This warm weather pattern is due to a strong summer-like ridge of high pressure blocking any cooler fall-like air masses from surging southeast into the Great Lakes and eastern half of the country.
By mid-week; a stronger jet core is progged to evolve into the trough as another upper low drops into the trough in the vicinity of North Dakota (above). As the system advances east, this is slated to push into the Lakes Region (below). Of course, this is days away but a notable change from this week.
Enjoy the several days of summer-like weather as indications are for more typical fall-like weather near the close of the month. However, this won't be the last of the above normal or warm weather as extended patterns indicate variable fluctuations in the prevailing jet stream early October.
Next we'll take that look back at the rather mediocre summer - in a few ways.
Making weather fun while we all learn,
Bill Deedler - SEMI_WeatherHistorian