It is already cool for the season and temperatures will cool even more today and for the next several days.
The upper air flow determines the general temperature pattern. During the summer, it is typical for a ridge of high pressure to park over the western U.S. and occasionally shift eastward over our heads. The ridge makes it warm to hot if it is overhead. Example: Phoenix had a high of 119° yesterday.
Starting this weekend and into much of the upcoming week, a trough of low pressure will be slowing moving over the central U.S. Upper level troughs generally bring cooler weather. Example: a very abnormal cut-off low brought snow to the Ozarks in early May!
We will have this weak upper level low over our heads for the next few days and it will keep things on the cool side of normal through the end of the week. Cool will mean highs in the seventies and lows in the fifties for the next few days.
Even when temperature do creep back up by the end of the week, I don’t see any nineties on our future for the next seven days.
What might happen is an occasional bout of showers or even some thunder. This happen yesterday mainly east of Springfield and might happen again today. This showers activity is connected with small disturbances which will be rotating around the upper level low this week.