The term Pneumonia front, first coined by Milwaukee Weather Bureau Office in the 1960s, is used to describe a rare meteorological phenomenon observed on the western Lake Michigan, USA, shoreline during the warm season. These fronts are defined as lake-modified synoptic scale cold fronts that result in one-hour temperature drops of 16 °F (8.9 °C) or greater.
They do not necessarily have to be synoptic, or large scale, cold fronts. Very often in the Spring to early summer the temperature difference between the cold lake waters and the warmer air over land can be as much as 35-40 °F. Under weak prevailing winds, a density current can often develop in the form of a lake breeze that moves from that water to the adjacent shoreline and several miles inland. This "lake-breeze cold front" can drop temperature in places like Chicago, Milwaukee and Green Bay significantly as they cross the area. There has been many a Spring day at Wrigley Field that surprises people who may have travelled from an inland location toward the shore to take in an afternoon game, only to feel the effects of the "pneumonia front" as that cold blast of air comes through.
The following are eighteen occurrences of a lake modified synoptic scale cold front or "pneumonia front".
|June 13, 1909||Michigan City, Indiana|
|May 21, 1938||Will County, Illinois|
|June 6, 1967||Cook County, Illinois|
|June 30, 1975||Lake County, Indiana|
|July 1, 1983||Kenosha County, Wisconsin|
|July 17, 2003||Lake Michigan|
|May 20, 2008 ||Eastern Wisconsin (Lake Michigan)|
|May 21, 2008 ||Eastern Wisconsin (Lake Michigan)|
|May 26, 2008||Cook and Lake Counties, Illinois; Lake and Porter counties, Indiana|
|April 25, 2009 ||Cook and Lake Counties, Illinois|
|June 1, 2009||Cook and Lake Counties, Illinois|
|April 21, 2010||Cook, Lake and Will Counties, Illinois; Lake and Porter Counties, Indiana|
|May 13, 2011||Cook, Lake and Will Counties, Illinois; Lake and Porter Counties, Indiana|
|March 15, 2012 ||Cook and Lake Counties, Illinois; Lake County, Indiana; Milwaukee, Racine and Kenosha Counties, Wisconsin|
|April 13, 2014||Cook, Lake and Will Counties, Illinois; Lake and Porter Counties, Indiana|
|May 27, 2014||Cook, Lake and Dupage Counties, Illinois; Milwaukee, Racine and Kenosha Counties, Wisconsin|
|September 29, 2014 ||Cook, Lake, Dupage and Will Counties, Illinois; Milwaukee, Racine and Kenosha Counties, Wisconsin|
|April 10, 2017||Waukesha, Milwaukee, Racine and Kenosha Counties, Wisconsin|
- Skilling, Tom (May 27, 2008). "WGN Weather Center Blog". Retrieved 2007-05-28.[dead link]
- Adrian, Bart (May 27, 2008). "Bart_Adrian's Blog". Archived from the original on October 11, 2007. Retrieved 2007-05-27.
- "The Impromptu Weather Blog". May 27, 2008. Retrieved 2007-05-27.
- "Did You Feel the Pneumonia Front Last Night?". Archived from the original on September 7, 2008. Retrieved August 2, 2008.
- "It Happened Again Last Night...Another Pneumonia Front!". Archived from the original on May 30, 2008. Retrieved August 2, 2008.
- "Chicago Tribune". April 27, 2009. Retrieved 2009-04-25.[dead link]
- "Another day, another record broken as warm spell shines on". Chicago Tribune. March 15, 2012.
- "FOX6 Weather on Twitter". Twitter. Retrieved 2017-04-11.