Peoria, Ill. (WMBD) — A strong storm will move across Central Illinois Thursday night and Friday bringing heavy precipitation and strong winds to the area. While confidence is high that an impactful, very wet, storm system will move across the region, confidence in how much of that falls as snow and accumulates is much lower.

The track of the system has shifted a but further south in the last 24 hours and it appears the area of low pressure will end up passing through southern Illinois. Typically, this would be a favorable track to bring heavy snow to Central Illinois but there are a lot of factors working against this with this system…

  • Low snow ratios
  • Limited supply of cold air
  • Surface temperatures near to above freezing
  • Warm ground temperatures
  • Snow mainly falling during the day
  • Higher Sun Angle

There are ways for these factors to be overcome and one way is for the storm to produce tremendous rates of heavy wet snow Friday morning, heavy enough to offset any melting that would occur. However, given the limited supply of cold air already in place, the storm will have to generate it’s own through a process called dynamic cooling. This occurs when a storm strengthens and generates a lot of rising air. As the air rises it expands, cools and condenses ultimately lowering the temperature of the surround environment allowing rain to change to snow.

Storm Timing

Rain is expected to spread across Central Illinois between 12 am and 3 am Friday with heavier rain moving towards I-74 around sunrise. Between 6 am and noon, rain should begin to change to snow for some along and west of the Illinois River the eat of the Illinois River between 10 am and 3 pm. Exactly when this change over occurs will have a significant impact on eventual snow accumulations. A change over later in the day would make it harder for snow to accumulate as the ground would be warmer.

Snowfall Probability Forecast

Due to all the issues stated above, confidence in snowfall amounts remains much lower than what is typically seen at this range. It is a true boom or bust forecast that could result in several inches of snow or nothing at depending on temperatures. That said, here’s a first attempt snowfall forecast that will likely need to be adjusted on Thursday.

The slideshow below shows the European Ensemble probabilities for various amounts of snow. It’s important to note that this particular model assumes a 10:1 snow ratio which is likely too high, so the the percentages displayed are likely a bit too high. That said, it does paint a decent picture as to where the heaviest snow is mostly likely to fall.

Precipitation Forecast

Most of Central Illinois is expected to receive 1-2 inches of rain. The heaviest rain will fall along and east of I-55 where localized amounts over 2 inches will be possible.