Has Chicago ever gone through March and April without a 70-degree day?

Dear Tom,
With our first 70-degree day in sight, have we ever gone through March and April without getting one?

William J. Ooms Jr.
Dear William,
It has happened only once, and that was in 1874 when the city did not see its first 70-degree day until May 7. In those days the official temperature site was downtown near Lake Michigan where the typical arrival date for the season’s first 70 is April 9. Inland areas usually record their first 70 about March 25. Despite the late arrival of spring warmth, the summer of 1874 did go on to produce some hot weather. There were 17 days in the 90s, the two hottest being a 99-degree high July 6 and a 98 on July 25. There were no extended heat waves that summer, but the city did record three straight 90s, Aug. 19 to 21.

Tornado season has been calm so far

Illinois’ first thunderstorms of spring usually arrive in March, but it has been relatively tranquil in the Chicago area in recent weeks. This has masked a climatological fact: March is the beginning of the Illinois tornado season. In fact, the worst tornado disaster in the United States — the Tri-State Tornado of March 18, 1925, was primarily an Illinois event. Of the 695 deaths in Missouri, Illinois and Indiana from the tornado, 606 of them were in Illinois.

Changes ahead
A major weather pattern change is under way, the result of which will be sharply colder temperatures across the western United States next week and much warmer readings in the Great Plains and Midwest. Temperature contrasts such as those fuel strong thunderstorms and will increase the risk of severe weather in the Plains by midweek.
– By Richard Koeneman, WGN Weather Center Meteorologist

Relative humidity below 10 percent

Dear Tom,
Does the relative humidity ever go below 10 percent anywhere?

–Sara McPhail

Dear Sara,
Occurrences of very low relative humidity are rare and are confined almost exclusively to deserts. Chicago’s relative humidity has never dropped below 10 percent, and its all-time low humidity value is 13 percent, measured on three occasions: May 10, 1934; April 11, 1956; and April 8, 1971. The world’s lowest relative humidity value seems to be 2 percent and has been recorded at several U.S. locations — all desert locations — such as Las Vegas; Phoenix and Yuma, Ariz.; and Death Valley, Calif. Worldwide, readings of 2 percent have been recorded in the Sahara and have assuredly occurred in other desert regions around the world, though data are sparse from those areas.

Climb from the chill about to begin

Spring, far more than any other season, is noted for its variable and turbulent weather characterized more often than not by huge temperature swings. Chicago is about to experience a dramatic example of that as a major weather pattern change occurs during the next seven days. During that period. the city’s temperatures are forecast to surge more than 50 degrees from Friday morning’s low in the lower 20s to afternoon readings in the middle 70s by Thursday. Chicago last experienced 70-degree warmth on Nov. 8 (71 degrees).
 
About winter

Chicago’s lowest temperature this past winter was 1 degree below zero (Jan. 3) and that was the city’s only subzero day. On average, the city experiences seven subzero days during its cold season.