ASK TOM: Is there a rule between barometric pressure and precipitation?

Dear Tom,
Is there a rule between barometric pressure and precipitation?
– Mark Peterson, Naperville


Dear Mark,
The rule of thumb is: dry with high pressure and wet with low pressure. Low pressure is associated with upward motion that leads to clouds and precipitation, while the sinking motion with high pressure inhibits precipitation.
That being said, Chicago climatologist Frank Wachowski reports that precipitation has occurred with two of the city’s highest barometer readings. Lake-effect snow fell for 14 hours Jan. 26, 1927, with a barometer reading of 30.97 inches. Lake-effect snow fell for five hours Feb. 17, 1989, with pressure at 30.86 inches. Precipitation that occurs with very high pressure normally requires the presence of low-level instability.