A classic strong autumn cold front progressed through the entire Midwest by Thursday Night. Here is a look at a surface weather map from 4 pm Thursday afternoon with temperatures as an image. The front clearly stands out, highlighted not only by a temperature gradient but an abrupt shift in the wind from south to west northwest!
The cold front which plowed across the area during the afternoon and early evening hours of Thursday, October 25th dropped temperatures 20 degrees or more in less than 2 hours! From afternoon temperatures in the low-mid 70s, readings slid into the 40s by mid-evening. Here is a graphic which shows the temperature (red curve) and dew point (green) at O'Hare and Rockford. Note the sharp drop toward the right side of each graph - the passage of the cold front is easy to see! Below that is a text listing of temperature drops experienced across the area.
PUBLIC INFORMATION STATEMENT NATIONAL WEATHER SERVICE CHICAGO IL 917 AM CDT FRI OCT 26 2012 /1017 AM EDT FRI OCT 26 2012/ ...DRASTIC TEMPERATURE DROP EXPERIENCED ON THURSDAY... A POWERFUL AUTUMN COLD FRONT MOVED ACROSS NORTHERN ILLINOIS BETWEEN 3 AND 630 PM AND THROUGH NORTHWEST INDIANA BETWEEN 630 AND 800 PM ON OCTOBER 25TH. WITH STRONG SOUTHERLY WINDS AHEAD OF THE FRONT AND SOME SUNSHINE DURING THE DAY...TEMPERATURES HAD WARMED INTO THE MID TO UPPER 70S. THE COLD FRONT BROUGHT TEMPERATURES RAPIDLY DOWN INTO THE 40S...INCLUDING A 22 DEGREE DROP IN ONE HOUR AT GARY. BELOW IS A LISTING OF THE MAXIMUM TEMPERATURE DECREASES BETWEEN THE TOP OF THE HOUR OBSERVATIONS AT AREA SITES DURING THIS EVENT. NOTE THAT EVEN MORE SIGNIFICANT DROPS MAY HAVE OCCURRED BETWEEN THE HOURLY OBSERVATIONS. LOCATION TWO-HOUR TEMPERATURE DROP FOUR-HOUR TEMPERATURE DROP ----------------------------------------------------------------- AURORA -21F -29F CHICAGO DUPAGE -23F -29F CHICAGO MIDWAY -22F -28F CHICAGO OHARE -20F -28F DEKALB -22F -28F GARY -23F -29F JOLIET -23F -29F KANKAKEE -25F -28F MORRIS -24F -29F PERU -20F -29F PONTIAC -23F -29F RENSSELAER -20F -26F ROCHELLE -21F -27F ROCKFORD -20F -27F ROMEOVILLE -23F -29F VALPARAISO -19F -27F WAUKEGAN -20F -29F $$ MTF