Peoria, Ill. (WMBD) – A complex storm system moved through Central Illinois Tuesday and Wednesday producing snow accumulations of 2-4 inches over much of Central Illinois. While a quick burst of snow moved through the region Tuesday morning, resulting in accumulations up to 1 inch south of I-74, the bulk of the snow came Tuesday night and Wednesday morning.
Here are the latest reports. Additional reports will be added as they come in.
Peoria – 3.8″
Hanna City – 3.5″
Peoria – 3.5″ (NWS Official Storm Total Tuesday & Wednesday)
Mclean – 3.0″
Canton – 3.0″
Chatsworth – 3.0″
Arrowsmith – 2.9″
Henry – 2.9″
Morton – 2.8″
NW Peoria – 2.8″
Chenoa – 2.4″
Normal – 2.3″
Streator – 2.1″
Eureka – 2.0″
Avon – 2.0″
Lincoln – 1.9″
El Paso – 1.9″
Washington – 1.9″
Galesburg – 1.9″
This was one of the most complicated forecast in recent memory. For several days, models had the bulk of the snow in Iowa and Wisconsin where projections of 8-12 inches were looking likely. On Sunday, the models started to shift the axis of heavier snow further southeast, a trend that would continue through Tuesday. In the end, the main axis of snow was displaced to the southeast by 250 miles.
So what happened? Why did the models and forecast struggle to handle this system?
There’s not one particular reason for the poor performance with this system, but likely a combination of things.
Bad model data
In order for models to generate a forecast they need a starting point. So conditions from the day before are fed into the models and a forecast is calculated out from there. The models did not pick up on the unseasonably warm temperatures we had over the weekend which gave the models a bad starting point. Having errors from the get go only leads to bigger errors down the road.
Poor observing over the pacific northwest
The United States has a vast network of observation sites which help paint a complete picture of what’s going on now. Unfortunately, the network of observations across British Columbia and over the Northern Rockies is not as vast. This contributes to holes in the analysis which is then filled in by model extrapolation…more errors.
A complex setup
This wasn’t a case of the storm just moving south. Instead, it’s that the storm didn’t develop in the way it was advertised in the days leading up to the event. This system involved the merger of two separate storms, a process called phasing. This process is very complex and can be rather difficult for models handle. However, given how all numerical model guidance was pointing to a significant snow event across northern Illinois, Iowa and Wisconsin, there was very little reason to believe the models were struggling.
There were signs of a southeastern shift in the storm track on Sunday. I made a post noting this shift on Sunday morning on my Facebook page.
By Monday morning, all model guidance suggested that the main axis of heavier snow would run through central and northeastern Illinois with the heaviest snow focused east of the Illinois River. While several models produced snow accumulations of 6-10 inches in the area, my official forecast called for a widespread 4-7 inches with pockets of 5-8 inches knowing that the wet snow would melt and compact under its weight.
Here is the official forecast that was made Monday afternoon. It should be noted that several phone apps had Central Illinois receiving 8-12 inches of snow at this time.
New model data would come in throughout the evening and there were signs that the models were continuing to shift the track of heavier snow to the southeast. At 8:49 PM on Monday I wrote this post on Facebook discussing how the evening model runs were showing signs of further shifts in the storm track and that snow accumulations may have to be significantly reduced. However, since I did not have a complete set of updated model data to analyze, I didn’t want to adjust the forecast based on an incomplete data set. So, I went on air at 9 and 10 pm with the same forecast from earlier, but I did mention how I may need to cut the forecast in half by the end of the evening.
The latest models were in by 11:30 pm and I officially cut snowfall totals in half across Central Illinois with the forecast published to our website at 12 am Tuesday. Instead of a widespread 4-7 inches, Central Illinois would see 2-4 inches with locally higher amounts east of I-39. This would be my “final call” forecast before the storm arrived and was fairly accurate. Unfortunately, this was a late adjustment and most people wouldn’t see it until it was too late. You can see that forecast below…
By Tuesday evening, the projected storm total snowfall amounts didn’t change but the forecast was narrowed down to what we could expect from Tuesday evening through Wednesday morning. Additional snowfall amounts of 1-3 inches were expected west of the Illinois River with 2-4 inches east of the Illinois River. Some of these projections were a little low along I-80 and across Knox County but they were on target elsewhere. You can see the Tuesday night snowfall forecast below.
In the end, the final call forecast was mostly accurate with most of Central Illinois seeing 2-4 inches of snow. Amounts were a little less than expected east of I-39, but between the snow Tuesday morning and Tuesday night, most of these areas saw around 3 to 4 inches of snow.