There haven’t been many days this summer quite like Monday. A reading cooler than Chicago’s 73° official high has occured this season on only four other days since June 1. It was the city’s lowest daytime maximum in nearly two months since June 18, and equalled the area’s normal high on Sept. 17-19. While only five days this summer have failed to break above 73°, last summer’s chill had produced 21 such days by this point in the season.
The cold Canadian air mass also produced lows of 35° in northern Minnesota’s Embarrass and in Osceola in northwest Wisconsin. Frost advisories were in effect overnight in sections of interior Upper Michigan.
Tropical Storm Jose formed west of Mexico’s Yucatan Peninsula over the Bay of Campeche Monday. Its peak winds reached 50 m.p.h., but, the system’s steady westward movement limited its time over the the warm tropical ocean waters curtailing further development.
--Tom Skilling

Taking a cue from this week’s school year start-up in many suburban areas, the season’s first autumnal chill will arrive in Chicago today amidst gusty north winds and a cloud-filled sky. After one of the hottest summers in recent years, light jackets and sweaters will be in order tonight and early Tuesday as temperatures drop into the 50s. With a bit more sun, readings will rebound into the middle 70s Tuesday, and by the end of the week summer will be back in control with the mercury once again pushing the 90º mark.
While the record early season activity in the tropical Atlantic Basin has quieted down, and the area is currently storm free, Japan is bracing for a direct hit from Typhoon Mawar.
Passing near the island of Iwo Jima Sunday night, the typhoon is forecast to make landfall on the central Japan coastline between Osaka and Tokyo on Wednesday with winds as high as 140 m.p.h.

Welcome thunderstorms rolled through the entire rain-starved Chicago area early Saturday, but it was the north side that harvested most of the beneficial rainfall with many areas totaling between one and two inches. Officially, O’Hare measured 1.35 inches of rain, the largest one day rainfall there since last August 28 when 1.41 inches fell. Southern areas were not as fortunate with rainfall tallies sharply tapering off to less than one quarter inch. With drier air now moving into the area, it appears that the rain spigot will be turned off until at least the end of the week.
The next few days also promise to be quite cool having an autumnal-like feel to them, giving the city a preview of rapidly approaching meteorological fall which begins in less than two weeks on September 1. Daytime highs should remain in the 70s Monday and Tuesday, and aided by clear skies and lengthening darkness, overnight lows could approach 50º in the coolest inland suburbs.