National Weather Service United States Department of Commerce

Cold Front Dropping South Across the Western U.S.; Watching Threat for Tornadoes and Flooding in the South

A cold front will push south across the Western U.S. into Tuesday with mountain snow and areas of gusty to high winds. An area of low pressure will form along this front on Tuesday and bring a potential for severe thunderstorms with tornadoes and excessive rainfall in the lower to mid Mississippi River Valley. To the north, heavy snow is possible in parts of the upper Midwest. Read More >

March 23-25, 2017 Day-to-Day Change

Chicago Day-to-Day Temperature Change     Rockford Day-to-Day Temperature Change
Chicago temperature change from March 23-25, 2017     Rockford temperature change from March 23-25, 2017


Near-Record Quick Temperature Drop on March 24

March 24, 2017 brought a sharp late afternoon temperature fall to northeast Illinois and far northwest Indiana. This includes a 20° drop in five minutes near the lake front, and around 30° in just 30-60 minutes! 

The meteorological feature responsible for this was a cold front, but one with strong lake enhancement.  While this marine enhancement to a cold front can happen over the early spring chilled waters of the Great Lakes, to this extreme of magnitude is rare.  These type of cold fronts are sometimes referred to as pneumonia fronts by meteorologists.  These cold fronts tend to progress rapidly southward down the lake and shoreline areas due to the strong density and pressure differences between the air mass behind the front and ambient air mass ahead of it.

Highs and Wind Gusts         Pneumonia Front Forecast
March 24 Observed Highs and Peak Gusts         March 24 Graphical NOWcast of Pneumonia Front


On Friday, March 24, strong southwest winds had steered in near-record to record warm air, with mid-afternoon highs in the lower 80s.  Both Chicago and Rockford had only seen four other years reaching 80°+ this early in the season. Lake Michigan water temperatures on the other hand were in the upper 30s to lower 40s.  As a cold front slowly moved down the lake during the daytime hours (peak heating over land), this thermal contrast set the stage for the surging cold front.

  • For Chicago (O'Hare), the temperature dropped 29° in one hour, dropping from 77° at 5:15 pm to 48° at 6:15 pm.  
    • ‚ÄčThe record dating back to 1872 for largest documented one hour temperature drop in Chicago was 30°, from 71° to 41° from 2 to 3 pm on March 26, 1908.
  • For Waukegan, IL (far northern Chicago metropolitan area), the temperature dropped 20° in just five minutes!  It dropped from 79° at 3:05 pm to 59° at 3:10 pm.  The one hour drop was 31° from 79° to 48°.




ORD Temperature Trace

      ORD Observations
Chicago O'Hare Temperatures       Chicago O'Hare Observations





UGN Temperature Trace

      UGN Observations
Waukegan Temperatures       Waukegan Observations


Other significant temperature drops in Chicago's history include:

  • A fall from 82° to 55° in just ten minutes on April 20, 1936.  The temperature went on to fall to 32° by 4 a.m. on April 21. 
  • Grant Park (not official) - a fall of 22° from 84° to 62° in 2 minutes and 30 seconds on May 9, 1963 due entirely to lake cooling.


NWS Chicago Science & Past Events Page