Analyzing the Weather: Northern Illinois Snowstorm. 2/12/25

As the weather shifts across the Pacific Northwest, residents should brace themselves for significant changes during the coming days. Early morning satellite images show a strong mid-level short wave moving southeast. This change will bring a variety of weather conditions, affecting areas from the Four Corners to the Midwest and Great Lakes by Thursday morning. This post analyzes the upcoming weather system, detailing what to expect and how to prepare.

Current Conditions and Progression of the Weather System

The approaching mid-level short wave will travel towards the Four Corners area throughout this evening. As it moves southward, the formation of a low-pressure system will begin, stretching from east Texas to the lower Mississippi Valley by Wednesday morning.

Interestingly, earlier weather models had projected similar trajectories, but this low may be slightly weaker than expected as it heads toward the eastern Great Lakes.

Snowfall Forecast: What to Expect

By early Wednesday morning, light snow is anticipated to cover the region. This forecast is driven by increasing mid-level warmth combined with upper-level divergence that boosts upward motion. Increasing isentropic ascent and rising air due to differential positive vorticity advection (DPVA) should aid in providing a source of "lift" to form precipitation across the area.

Forecast models exhibit differing expectations for snowfall intensity. Some, like the NAM (North American Model), predict a colder scenario, which could result in a mix of snow, sleet, and even freezing rain in southeastern areas. Other Hi-resolution models such as the HRRR, RAP, NAM 3km are coming in with much lesser totals due to some entrainment of dry air in the mid to low levels.

The dynamics associated with the mid-level wave are complicated. The strengthening jet stream is enhancing upper-level divergence, crucial for upward air movement. This typically creates a perfect setting for substantial snowfall, especially in the initial stages as the wave approaches. How fast this wave will deepen and exit the area are key for snowfall accumulations as well. It currently looks as if the surface low will be weaker and moving out quicker than anticipated. The end result looks to be totals around the 2 -5-inch range throughout northern Illinois. There also looks to be a "deformation band" to set up across the area. mainly just north of where the rain/snow/sleet line will be. This can produce snowfall rates of up to 2 inches per hour, causing travel problems during the afternoon and evening commute. This area looks to be just south of the I-80 corridor.

Snowfall intensity is likely to decrease late Wednesday evening, with tapering expected past midnight as the mid-level trough moves out. After this system loses momentum, lower-level winds will shift, bringing in drier air and bringing snow to a halt.

Implications for Residents and Travelers

Heavy snow can reduce visibility, create icy roads, and complicate travel, especially on Wednesday afternoon and evening.

Travelers are advised to stay vigilant by monitoring National Weather Service alerts and exercising caution while driving.

As the situation unfolds, staying informed through local news and weather updates is vital for adapting to changing conditions and potential advisories.

Garrett Nykaza

12Z HRRR Snow Depth forecast. Valid 48 hours out.