Mark Johnson's forecast: September starts autumn ups and downs

CLEVELAND - Summer heat and humidity will hang on through the Labor Day weekend.

And then, BAM. Right on cue. The cool arrives.

September is a fickle month, and we are likely to experience some of that up-and-down weather this year.

The current weather pattern has a large ridge of high pressure over the Central Plains and Mississippi Valley. Under that dome of high pressure is some pretty intense heat. Thermometers from Iowa to Texas are reaching up into the 90s to near 100 degrees. Some of that heat has spun off into the lower Great Lakes and northern Ohio this past week. 

But, the high pressure ridge is expected to shift farther west this weekend into the Four Corners region. This will allow two cold fronts to drop into Ohio from the north next week. The first one arrives Monday morning. Refreshingly cool air will follow for Tuesday (highs in the 60s). The second front will bring a reinforcing shot of mild in on Thursday.

In the graphic below, blue means cooler than normal. Notice temperatures across much of northern Ohio should average below normal for the first seven days of September. Average highs are in the upper 70s.

For the second week of the month, it's a battle between summer and some cooler fall-like air. So, the net result (graphic below) from Sept. 6 thru Sept. 16 will be temperatures within a degree either side of normal.

The chillier air returns for the third week of the month, as shown below, as leaves really start to turn colors. Highs in the 60s during the day. Lows in the 40s and 50s over night. Temperatures will likely average a degree or 3 below normal through much of the eastern 2/3rds of the US.

The BOTTOM LINE: September temperatures will likely average near to slightly BELOW normal. As for rainfall, precipitation forecasts suggest average to slightly BELOW normal rainfall for Ohio for the month of September.

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