Dear Tom, 

How often has Mother Nature decided to play an April Fools’ Day joke with snow in the Chicago area? When did it last happen?

— Mark Orloff and Stephen Verhaeren, Palos Park

Dear Mark and Stephen,

It hasn’t happened often, but Chicagoans have dealt with 10 measurable April 1 snowfalls since 1885. Most recently, 0.9 inches fell in 2002, and a more significant 3.7 inches fell in 1993. Nature’s biggest April Fools’ prank occurred in 1970, when the city was hammered by a 10.7-inch snowstorm on April 1-2. Accompanied by thunder and lightning, the heavy, wet snow was piled into large drifts by northeast winds gusting to 52 mph. The weight of the snow caused much damage to trees, shrubs and power lines. The storm also forced the relocation of the then-annual preseason Cubs-White Sox City Series to Tulsa, Okla.

ASK TOM: What are the official rules for measuring snowfall?

Dear Tom,

What are the official rules for measuring snowfall?

— C. Michael Becker

Dear C. Michael,

Frank Wachowski, who has been measuring Chicago’s snowfall for nearly 60 years, provides this information:

Two measurements are taken: snowfall and snow depth.

Snowfall is measured on a snow board, a 2-foot square piece of plywood painted white to reflect heat, with a ruler to the nearest 10th of an inch. When falling snow does not accumulate, it’s reported as “trace — melted as it fell,” and if no measurable snow (0.1inches or more) occurs during the calendar day, a trace of snow is entered in the record books.

Snow depth is measured to the nearest inch. If drifting is a problem, many measurements from high spots to low spots must be averaged to obtain a representative reading

ASK TOM: What is black ice?

Dear Tom,

What is black ice?

— Jack Anderson, Glen Ellyn

Dear Jack, Black ice can be a major problem on cold mornings during snowmelt, as the moisture left from the melting snow refreezes. The ice forms a nearly invisible, thin layer on roads or sidewalks because it takes on the color of the underlying pavement, which on asphalt surfaces appears black. Black ice can also form from freezing drizzle, wind-blown snow or frozen condensation. It is dangerous because unsuspecting motorists or pedestrians traveling on dry pavement fail to realize they are on an icy surface and can fall or lose control of their vehicles. The term originally was used to describe a thin layer of ice on a pond or lake, but in recent years its use to describe the road hazard has become much more common.

ASK TOM: Recording seasonal snowfall in Chicago

Dear Tom,

I say that recording snow as part of the seasonal snowfall ends when we stop having snow, but my husband says it ends on the first day of spring. Who’s correct?

— Chris Schulz, Naperville

Dear Chris,

You are the winner on this one. Seasonal snowfall totals are the sum of all measurable snowfalls (0.1 inches or more) from the first snow in the autumn to the last snow in the spring. Over the 129-year span of the city’s snowfall records, the earliest measurable snow occurred on Oct 12, 2006, (0.3 inches) and the latest on May 11, 1966, (0.2 inches). This season the first measurable snow was logged Nov. 11, when 0.4 inches fell. Typically, Chicago sees its last measurable snow around April 3, but given our persistent chill this spring, it may be a while before we are declare the end of the 2013-14 snow season.

ASK TOM WHY: How fast do raindrops fall?

Dear Tom,

How fast do raindrops fall?

Dan Cox, Schaumburg

Dear Dan,

Raindrops come in various sizes, and the larger they are, the faster they fall. By definition, raindrops must possess diameters greater than 0.02 inch; smaller droplets are termed drizzle. Drizzle droplets (diameters 0.02 inch or less) are the slowpokes of the liquid precipitation world, descending at speeds of one to four mph. Raindrops (diameters greater than 0.02 inch) fall faster — from about five mph up to a maximum of 20 mph; the average fall speed is 14 mph. Photographic measurements show that the upper limit of raindrop size is one-fifth inch in diameter. At greater sizes, raindrops become instable and shatter into smaller drops. That size limit (diameter one-fifth inch) also caps the raindrop fall speed at 17-20 mph.

