We’ve already had a lot of snow this season. What is the most snow we’ve ever had for March and April combined in any one season?
— Robert Schickel, Chicago
Despite the start of meteorological spring March 1, Chicago’s snow season typically doesn’t end until early April. March has hosted two of the city’s 10 heaviest snowstorms, led by a massive 22.3-inch snowfall March 25 to 26, 1930, as measured at Midway Airport. The year with the most combined March-April snowfall was 1926, when the two-month total was 29.7 inches. At least some snow fell on 18 days in March, including a storm delivering 12.6 inches at month’s end. A 6.1-inch snowstorm that followed quickly April 2 to 3 boosted the city’s accumulated snow cover to a season-high depth of 10 inches.
You sometimes mention Chicago’s “continental climate.” Just what is that?
Meg Klyn, Chicago
A continental climate is the climate that is characteristic of the interior of a landmass of continental size. It is marked by large annual, daily and day-to-day ranges of temperature. Relative humidity tends to be low and precipitation is irregular and is moderate or light. The annual extremes of temperature occur about a month after solstices (usually December 21 and June 21).
In most respects, a continental climate is the opposite of a “marine climate,” a climate dominated by the ocean and characterized by high humidity and small seasonal and day-to-day temperature variations. Strictly speaking, Chicago experiences a modified continental climate due to proximity to Lake Michigan.
When was the last time we had below-zero temps in the month of March in Chicago?
— Debbie, Streator
Subzero readings in March are rare in Chicago, having occurred on only 15 days in 11 Marches dating to 1871. Chicago climatologist Frank Wachowski scoured the record books and has these details:
It’s been a dozen years since the last March subzero, a low of minus 7 on March 4, 2002. Before that, the city logged lows of minus 1 on March 8, 1982, and March 2, 1980. March 1943 hosted three subzero lows, the most of any March — with a minus 3 on March 3, minus 2 on March 7 and minus 7 on March 8. The month’s all-time lowest temperature was a frigid 12 below zero on March 4, 1873. Wachowski noted that the city registered its latest-in-the-season subzero day on March 22, 1888, when the low fell to minus 1.
If my memory is right, the temperature of snow stays at about 31 or 32 degrees. Is this correct?
— Scott, Marseilles, Ill.
It is incorrect. Like any solid substance, the temperature of snow will rise or fall depending upon the temperature of its environment. (Of course, snow will melt when exposed to above-freezing temperatures.) If snow — say, a snowball — were placed in a freezer with a temperature of minus 5 degrees, the snowball would cool down to that temperature.
On clear, calm nights, the surface of a field of snow will radiate heat and cool several degrees below the temperature of the overlying air. This is the same process that causes frost to form on grass even though the air temperature immediately above may be a few degrees above freezing: The grass radiates heat.
I am curious what Chicago’s longest stretch of hours at or below zero is. Ours here in Lincoln, Neb., is 188 hours in December 1983, including a lovely high of 10 below zero on Christmas Eve.
— Eric Hunt, Lincoln, Neb.
The late-December 1983 outbreak of polar air that you are referring to was widespread. It covered virtually all of the U.S. east of the Rockies. And, like Lincoln, that’s when Chicago recorded its longest span of temperatures continuously at or below zero degrees.
Beginning at 7 a.m. Dec. 22, 1983, and continuing through Christmas Day to 11 a.m. on Dec. 26, Chicago’s temperature remained at or below zero for 100 consecutive hours, the longest frigid spell in the city’s history. Chicago’s high/low temperatures on Christmas Eve were -11/-25 degrees, respectively.
Where are the world’s wettest and driest places?
— Scottie Mackay
The world’s wettest spot is on Mount Waialeale on the island of Kauai, Hawaii, with annual precipitation of 471.68 inches. Prevailing trade winds force warm, moisture-laden tropical air up the mountain slopes and torrents of rain pour out.
The driest location is Arica, Chile, on the Pacific coast of South America, about 1,200 miles south of the Equator. Based on a 43-year period, average annual precipitation is 0.02 inches. Prevailing winds there are from the east, and the Chilean coast lies in the rain shadow of the Andes. Also, cool stable air sits offshore and it resists any attempt by atmospheric motions to transport it upslope.
By comparison, Chicago’s average annual precipitation is 36.89 inches.
Which Chicago winter has produced the most days where temperatures fell below zero? Where does this winter fit into that mix?
— James West and Ciatto Munhane
Dear James and Ciatto,
The city’s last subzero reading, 5 below on Feb. 12, raised Chicago’s number of below-zero days this winter to 22, the most since the winter of 1981-82, which also logged 22 days. The only winters with more were 1884-85, with 25, followed by 1935-36 and 1962-63, both with 24. While Chicago has dropped below zero as late as March 22 (minus 1 in 1888), the frequency of below-zero occurrences drops off sharply after mid-February. However, a late-season surge of arctic air expected to hit later this week is likely to add more days to this season’s total, threatening to approach or equal the city’s all-time 1884-85 record.
A family member believes tornadoes can form in snowstorms. Is this a myth?
— Sarah Shakespeare, Mendota, Ill.
Tornado researcher and Chicago native Brian Smith said that in his 30-year career he can’t recall a tornado occurring during a snowstorm. He said, “Even with Chicago’s thundersnow event during the February 2011 blizzard, instability that produced those thunderstorms was elevated, occurring several thousand feet up. To have a tornado, you must have instability originating near the surface, meaning warm air at the surface and very cold air aloft. That is very hard to do in the winter. The opposite prevails during a snowstorm: It’s colder at the ground and warmer aloft. This prevents parcels of air from rising, a requirement for tornado formation.”
Unusually warm water in the North Pacific Ocean is indirectly responsible for our cold winter. I believe underwater volcanoes in the Pacific “Ring of Fire” are responsible for the warm water. What do you think?
R. Fairchild, Waukegan
Dr. Reinhard Flick of the Scripps Institution of Oceanography in San Diego says it’s unlikely that underwater volcanoes are involved. The volume of water in the North Pacific Ocean, much of which is greater than 10,000 feet in depth, is huge. The heat necessary to warm that volume of water from underneath would be correspondingly immense. Presumably, such a prolific source of heat would not be difficult to locate. Also, the presently abnormally warm ocean waters involve only the surface layer (the upper few hundred feet), not water at depth.
What is the average date of the end of Chicago’s snow season?
— Brian Chapman, Chicago
After our long and snowy winter, that date can’t arrive too soon for many Chicagoans. Typically the city receives its last measurable snowfall around April 3 and the last flurries a few weeks later around April 21, but those are only average dates. The city’s measurable snow season has actually ended twice in February, on Feb. 27, 1997, and Feb. 28, 1994, with only flurries following. However, the city also has recorded measurable snowfall in May in nine seasons — most recently half an inch on May 6, 1989. The city’s latest measurable snowfall was 0.2 inches on May 11, 1966, and its latest trace of snow on June 2, 1910.