What is a "Pneumonia Front" in Weather?

My friend and meteorologist colleague, Dr. Marshall Shepherd recently published an article in FORBES that explains just what is meant by a "Pneumonia Front." Up until now, I've not actually heard of it, and you may not have either... it's about quick drops in temperature. Here's the story. 

(Image: When a cold front moves quickly southward and is enhanced by chilly water temperatures of Lake Michigan, temperatures can rapidly drop near the shoreline.  Credit: National Weather Service))

 

Is Pneumonia Front The New ‘It’ Weather Term? 

Marshall Shepherd, FORBES, May 18, 2023,02:50pm EDT

  I want to preface this discussion with a few points. I have three degrees in meteorology and was the 2013 President of the American Meteorological Society (AMS). I am the director of an atmospheric sciences program at a major university. Yet, before this week, I never heard of the term “pneumonia front.” If the term was unfamiliar to me, there is a good chance it is unfamiliar to you too. Let’s explore whether it is the new “it” term in weather jargon or has more of a legacy than you may think.

I felt compelled to write this short piece because there is already a perception that our weather profession is making up new terms. In March of this year, Grace Toohey tackled the topic for the Los Angeles Times. In her piece, many of us pointed out that terms like Polar Vortex, bomb cyclone, derecho, and atmospheric rivers have been around the field of meteorology for decades. However, social and broader media outlets are using such terms more frequently.

A pneumonia front is a more recently-described phenomenon, but it still dates back further than the media fascination this week. Corey Behnke’s Master’s Thesis (2005) was entitled, “Synoptic and Local Controls of the Lake Michigan Pneumonia Front.” That study was conducted at the University of Wisconsin - Milwaukee. 

(Image: Satellite-indicated stratus clouds associated with a pneumonia front on May 27th, 2008. CIMSS AND SCOTT BACHMEIER) 

In a synopsis of the work found on the University’s website, Behnke notes that pneumonia fronts are defined as, “lake modified synoptic scale cold fronts that result in one-hour temperature drops of 16 degrees F or greater.” 

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SATELLITE ANIMATION VIDEO: The inconvenient convergence of 3 cooling mechanisms across southern Wisconsin: a dense pall of smoke from Canadian wildfires, a southward moving cold front & the inland surge of a lake breeze (aka Pneumonia Front) from Lake Michigan:  https://twitter.com/CIMSS_Satellite/status/1658586614698745856?s=20

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Earlier this week, the National Weather Service - Milwaukee office tweeted the following message about the attention grabbing event:

They offered a more public-facing definition of a “pneumonia front” - a cold front accelerating down Lake Michigan that rapidly drops temperatures as it moves inland. The data below illustrates just how dramatic these events can be. There was a 20 degree temperature drop in 20 minutes. Where I am from, that is an abrupt temperature drop. From poking around, it seems that this is the time of year that such relatively rare event happen.

Scott Bachmeier has an outstanding discussion of these events in a 2008 CIMSS Satellite Blog. He wrote, “Examining surface temperature data from Milwaukee and Madison in Wisconsin, Behnke (2005) documented 25 cases of pneumonia fronts during the period 1948-2003....reduced roughness over the north-south oriented Lake Michigan allowed for stronger impact of the pneumonia fronts over the southern portions of the lake and shoreline, and colder lake temperatures in the north helped to increase the nearshore temperature gradient and frontal propagation.” 

Here’s the bottom line. The term may be new to you and me, but it has been in the meteorological literature for almost two decades.

Note: An embedded hyperlink function was disabled but the link to theMaster’s Thesis work by Corey Behnke can be accessed below:

****************************** Dr. J. Marshall Shepherd, a leading international expert in weather and climate, was the 2013 President of American Meteorological Society (AMS) and is Director of the University of Georgia’s (UGA) Atmospheric Sciences Program.