Saturday, October 6, 2012

Chicago Marathon Weather

Weather condition for the Chicago Marathon and current upper air flow

Credits:

Chicago Tribune

It will be chilly for the 2012 Chicago Marathon. Early morning temperatures for the start of the race will be from 33-38 degrees. The warmest will be along the lake front. By early afternoon temperatures will have climbed to around 50. Early morning winds will be northwest 4-8 mph, highest near the lake. By early afternoon the winds will be northwest 10-15 mph. Skies will be mostly sunny to add a warming feel if you are in the sunshine. That is where you want to be if you are a spectator.
The graphic from the Chicago Tribune gives a pretty good picture of conditions during the race. Interesting to note how warm 4 of the recent 5 events have been. Of course, the worst conditions were those in 2007. What made those conditions so bad was not the heat itself, but the moisture (dew point) level of the air. The higher the dew point, the higher the moisture, and the less the body can be cooled down as the perspiration does not evaporate. It is the evaporative process that produces the cooling. Moist days feel sticky because your skin moisture is not evaporating as quickly as on dry air days.
The morning low temperature is not going to drop any lower than the dew point. On the other 80+ days, the lows were in the upper 40s to low 50s. This means dew points have to be that low or lower. Dew points that low signify dry air. The low in 2007 was only 67. Dew points that day were in the mid 60s which is quite humid air. Running in the humid air over heated many runners, causing the marathon to be cut short. Water ran out fairly quickly along the race route. Quite a number of runners were taken to the hospital due to the heat and humidity combination.
While it will be chilly for the runners, it will be even colder in the suburbs of Chicago. The graphic shows the reason for the cold air, an upper level flow coming down from northwest Canada. Morning lows for this Saturday morning away from the lake and city heat were all around freezing, with upper 20s over northwest Illinois. Sunday morning will find lows a few degrees cooler than this morning. Lows for Sunday morning will drop into the upper 20s in those areas away from the city heat and the lake, with mid 20s in northwest Illinois.
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Allan Fisher, Chicago Weather Examiner

A retired meteorologist (32 years) from the National Weather Service. Career ranged from a regular shift meteorologist to a Meteorologist In Charge of a weather unit in the FAA air route traffic control centers. Forecast experience ranging from every day public forecasts to issuing severe storm...