Chicago weather in June is pretty nice. Its midwest climate, so it could either be 90 degress, 70 degrees, or raining. Chicago is by the lake, so it gets a little cooler as opposed to the Chicago suburbs.
But it should be decent. Windy is possible... obviously, cause they call us the windy city. Windbreaker should hold you off well unless it rains.
The Hyatt Regency O'Hare is actually in Rosemont, so it's suburban. You won't really have much if any lake-effect cooling there.
According to weather.com's 10-day forecast, they're predicting lower 73 F (23 C) for June 1st (the last day they have available), so unless we get a warm spell after that, I'd say that will probably be about the temperature to expect. You can use zipcode 60656 to check for updates on weather.com.
George A. Roberts IV ~ President & CEO, Purity Networks
Chicago is call the “Windy City” not because it is windy but because of its politics.
During the 1889-1890 bidding for the World's Fair of 1893, Chicago advocates put on a rather long-winded presentation and campaign to win approval. The choice narrowed down to Chicago, New York, Washington and St Louis, and the competition before Congress among these cities was fierce and at times ugly. (The world's fair of 1993, known as the Columbian Exposition, was intended to celebrate the 400th anniversary of Christopher Columbus's landing in America, but was actually held in 1893, a year later than had been planned.)
During the campaign, The New York Sun editor Charles Dana wrote in reference to Chicago's lobbying tactics: "Don't pay attention to the nonsensical claims of that windy city. Its people could not build a world's fair even if they won it." This editorial has been widely credited with popularizing the Windy City nickname.