SWOP Weekly Weather Discussion

HEADLINE

The upcoming July 4th Holiday looks to be seasonably hot and humid...with storm chances holding off until later in the weekend.

DISCUSSION

A flat west-to-east zonal flow pattern is currently in place across the U.S. This has allowed a cold front to drop through the region and bring a cooler and less humid airmass to central Illinois. Models have been consistently showing an upper-level trough of low pressure coming onshore across the Pacific Northwest...which will create weak downstream ridging over the Midwest by the end of the week. As upper heights rise and the atmosphere modifies, temperatures will gradually warm through the week and will climb into the lower 90s by Friday, July 4th. As the Pacific Northwest wave tracks eastward along the U.S./Canada border, it will eventually flatten the upper ridge and push a cold front southward into Illinois over the weekend. The latest indications suggest the front and its associated rain chances will hold off until late Saturday at the earliest...with the highest rain chances materializing on Sunday, July 6th into Monday, July 7th. After that, the upper ridge will retrograde westward and build over the Desert Southwest. This will set up a northwesterly flow pattern across the Midwest, which will result in slightly cooler temperatures and periodic rain chances next week.

The Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) are currently positive and expected to remain positive over the next week. This generally supports a flat, zonal flow pattern...with no big swings in temperature. As a result, a continuation of near to slightly above normal temperatures looks to continue into mid-July.

The latest 6-10 day outlooks (Jul 7-11) from the Climate Prediction Center (CPC) suggest ABOVE normal temperatures and ABOVE normal precipitation across central Illinois.

Issued: 7/1/25