As the weather warms this spring, we will begin to have extended periods with above-freezing temperatures. What is the longest period the city has gone without dropping to 32 degrees or lower?
— John Hastings, Niles
Chicago’s growing season — the period between the last freeze in spring and the first freeze in autumn —typically runs about six months, from mid-April to mid- or late October. In 1931, however, the last spring freeze was April 2 and the first autumn freeze was delayed until Nov. 24, a record 236 days later. The exceptionally late autumnal freeze was a direct result of the location of the city’s official thermometer on the University of Chicago campus, near the mild water of Lake Michigan. At Midway Airport, the first 32-degree fall reading occurred more than three weeks earlier, on Nov. 1.
I have heard reports of pieces of ice weighing 50 pounds falling from the sky. Is that possible?
— Jim Hembree
The term “megacryometers” was coined about 12 years ago to describe huge conglomerations of ice that on rare occasions fall from cloudless skies. Generally weighing between 2 and 150 pounds, but sometimes 400 pounds, megacryometers have been the subject of considerable study in recent years, but their cause and formation is unknown.
Hailstones form, and are kept aloft, in the rising air currents of thunderstorms. But the atmospheric conditions when megacryometers occur — clear skies and immensely powerful updrafts whose strength is far beyond what is believed possible — are a mystery. Chemical analyses of megacryometer ice have ruled out aircraft origins.
I remember a winter in the late 1980s that produced only about 40 inches of snow, but most of it came in three of four big storms. Did any winters during that period match my memory?
Gary Ryan, Bartlett
You are remembering the winter of 1987-88 that brought the city 42.6 inches of snow for the entire season, yet produced three major snowstorms that accounted for more than 60 percent of the total seasonal snowfall. The first storm occurred on December 14-15, delivering 9.1 inches of snow. Just two weeks later, a second storm brought 8.0 inches on December 28. January snowfall was lackluster with just 5.4 inches for the month, much of it falling in a series of light snows from January 22-26. February hosted the season’s third major snowstorm, a 9.4 inch affair spanning February 9-11.
Which day of the year in Chicago has the greatest range between its record high and record low?
— Mark Gloudeman, Yorkville
The date is Jan. 20 with a remarkable temperature span of 90 degrees between its record low of 27 degrees below zero in 1985 and 63-degree record high in 1906.
A close runner-up is Dec. 24 with a range of 89 degrees between its record high of 64 degree in 1889 and record low of 25 below zero on a frigid Christmas Eve in 1983.
If this record is ever to be broken, March 4 appears to be a good candidate. With a frigid 12-below record low (1873) and a record high of 73 degrees (1983) already on the books for an 85-degree span, a reasonably reachable high of 79 degrees would elevate this date into the top spot.
Has a tornado has ever hit the same spot twice?
Definitely, yes. Weather phenomena do not “remember” past events and therefore do not avoid repetitious occurrences. Thelma Holt can testify to that. Her house, located in Moore, Okla., a south suburb of Oklahoma City, experienced not two but three direct strikes from tornadoes in less than five years: on Oct. 4, 1998, on May 3, 1999, and May 8, 2003. The first two tornadoes caused repairable damage but the third tornado destroyed the structure.
The likelihood that a tornado will strike a particular spot in the United States is greatest in the Central and South Great Plains, but estimates of strike frequency vary greatly, ranging from once in 400 years to once every 4,000 years for a powerful tornado.
Despite this winter’s cold and snow, it seems like it was sunnier. Am I correct?— Ben Walsh
Your perception is correct. Chicago climatologist Frank Wachowski reports that this winter was sunnier than normal, delivering 47 percent of its possible sunshine, compared with the 43 percent winter normal. February was exceptionally sunny, logging 60 percent of possible sun, well above the month’s 47 percent average. It was the city’s sunniest February since 2006, which also averaged 60 percent. December was winter’s cloudiest month with just 39 percent of possible sun compared with the 41 percent norm. January had a 43 percent average, slightly above the 42 percent normal. The city basked in its sunniest winter nearly a century ago in 1916-17 when it received 59.1 percent of its possible sunshine.
What is Chicago’s longest string of sub-freezing high temps in March?
— Anna P., Wilmette
Chicago’s normal high temperatures are on the rise in March, climbing from 40 degrees on March 1 to 53 degrees by the end of the month. But the arrival of spring warmth in the city is often delayed, and the month has logged its share of chilly weather. March 1960, the city’s coldest, opened very chilly, logging subfreezing temperatures on 17 days, including a record 14-day string from March 1-14.
During the two-week cold snap, high temperatures remained in the 20s on 10 days, the chilliest back-to-back highs of 21 on March 4-5.
Nights were also frigid, and though no subzero temperatures were recorded, overnight lows bottomed out in the single digits on four occasions.
With the subzero low on March 3, Chicago has logged below-zero temperatures in four consecutive months. How often has that happened?
— Kent Rhodes, Lisle
With the help of Chicago climatologist Frank Wachowski we checked the record books and found that the city has logged subzero temperatures in four consecutive months in just six cold seasons dating back to 1870-71.
Prior to this season, the most recent was in 1981-82, when the 22 subzero days spanned Dec. 20-March 8.
While researching this data, Wachowski discovered that in two of those six seasons subzero weather actually covered five months: In 1872-73 the 19 subzero days ran from Nov. 29-March 4, and in 1887-88 there were 21 below-zero days from Nov. 29-March 22, the city’s latest subzero on record.
What can you tell us about long ago Chicago TV weatherman P.J. Hoff?
— Dave Gavin, Mt. Prospect
P.J. Hoff was an iconic Chicago weatherman on WBBM-Ch. 2 in the 1950s and ’60s. His forecasts were presented on a large U.S. map on which he would place hand-drawn symbols of sun, clouds, rain and snow and high- and low-pressure systems.
He had a host of regular cartoon characters, including Achoo to give the pollen count and the Vice President in charge of Looking Out the Window and Mr. Yell ’n’ Cuss to deliver the forecast and current weather conditions. Hoff would often write down the temperature and then turn it into a cartoon that would relate to the current weather or an upcoming holiday.
He retired in 1968 to St. Simons, Ga., where he lived until his death in 1981.
How does one convert from millibars to inches of mercury?
It’s possible to measure air pressure in several units, including inches of mercury, millibars and hectopascals, but meteorologists prefer to use millibars. One millibar (mb) equals about 0.03 inches of mercury, and a convenient reference point is 1000 mb, which is equivalent to 29.53 inches. An easy conversion from millibars to inches of mercury is to start at the 1000 mb/29.53 inches reference point and add or subtract .03 inch for every millibar the pressure reading differs from 1000. For example, a hurricane whose central pressure is 915 mb differs by 85 mb and yields 26.98 inches. A bitterly cold arctic high pressure system with a central pressure of 1050 mb is equivalent to 31.03 inches of mercury.