Does it rain or snow more often on Friday or Saturday or Sunday than on the other days of the week?

Dear Tom,

Does it rain or snow more often on Friday or Saturday or Sunday than on the other days of the week? It seems like that. I’m wondering if there is a seven-day cycle that makes weekend weather worse.

Devon Cox,
Lombard

Dear Devon,

A seven-day cycle of precipitation does not exist in Chicago’s climate. Nor does precipitation occur more frequently on any given day of the week. A scan of Chicago’s precipitation records shows that measurable precipitation (0.01 inch or more) falls on either 33 or 34 percent of all days of the week: Sun 33%, Mon 33%, Tue 34%, Wed 33%, Thu 33%, Fri 34%, Sat 33%.

A bad experience with weekend weather can dominate our remembrance of past events. A weekend picnic washout, for example, will be remembered more than a similar event that comes off without a hitch.