Plains, Midwest - Late-summer heat bakes Plains

Summer-like heat will slowly spread east this week as a high-pressure ridge builds in the upper atmosphere. Francine keeps a couple of regions locked in the heat longer.

It's officially Meteorological Autumn, but that doesn't keep Mother Nature from making things toasty. Highs in the 80s and 90s are being found where temperatures are usually in the 60s and 70s this time of year, like in Montana and the Dakotas.

The culprit for this unseasonable warmth is a strong high-pressure ridge churning in the upper atmosphere. At the surface, southwesterly and southerly flow is pumping up the mercury this week. The heat peaks today across the northern High Plains but will shift into the northern and central Plains on Tuesday.

By Wednesday, the heat will barely shift east due to Francine, the newest tropical system churning in the Gulf of Mexico. Its low-pressure circulation will run up against the high-pressure circulation, coming head to head and keeping the warm air mass in place for the northern and central Plains. We hope you didn't close the pools yet!

On Thursday, the air masses budge and the heat spreads to the Midwest and western Ohio Valley. More highs in the upper 80s will be found where many would be expecting to slowly reintroduce sweater weather for this time of year.