SWOP Weekly Weather Discussion

HEADLINE

After a couple more mild days, a significant pattern shift will signal much colder weather through at least the end of next week.

DISCUSSION

A flat west-to-east zonal flow pattern will allow a Pacific-origin airmass to push into central Illinois over the next couple of days. As a result, temperatures will climb into the lower to middle 50s by Tuesday, January 13th. Meanwhile a short-wave trough currently coming onshore across northern British Columbia will crest the Rockies, then dive southward by the middle and end of the week. This feature will carve a significant upper trough southward to the Gulf Coast and send a strong cold front through central Illinois on Wednesday. The front will be accompanied by strong N/NW winds and a few rain and snow showers...followed by much colder highs only in the 20s on Thursday. After that, additional short-wave energy dropping southward out of Canada will re-enforce the prevailing deep upper trough east of the Rockies. This will set the stage for an extended period of cold conditions from Saturday, January 17th through at least the following week. While no major storm systems are expected to impact the region, scattered snow showers accompanying the waves will likely lead to a light snow accumulation by the weekend.

The Eastern Pacific Oscillation (EPO) is currently in a positive phase, but is projected to become strongly negative...then remain negative through the end of next week. This suggests a continuation of the western CONUS ridge/eastern CONUS trough pattern through the period, which spells much below normal temperatures for central Illinois. After that, the EPO trends back into weakly positive territory...perhaps leading to a reprieve from the cold by the last week of January.

The latest 6-10 day outlooks (Jan 17-21) from the Climate Prediction Center (CPC) suggest BELOW normal temperatures and BELOW normal precipitation across central Illinois.

Issued: 1/12/26