As high pressure moves east, winds will swing around to southwest and strengthen Saturday — flowing up the backside of the departing high pressure. Early morning temperatures will start out quite cool — in the upper 30s at cold-prone locations away from the lake and city. By afternoon, sunny skies will combine with the warming winds to allow temperatures to rebound back into the middle and even upper 60s at a few locations.
Sunday, a strong 125 mph jet stream will flow across southern Canada, enabling gusty southwest winds to bring warmth in from the Mississippi Valley. Chicago temperatures will top out close to 80 degrees Sunday afternoon. Runners will experience ideal mid-50s temperatures at the start of the Chicago Marathon, but quickly warming temperatures along with the strong buffeting winds will create real challenges later in the morning into the afternoon.
A cold front will approach from the northwest Sunday night, with a chance of a few brief, light showers along the frontal boundary as it moves through the Chicago area early Monday. Temperatures will even off about midday and then slowly fall as cooler high pressure follows into northern Illinois. Fair skies, gusty northwest winds and lower temperatures can be expected at the Chicago Cubs-St. Louis Cardinals National League Divisional Series game.