Ask Tom: Chicago-O’Hare’s weather records

Dear Tom, 

Did O’Hare keep weather records before it was named the official site in 1980? If so, what did it record during our benchmark winter of 1978-79?

— Phil Ordway, Chicago

Dear Phil,

Weather observations have been taken at O’Hare International Airport since October 1958. Before this season, seasonal totals there have topped 60 inches only four times: 67.7 inches in 1966-67; 61.3 inches, 1964-65; 83.7 inches, 1978-79; and 60.3 inches, 2007-08. So far this season, O’Hare has logged 80 inches and needs another 3.8 inches to set a new record for the airport. It would take another 9.8 inches to top the city’s official record total of 89.7 inches measured at Midway Airport in 1978-79.

The city typically records measurable snow through early April, so a new seasonal snowfall record is still possible.

ASK TOM WHY: Has it snowed in all 50 states?

Dear Tom,

Has it snowed in all 50 states?

Alex Penzel
Arlington Heights

Dear Alex,

Snow occurs most winters in 49 of the 50 states, Florida being the lone exception. Even tropical Hawaii experiences snow annually on the 13,000-foot-plus slopes of Mauna Loa and Mauna Kea, which actually become skiable several times each winter. While snowfall is a given in all of the north, the nation’s southern states also get snow, at least in the mountainous terrain. Northern portions of Florida, especially in the panhandle, experience some flurries in most, but not all winters. During a cold wave in February, 2010 snow blanketed much of the Deep South including northern Florida. On February 12 snow cover was documented in all 50 states when hikers in Hawaii photographed snow patches near the summit of Mauna Kea.

ASK TOM: Where did the expression “old man winter” originate?

Dear Tom, 

Where did the expression “old man winter” originate?

— Bill Traylor, Berwyn


Dear Bill,

The origin is unclear, but it likely goes back to pagan times. Old Man Winter, like Jack Frost, is a personification of winter and likely related to other terms like Father Winter, which has roots in Russian folklore as Morozko or Ded Moroz, a character similar to Santa Claus whose name translates to Old Man Frost. Other theories of origin relate it to a stages-of-life metaphor for the seasons where spring is youth, summer is adulthood, autumn is life’s past-prime slowdown and winter is old age, a season where vegetation dies and the landscape takes on a mantle of white like an old man’s hair.

ASK TOM: Cold February 2014 vs the cold of February 1899

Dear Tom,

How did the cold weather this February compare with the cold wave here in February 1899?

— John Dillon, Batavia


Dear John,

While February 1899 is remembered for the unprecedented record cold it brought to much of the South, Chicago was actually colder this February.

Last month averaged 17.3 degrees, compared with 17.9 degrees in February 1899. This February was also much snowier, logging 19.5 inches, compared with just 3.5 inches in 1899.

However, February 1899 does reign supreme in terms of extreme cold, with five days of minus 17 or lower.

That includes a low of minus 21 on Feb. 9, a day when the mercury dropped to minus 20 or lower across nearly the entire 400-mile length of Illinois.

ASK TOM: What is the latest occurrence of the first 60-degee day?

Dear Tom,

It seems like we’ve usually hit 60 a few times by now. What is the latest occurrence of the first 60-degee day?

— Nick Bilski, Munster

Dear Nick,

You are correct. Typically the city basks in its first 60-degree day by Feb. 28, but this year we’ve logged only days in the 50s. Since 1871, Chicago climatologist Frank Wachowski found, the city’s latest arrival of 60s occurred April 23, 1881.

However, in those days the official thermometer was where chilly lake winds often hindered spring warmth. Since the official temperature site was moved inland to Midway in 1942 and then to O’Hare in 1980, the latest onset of 60s was April 7, 1970. Chicago has recorded 60s every month of the year. Last year the first 60 was Jan. 29, when the mercury reached a balmy 63.