Peak Observed Heat Index Values

A late summer heat wave has gripped central Illinois for the past couple of days, thanks to a large upper-level ridge of high pressure that has developed over the region.  Several clusters of thunderstorms have occurred along the northern periphery of the ridge, providing locally heavy rainfall and temporary relief from the heat to locations along and north of the I-74 corridor.  Elsewhere around the area, hot and very humid conditions have been the rule.  High temperatures on Saturday, August 23rd ranged from the middle 80s across rain-cooled areas near I-74 to the lower 90s further southwest.  As the ridge strengthened, highs were even hotter on Sunday, with readings ranging from the upper 80s along and east of I-57 to the middle 90s in the Illinois River Valley.  Both days featured extremely high dewpoint temperatures in the upper 70s to around 80 degrees.  Due to the hot and very humid conditions, afternoon heat index values climbed well above the 100 degree mark.  Here is a look at some of the peak heat index readings observed over the weekend:

Saturday, August 23                                                                           Sunday, August 24

Location Temperature Dewpoint Peak Heat Index   Location Temperature Dewpoint Peak Heat Index
Peoria 84 77 94   Peoria 93 78 109
Springfield 92 79 109   Springfield 95 78 111
Champaign 88 78 102   Champaign 88 79 103
Decatur 89 80 106   Decatur 92 78 107
Bloomington 84 77 94   Bloomington 90 79 106
Mattoon 89 79 104   Mattoon 88 78 102
Lawrenceville 92 80 110   Lawrenceville 89 77 102

NOTE: The above table shows the highest temperature/dewpoint combination observed on hourly data from automated stations at several central Illinois airports.  Slightly higher heat index values may have been achieved between these observations.  In addition, local effects such as proximity to crops and water sources may lead to higher heat index readings on your home weather stations.      

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