By Meteorologist Tom Skilling
The cooler temperatures which greet Chicago area residents under gloriously sunny skies Tuesday are but the beginning of a multi-day cool-down which is to take temperatures by Thursday to the chilliest levels since late May.
While Tuesday highs are predicted to be 13-degrees lower than Monday's summer-level 86-degree reading at both O'Hare and Midway, a more potent second push of cool air hits Wednesday afternoon and evening, marked by strengthening northerly winds beneath gathering clouds likely to become showery late in the day. High temperatures, expected to "warm" to the mid-60s midday Wednesday are to pull back to the mid 50s by nightfall and may further dip to the low 40s at normally cooler inland locations by daybreak Thursday.
If Thursday's daytime temperatures conform to current forecasts, it's possible readings won't break above 60-degrees for the first time since late May. A reading THAT cool is an especially good bet if cloudiness is extensive---which it may well be given the steep vertical temperature decline which is predicted by computer models. That's the sort of environment which support cloud formation.
What's remarkable is that cooling of this magnitude is occurring without provoking the development of powerful storms here, like those which swept Upper Michigan late Monday generating 74 mph gusts a Freda and 66 mph gusts at Calumet, Michigan.
It's been 3 weeks since the Chicago's logged an official rainfall of a half inch or more. September's seen only 0.04 inches of rain in its opening 13 days---a paltry tally 1.30 inches below the most recent 30-year average for the period!
An official sub-60-degree high Thursday would be earlier than historic norms; temps that cool didn't occur until October a year ago
An official Thursday high below 60-degrees would be unusual this early in the 3 month meteorological autumn season. Weather records here reveal October 18 has been the date beyond which half or more of days have produced highs of 60-degrees or less.
Chicago's first sub-60-degree high last year waited another two weeks to occur, arriving October 2.
Monday's 86 at O'Hare brings to 53 the number of days at or above 85-degrees; well above the long-term average of 42
Monday's 86-degree high was 10-degrees above normal and marked the 53rd time in 2011 a daytime temperature has peaked at 85-degrees or higher. That tally represents 26 percent more 85+ daytime highs than the long-term average of 42.
Over the term of weather observations which began at O'Hare in 1959, only 8 other years have produced as many or more 85-degree and higher readings by September 13.
Sprawling Canadian high pressure driving the predicted Thursday chill here and threatening upper Midwest and Plains with a freeze
A buckling jet stream helps transport a sprawling early season high pressure into the Chicago area out of Canada's arctic region. In anticipation of its arrival, a freeze watch has been posted for a large section of North Dakota. It's likely advisories for frost and freezing temperatures will be expanded in coming days to include portions of Minnesota and Wisconsin.
Chilliest northwest suburbs could see scattered 30s Thursday morning
While warm Lake Michigan waters and the urban heat island effect---which is the warmth retained and re-radiated at night by the asphalt and concrete in the city as well as the warmth which escapes from buildings---are to temper overnight temperatures a bit in coming nights, far west and northwest suburban areas are likely to see this region's coolest overnight temperatures of the season. Readings there are likely to dip into the 30s for the first time this season.
Southern Plains broiling in triple digits again---new Dallas, Texas record for most 100s to be set Tuesday---but relief in sight
Triple-digits were back in full force across the southern Plains Monday. Dallas/Ft. Worth's record-breaking 103-degree high marked the 69th day of 100-degree and higher temperatures in 2011, tying the 1980 record for the most 100s there.
With 105-degrees predicted Tuesday, that city is headed for the most triple-digit highs recorded in its official 113-year temperature archive there. Relief hits later this week as Canadian air extinguishes the heat.
Temperatures bounce back this weekend
Chicago temperatures bounce back this weekend as southeast winds take hold. By Monday, more southerly winds will import Gulf and Atlantic moisture into the Midwest increasing cloud cover. Prospects of scattered showers and some thunderstorms increase Monday over as much as 30 to 40 percent of the Chicago metro area.
