Ask Tom why: How often has Chicago's barometric pressure dropped below 29.00 inches?

 

Dear Tom

About a year ago, Chicago was hit by a severe storm with record low pressure. How often has Chicago's barometric pressure dropped below 29.00 inches? —Martin Jarebek, Chicago

  Dear Martin,

The Oct. 26, 2010, storm battered Chicago and the Midwest with high winds, severe thunderstorms and some tornadoes. Chicago's official barometric pressure dropped to 29.00 inches, an October record. Chicago climatologist Frank Wachowski noted that barometer readings below 29.00 inches are rare here, occurring in only 18 storms dating back to 1871. March and December have each logged five storms with pressures less than 29.00 inches, followed by January with four and February and April with two each. The city's last low pressure encounter was on Dec. 9, 2009, when the barometric pressure dropped to 28.92 inches. Chicago's all-time lowest pressure was 28.70 inches on March 12, 1923.