Public Information Statement
Issued by NWS Chicago, IL

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NOUS43 KLOT 261659

Public Information Statement
National Weather Service Chicago IL
1159 AM CDT TUE JUL 26 2016 /1259 PM EDT TUE JUL 26 2016/

...Extremely High Dew Points Observed on Sunday...

Dew points are a direct measure of moisture in the air, with
values in the 70s or higher associated with an oppressively humid
air mass. Sunday July 24th brought dew points in the upper 70s to
lower 80s across northern Illinois, which is basically at the
highest end of what can be observed. The setup for these extremely
humid conditions was ideal with a persistent warm air mass able
to hold ample water, southerly winds on Sunday advecting more
moisture into the area, wet ground and even standing water from
recent rains, and evapotranspiration from mature crops.

Here is a look at dew points in Rockford and Chicago and how they
compared to records and climatology:


Rockford (KRFD)

The dew point peaked at 81 degrees at 7 pm on Sunday July 24th.

- A dew point of 81 degrees or higher has only been observed on
22 hourly observations since 1970. The last time was 8 pm on
August 2, 2011.

- There have only been three high dew point episodes (periods of
hours) with values that high since 1970. They were July 13-14
1995, July 29-30 1999, and August 2 2011.

- The highest dew point observed since 1970 was 83 degrees on July
13 1995.


Chicago (KORD)

The dew point peaked at 78 degrees at 1 pm and 5 pm on Sunday
July 24th at Chicago`s official observing site of O`Hare
International Airport.

- The last time a dew point of 78 degrees or higher was observed
was on July 19, 2011. Prior to that was August 1 2002.

- The highest dew point observed in Chicago`s period of record
was 83 degrees on July 30 1999.

As a note, Chicago Midway International Airport had peaked at a
dew point of 79 degrees at 5 and 6 pm on Sunday July 24th. This
was the highest dew point observed at Midway since June 29 2012.


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