Arctic air spread into southern Wisconsin behind deep low pressure that tracked to the north of the state.  About 2,000 feet above ground level, 925 mb temperatures fell to -17C to -22C���with 925 mb winds of 20 to 30 knots.  Momentum transfer of these winds to the surface produced gusty northwest winds, which combined with surface temperatures in the single digits below zero to produce wind chills between -20 to -30.  The frigid wind chills began the morning of January 21st across far northern Southeast Wisconsin and most of South-central Wisconsin���then spread across the remainder of southern Wisconsin during the evening of January 21st and continued everywhere into the morning hours of January 22nd.
An interesting side note to this cold outbreak was the fact that it was one of the relatively few times Milwaukee recorded a low temperature below zero without having a snow cover.

Cold/Wind Chill in RACINE, WISCONSIN
From 21-JAN-13 18:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: ASOS

Cold/Wind Chill in KENOSHA, WISCONSIN
From 21-JAN-13 18:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: ASOS

Cold/Wind Chill in MARQUETTE, WISCONSIN
From 21-JAN-13 08:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: COOP Observer

Cold/Wind Chill in GREEN LAKE, WISCONSIN
From 21-JAN-13 08:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: COOP Observer

Cold/Wind Chill in FOND DU LAC, WISCONSIN
From 21-JAN-13 08:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: ASOS

Cold/Wind Chill in SHEBOYGAN, WISCONSIN
From 21-JAN-13 08:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: ASOS

Cold/Wind Chill in SAUK, WISCONSIN
From 21-JAN-13 08:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: AWOS

Cold/Wind Chill in COLUMBIA, WISCONSIN
From 21-JAN-13 08:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: COOP Observer

Cold/Wind Chill in IOWA, WISCONSIN
From 21-JAN-13 08:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: AWOS

Cold/Wind Chill in DANE, WISCONSIN
From 21-JAN-13 08:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: ASOS

Cold/Wind Chill in LAFAYETTE, WISCONSIN
From 21-JAN-13 08:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: COOP Observer

Cold/Wind Chill in GREEN, WISCONSIN
From 21-JAN-13 08:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: AWOS

Cold/Wind Chill in DODGE, WISCONSIN
From 21-JAN-13 18:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: AWOS

Cold/Wind Chill in WASHINGTON, WISCONSIN
From 21-JAN-13 18:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: AWOS

Cold/Wind Chill in OZAUKEE, WISCONSIN
From 21-JAN-13 18:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: COOP Observer

Cold/Wind Chill in JEFFERSON, WISCONSIN
From 21-JAN-13 18:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: AWOS

Cold/Wind Chill in WAUKESHA, WISCONSIN
From 21-JAN-13 18:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: AWOS

Cold/Wind Chill in MILWAUKEE, WISCONSIN
From 21-JAN-13 18:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: ASOS

This event was one of the relatively few times Milwaukee had a low temperature below zero without having a snow cover. Examining the historical climate record back to 1948, which is when regular snow depth records began for Milwaukee, there have been only 17 instances when the low temperature in Milwaukee reached or dipped below 0 ��F with no snow cover on the ground. The most recent occurrence dated back to January 20, 2008 with a low temperature of -6 ��F.

Cold/Wind Chill in ROCK, WISCONSIN
From 21-JAN-13 18:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: AWOS

Cold/Wind Chill in WALWORTH, WISCONSIN
From 21-JAN-13 18:00:00 to 22-JAN-13 12:00:00 (CST-6)
Reported by: AWOS