We are continuing to keep a close eye on the evolving winter storm that looks to be affecting a large portion of the Midwest this weekend, including here in Illinois, beginning on Friday night and continuing through the day on Saturday. Even though we are continuing to get closer to this event, several questions still remain with how this exactly plays out for us here across the state.
What we continue to know: A storm system will originate out of the southern plains and move through what currently looks like the Ohio River Valley Friday night through Saturday afternoon, with a swath of snow on the north side. Confidence is growing on there being two areas of higher snowfall totals with the first being across northern Illinois from a narrow band of heavier snow Friday night. The second area of heavier snow would be further downstate associated with the surface low itself during the day on Saturday.
What we don't know: Given the system is still out over the Pacific Ocean, we still do not know the exact track and strength of both the upper level low and eventual surface low that will form and move through the southern plains. These tracks are very important with regard the placement of accumulating snow certain portions of Illinois.
Our system is still forecast to come ashore the West Coast tomorrow evening and cross the Rockies Friday morning. It is the exact track of this that remains uncertain and what is continuing to give model guidance fits.
Also, it will be dependent on the amount of phasing we see from both the wave moving into the southern plains and the wave digging south and southeast across southern Canada at the end of the loop below. The more these two separate waves come together, the better chance at a more significant and major winter storm. Less phasing would lead to a weaker system moving through this weekend.
We continue to be confident in an impressive area of snow to move into northern Illinois Friday night and Saturday morning, possibly dropping several inches of snow as shown in the loop below. What happens after Saturday morning remains to be seen. Some model guidance is more bullish on several inches of snow across central Illinois late Friday night into Saturday morning. If the area of low pressure tracks further north, than that snow on Saturday afternoon would be further northwest across Illinois and continue well into the afternoon hours.
Below is a mean snowfall forecast for this system, which currently shows the heaviest swath across the heart of state. This is based off an average of 16 ensemble forecasts and will likely change over the next few days as we get closer. Outside of this swath, across northern and southern Illinois, there will likely be several inches of snow and we could also see the heaviest swath shift either north or south, depending on the track of the surface low. Stay tuned for continued updates as well as our first snowfall map.