The cooler temperatures which greet Chicago area residents under gloriously sunny skies Tuesday are but the beginning of a multi-day cool-down which is to take temperatures by Thursday to the chilliest levels since late May.
While Tuesday highs are predicted to be 13-degrees lower than Monday's summer-level 86-degree reading at both O'Hare and Midway, a more potent second push of cool air hits Wednesday afternoon and evening, marked by strengthening northerly winds beneath gathering clouds likely to become showery late in the day. High temperatures, expected to "warm" to the mid-60s midday Wednesday are to pull back to the mid 50s by nightfall and may further dip to the low 40s at normally cooler inland locations by daybreak Thursday.
If Thursday's daytime temperatures conform to current forecasts, it's possible readings won't break above 60-degrees for the first time since late May. A reading THAT cool is an especially good bet if cloudiness is extensive---which it may well be given the steep vertical temperature decline which is predicted by computer models. That's the sort of environment which support cloud formation.
What's remarkable is that cooling of this magnitude is occurring without provoking the development of powerful storms here, like those which swept Upper Michigan late Monday generating 74 mph gusts a Freda and 66 mph gusts at Calumet, Michigan.
It's been 3 weeks since the Chicago's logged an official rainfall of a half inch or more. September's seen only 0.04 inches of rain in its opening 13 days---a paltry tally 1.30 inches below the most recent 30-year average for the period!
An official sub-60-degree high Thursday would be earlier than historic norms; temps that cool didn't occur until October a year ago
An official Thursday high below 60-degrees would be unusual this early in the 3 month meteorological autumn season. Weather records here reveal October 18 has been the date beyond which half or more of days have produced highs of 60-degrees or less.
Chicago's first sub-60-degree high last year waited another two weeks to occur, arriving October 2.
Monday's 86 at O'Hare brings to 53 the number of days at or above 85-degrees; well above the long-term average of 42
Monday's 86-degree high was 10-degrees above normal and marked the 53rd time in 2011 a daytime temperature has peaked at 85-degrees or higher. That tally represents 26 percent more 85+ daytime highs than the long-term average of 42.
Over the term of weather observations which began at O'Hare in 1959, only 8 other years have produced as many or more 85-degree and higher readings by September 13.
Sprawling Canadian high pressure driving the predicted Thursday chill here and threatening upper Midwest and Plains with a freeze
A buckling jet stream helps transport a sprawling early season high pressure into the Chicago area out of Canada's arctic region. In anticipation of its arrival, a freeze watch has been posted for a large section of North Dakota. It's likely advisories for frost and freezing temperatures will be expanded in coming days to include portions of Minnesota and Wisconsin.
Chilliest northwest suburbs could see scattered 30s Thursday morning
While warm Lake Michigan waters and the urban heat island effect---which is the warmth retained and re-radiated at night by the asphalt and concrete in the city as well as the warmth which escapes from buildings---are to temper overnight temperatures a bit in coming nights, far west and northwest suburban areas are likely to see this region's coolest overnight temperatures of the season. Readings there are likely to dip into the 30s for the first time this season.
Southern Plains broiling in triple digits again---new Dallas, Texas record for most 100s to be set Tuesday---but relief in sight
Triple-digits were back in full force across the southern Plains Monday. Dallas/Ft. Worth's record-breaking 103-degree high marked the 69th day of 100-degree and higher temperatures in 2011, tying the 1980 record for the most 100s there.
With 105-degrees predicted Tuesday, that city is headed for the most triple-digit highs recorded in its official 113-year temperature archive there. Relief hits later this week as Canadian air extinguishes the heat.
Temperatures bounce back this weekend
Chicago temperatures bounce back this weekend as southeast winds take hold. By Monday, more southerly winds will import Gulf and Atlantic moisture into the Midwest increasing cloud cover. Prospects of scattered showers and some thunderstorms increase Monday over as much as 30 to 40 percent of the Chicago metro area.
