All-time record high dewpoint recently set at Springfield

Extremely muggy conditions invaded much of central and southeast Illinois on Monday, August 4th.  The dewpoint temperature is commonly used in meteorology to describe atmospheric moisture.  It is the temperature to which air must be cooled in order to reach saturation (assuming air pressure and moisture content are constant).  In general terms, the higher the dewpoint, the more oppressively humid the air feels.  Dewpoints often reach into the low and mid 70s over the eastern half of the U.S. in summertime.

A rare set of factors may have combined on August 4th to produce widespread dewpoints in the upper 70s and lower 80s across central and southeast Illinois.  Much above normal rainfall so far this year has led to abundant soil moisture.  This has helped local vegetation which usually peaks in evapotranspiration (moisture loss) from mid July to early August.  In addition, a warm front established itself across northern Illinois on the afternoon and evening of the 4th.  This allowed southerly winds to supply moisture-rich air to the region.  Other small-scale effects and local factors may have played a role in producing extremely high dewpoint readings.

Springfield IL established a new dewpoint record of 83 degrees F at 6:52 PM on the 4th.  This broke the old record of 82 degrees from August 19, 1993 at 5 PM.  The period of hourly records at Springfield dates back to 1948.

Here are the peak dewpoints from around the area during the afternoon and evening of August 4:

Location           Dewpoint      Time (cdt)
Springfield         83                   1852-1952
Bloomington      81                   1556-1956
Decatur              81                   1554-1654
Lincoln                81                   1825-1945
Galesburg          81                   1345-2245
Lacon                 81                   1645-1725
Peoria                80                    1854-2254
Champaign        79                   1453-1553
Jacksonville       79                    1505-0045
Taylorville           79                    1505-1725
Mattoon              78                    1453-1553


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