Pneumonia front

Modeled pneumonia front over southeastern Wisconsin, May 16, 2023; see full-size version

Map showing motion of the pneumonia front of May 20–21, 2008.

A pneumonia front, also known as a lake-modified synoptic scale cold front, is a rare meteorological phenomenon observed in coastal areas of Lake Michigan, in the United States, most commonly between the months of April to July. The phenomenon, according to the National Weather Service, consists of a cold front that accelerates southerly down Lake Michigan, rapidly dropping temperatures in coastal areas of the lake by 16 °F (8.9 °C) or greater.^[1][2] These fronts are often followed by fog clouds, and, less commonly, rain.

Pneumonia fronts are most often observed when there is a large temperature difference between the cold lake waters and the warmer air over land, sometimes as much as 35–40 °F (19–22 °C). These conditions are present in spring and early summer. 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.

Pneumonia fronts occur most frequently on Lake Michigan's southwestern shore, in cities such as Chicago, Milwaukee, and Kenosha. However, they are also commonly observed elsewhere on the lakeshore, including cities such as Michigan City, Benton Harbor, Green Bay, and Traverse City.

History

The first documented pneumonia front was on June 13, 1909, in Michigan City, Indiana.^[3][4] The term 'pneumonia front' was coined by the National Weather Service in Milwaukee in the 1960s.^[5]

Causes

Pneumonia fronts occur when a cold front (generally of synoptic scale), typically approaching from the north or northeast, encounters a mass of cold, dense air that has persisted over Lake Michigan, typically a remnant of winter conditions. The air mass fuels the cold front, allowing it to grow in density and momentum as it travels south along the lake. This movement displaces the warmer, less dense air over land, leading to an abrupt and significant temperature drop.^[6] Lake Michigan's elongated north-south shape and two long north-south bays (Green Bay and Grand Traverse Bay) allow for pneumonia fronts to pick up great speed and change air temperatures relatively far inland.

Documented occurrences

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

Date	Location
June 13, 1909[4]	Michigan City, Indiana
May 21, 1938[4]	Will County, Illinois
June 6, 1967[4]	Cook County, Illinois
June 30, 1975[4]	Lake County, Indiana
July 1, 1983[4]	Kenosha County, Wisconsin
July 17, 2003	Lake Michigan
May 20, 2008 [7]	Eastern Wisconsin (Lake Michigan)
May 21, 2008 [8]	Eastern Wisconsin (Lake Michigan)
May 26, 2008[9][4]	Cook and Lake Counties, Illinois; Lake and Porter counties, Indiana
April 25, 2009 [10]	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 [11]	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 [12]	Cook, Lake, Dupage and Will Counties, Illinois; Milwaukee, Racine and Kenosha Counties, Wisconsin
March 24, 2017[13]	Cook, Lake, Dupage and Will Counties, Illinois; Milwaukee, Racine and Kenosha Counties, Wisconsin
April 10, 2017[14]	Waukesha, Milwaukee, Racine and Kenosha Counties, Wisconsin
June 1, 2018	Cook County, Illinois; Porter County, Indiana
May 3, 2020[15]	Northeast Illinois; Milwaukee, Racine, and Kenosha Counties, Wisconsin
April 27, 2021[16]	Cook County, Illinois; Lake, Porter, and LaPorte Counties, Indiana
May 10, 2022[17]	Emmet, Charlevoix, Grand Traverse, and Leelanau Counties, Michigan
June 17, 2022[18]	Milwaukee County, Wisconsin
April 14, 2023[19]	Grand Traverse County, Michigan
May 16, 2023[20]	Southeastern Wisconsin, Northeastern Illinois

See also

• Bomb cyclone
• Cold front
• Hurricane Huron
• Lake-effect snow
• November gale
• Pneumonia

References

1. Shepherd, Marshall. "Is Pneumonia Front The New 'It' Weather Term?". Forbes. Retrieved August 14, 2024.
2. Adrian, Bart (May 27, 2008). "Bart_Adrian's Blog". Archived from the original on October 11, 2007. Retrieved May 27, 2007.
3. "REAL or FAKE?: The 'pneumonia' front". News 5 Cleveland WEWS. May 17, 2023. Retrieved December 21, 2023.
4. "The Impromptu Weather Blog". May 27, 2008. Archived from the original on July 13, 2011. Retrieved May 27, 2007.
5. Skilling, Tom (May 27, 2008). "WGN Weather Center Blog". Retrieved May 28, 2007.^{[dead link‍]}
6. Tarlach, Gemma (June 2, 2021). "Pneumonia Fronts Are Mysterious, 'Drastic' Weather Events". Atlas Obscura. Retrieved August 15, 2024.
7. "Did You Feel the Pneumonia Front Last Night?". Archived from the original on September 7, 2008. Retrieved August 2, 2008.
8. "It Happened Again Last Night...Another Pneumonia Front!". Archived from the original on May 30, 2008. Retrieved August 2, 2008.
9. Bachmeier, Scott (May 27, 2008). "Lake Michigan "pneumonia front"". CIMSS Satellite Blog. Retrieved May 16, 2023.
10. "Chicago Tribune". April 27, 2009. Retrieved April 25, 2009.^{[dead link‍]}
11. "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.
12. "Brace for the 'pneumonia front:' Skilling says jarring 20-30 degree temp drop to hit tonight". September 29, 2014. Archived from the original on October 6, 2014. Retrieved September 30, 2014.
13. "March 23-25, 2017: Impressive Day-to-Day Temperature Change, Including a Near-Record Quick Dropdate".
14. "FOX6 Weather on Twitter". Twitter. Archived from the original on April 22, 2017. Retrieved April 11, 2017.
15. "US National Weather Service Milwaukee/Sullivan Wisconsin on Facebook". Facebook. Archived from the original on April 30, 2022.^{[user-generated source]}
16. ""Pneumonia Front" comes down Lake Michigan". April 28, 2021. Archived from the original on May 1, 2021. Retrieved May 1, 2021.
17. "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". May 10, 2022. Archived from the original on May 11, 2022. Retrieved May 11, 2022.
18. "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". June 17, 2022. Archived from the original on June 18, 2022. Retrieved June 18, 2022.
19. "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". April 14, 2023. Archived from the original on April 15, 2023. Retrieved April 15, 2023.
20. Salgado, Beck Andrew (May 16, 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 May 16, 2023. Retrieved May 16, 2023.

Further reading

• "Synoptic and Local Controls of the Lake Michigan Pneumonia Front", Cory Behnke, M.S. Thesis, University of Wisconsin - Milwaukee (2005)