Pneumonia front

A pneumonia front is a rare meteorological phenomenon observed in coastal areas of Lake Michigan during spring and early summer. 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.[1] The term was created by the National Weather Service in Milwaukee in the 1960s.[2] While pneumonia fronts occur primarily in the states of Illinois and Wisconsin, pneumonia fronts are also observed in Indiana and Michigan.

Modeled pneumonia front over southeastern Wisconsin, May 16, 2023; see full-size version
map showing motion of pneumonia front of 20–21 May 2008

Pneumonia fronts do not necessarily have to be synoptic, or large scale, cold fronts. They are most common between the months of April to July when the temperature difference between the cold lake waters and the warmer air over land can be as much as 35–40 °F (19–22 °C). 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, Benton Harbor, Green Bay, and Traverse City significantly as they cross the area.

The following are documented occurrences of a lake-modified synoptic scale cold front or a "pneumonia front".

Date Location
June 13, 1909[3] Michigan City, Indiana
May 21, 1938[3] Will County, Illinois
June 6, 1967[3] Cook County, Illinois
June 30, 1975[3] Lake County, Indiana
July 1, 1983[3] Kenosha County, Wisconsin
July 17, 2003 Lake Michigan
May 20, 2008 [4] Eastern Wisconsin (Lake Michigan)
May 21, 2008 [5] Eastern Wisconsin (Lake Michigan)
May 26, 2008[6][3] Cook and Lake Counties, Illinois; Lake and Porter counties, Indiana
April 25, 2009 [7] 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 [8] 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 [9] Cook, Lake, Dupage and Will Counties, Illinois; Milwaukee, Racine and Kenosha Counties, Wisconsin
March 24, 2017[10] Cook, Lake, Dupage and Will Counties, Illinois; Milwaukee, Racine and Kenosha Counties, Wisconsin
April 10, 2017[11] Waukesha, Milwaukee, Racine and Kenosha Counties, Wisconsin
June 1, 2018 Cook County, Illinois; Porter County, Indiana
May 3, 2020[12] Northeast Illinois; Milwaukee, Racine, and Kenosha Counties, Wisconsin
April 27, 2021[13] Cook County, Illinois; Lake, Porter, and LaPorte Counties, Indiana
May 10, 2022[14] Emmet, Charlevoix, Grand Traverse, and Leelanau Counties, Michigan
June 17, 2022[15] Milwaukee County, Wisconsin
April 14, 2023[16] Grand Traverse County, Michigan
May 16, 2023[17] Southeastern Wisconsin, Northeastern Illinois

References
  1. Adrian, Bart (May 27, 2008). "Bart_Adrian's Blog". Archived from the original on October 11, 2007. Retrieved 2007-05-27.
  2. Skilling, Tom (May 27, 2008). "WGN Weather Center Blog". Retrieved 2007-05-28.
  3. "The Impromptu Weather Blog". May 27, 2008. Archived from the original on July 13, 2011. Retrieved 2007-05-27.
  4. "Did You Feel the Pneumonia Front Last Night?". Archived from the original on September 7, 2008. Retrieved August 2, 2008.
  5. "It Happened Again Last Night...Another Pneumonia Front!". Archived from the original on May 30, 2008. Retrieved August 2, 2008.
  6. Bachmeier, Scott (27 May 2008). "Lake Michigan "pneumonia front"". CIMSS Satellite Blog. Retrieved 16 May 2023.
  7. "Chicago Tribune". April 27, 2009. Retrieved 2009-04-25.
  8. "Another day, another record broken as warm spell shines on". Chicago Tribune. March 15, 2012. Archived from the original on March 16, 2012. Retrieved March 16, 2012.
  9. "Brace for the 'pneumonia front:' Skilling says jarring 20-30 degree temp drop to hit tonight". 29 September 2014. Archived from the original on 6 October 2014. Retrieved 30 September 2014.
  10. "March 23-25, 2017: Impressive Day-to-Day Temperature Change, Including a Near-Record Quick Dropdate".
  11. "FOX6 Weather on Twitter". Twitter. Archived from the original on 2017-04-22. Retrieved 2017-04-11.
  12. "US National Weather Service Milwaukee/Sullivan Wisconsin on Facebook". Facebook. Archived from the original on 2022-04-30.
  13. ""Pneumonia Front" comes down Lake Michigan". 28 April 2021. Archived from the original on 1 May 2021. Retrieved 1 May 2021.
  14. "Check this out! After setting a record high of 92 this afternoon, Traverse City dropped 31 degrees in 10 minutes (88 at 6:35pm to 57 at 6:45pm) after a northerly lake breeze pushed through, dramatically cooling the area. #miwx". 10 May 2022. Archived from the original on 11 May 2022. Retrieved 11 May 2022.
  15. "Well MKE did it, at 5:55pm the temp was 82 and by 6:50pm the temp had dropped to 66 resulting in a 16° drop in temps in under an hour. Can officially label this a Pneumonia Front. #wiwx". 17 June 2022. Archived from the original on 18 June 2022. Retrieved 18 June 2022.
  16. "Notice a drastic change in temperature at any point today? Conditions were favorable for the development of lake breezes this afternoon. As a matter of fact, Traverse City fell from a record-breaking high of 86°F at 4:30pm to 61°F by 6:30pm... a 25°F decrease in two hours! #MIwx". 14 April 2023. Archived from the original on 15 April 2023. Retrieved 15 April 2023.
  17. Salgado, Beck Andrew (16 May 2023). "A 'pneumonia front' expected to drop temperatures 20-30 degrees in a matter of minutes on Tuesday". Milwaukee Journal Sentinel. Archived from the original on 16 May 2023. Retrieved 16 May 2023.

Further reading
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