The cool summer of 2009 is poised to deliver another round of below normal, May-level daytime readings Friday and Saturday.
Thursday's predicted 82-degree high may be the last 80-degree reading likely to occur in the Chicago area until Tuesday. With extensive cloudiness expected to accompany the abnormally cool incoming air mass, readings will be hard-pressed to break above 70 degrees. Temperatures at such levels this time of the year are truly rare--81 years of weather observations at Midway Airport show only six instances in which back-to-back highs in late July have been as cool as the 68-degree and 70-degree highs predicted for Friday and Saturday. A buckling jet stream is behind the predicted cool-down. Northwest winds stacked vertically from the ground tens of thousands of feet aloft assure the flood of cool air from Canada will be hard to stop.
Widespread cloudiness and the fact that Midwest days are nine hours shorter than those in the Arctic this time of year are among the factors helping southbound air masses to grow cooler as they sink into our area.
Thursday's predicted 82-degree high may be the last 80-degree reading likely to occur in the Chicago area until Tuesday. With extensive cloudiness expected to accompany the abnormally cool incoming air mass, readings will be hard-pressed to break above 70 degrees. Temperatures at such levels this time of the year are truly rare--81 years of weather observations at Midway Airport show only six instances in which back-to-back highs in late July have been as cool as the 68-degree and 70-degree highs predicted for Friday and Saturday. A buckling jet stream is behind the predicted cool-down. Northwest winds stacked vertically from the ground tens of thousands of feet aloft assure the flood of cool air from Canada will be hard to stop.
Widespread cloudiness and the fact that Midwest days are nine hours shorter than those in the Arctic this time of year are among the factors helping southbound air masses to grow cooler as they sink into our area.
