Streak of 90’s Ends, Cooler Weather to Stick Around

With a high of 87 degrees on Friday, Rockford’s run of 90+ degree weather has come to an end after seven consecutive days. This is the longest such streak in over eight years when temperatures exceeded 90 degrees for 11 consecutive days from June 30 through July 9, 2012. This “cooler” weather will likely stick around through the upcoming week.

The large ridge in the jet stream which sat over the Stateline since the end of June has finally pushed off to the east early Friday. This caused the jet stream to dip just to the south of the Stateline allowing some cooler air aloft to be advected over the area. A fairly deep trough will develop over the Midwest through the weekend causing temperatures to cool into the lower 80’s by Sunday before another ridge starts to build by Monday. Though the jet stream is forecast to remain to the north through most of the week, upper level warm air advection should be fairly tame as no deep ridge persists over the area. The lee side of this ridge that builds in the beginning of the week will drop a large surface high pressure system keeping us dry for Monday and Tuesday. As the mid-level jet dips south by Wednesday, added upward vertical motion and mid-level vorticity brought on by a strong mid-level jet streak situated over the Stateline will aid in bringing some thunderstorm chances to the area for the latter part of the week.