
As has been the case much of this winter, model guidance has been downright horrible in handling this period, even in the near term. After having a consensus yesterday among model guidance for an axis of several inches of snow across Northern Illinois, model guidance made a uniform giant jump southward today. This significant change in such a short period of time and so close to the event is due in part to the several moving pieces that we discussed in previous updates. How these moving pieces interacted were going to dictate the storm track and strength...and associated location and amounts of snow. Unfortunately, model guidance clearly never had a handle on the overall situation regarding these moving pieces, as they were showing more optimal interaction, and thus a stronger/further north storm system with the axis of snow further north/higher snowfall totals. The significant changes today are fully due to the models mis-handling the interaction of the aforementioned moving pieces, now having far less interaction...leading to a weaker/further south storm system and a snow axis further south/lower snowfall totals.
With this, we now chalk up another event this winter that model guidance heavily struggled with. Unfortunately, model guidance is one of the main factors in creating a forecast, and we have no control of their output. For those that don't know, model guidance is run by government and non-government agencies in several countries across the world. While we at ISC never try to run with exactly what model guidance shows and try to use past experience and knowledge to also aide in forecast development, when the models fail...we generally fail too. That's just how it is in the weather world.
Tuesday morning-Wednesday afternoon...
A mix of rain an snow will develop across Central Illinois Tuesday morning. This activity will fully turn to snow during the afternoon, while also spreading into portions of Northeast and portions of Southern Illinois by Tuesday evening. Snow will then continue across portions of Northeast, much of Central and portions of Southern Illinois through Wednesday morning, before coming to an end. Periods of moderate to even heavy snow will be possible during this time, with high snowfall rates around 1"/hr possible at times.
Final snowfall totals will likely range from 4-7" in the min axis extending into Eastern Illinois, with amounts tapering on either side of this axis.
Below is the snowfall forecast for this event.
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