ASK TOM: Winter 2013-14′s cold temperatures

Dear Tom,

I believe this was among the coldest winters on record, and since Jan.1 this seems like one of the coldest starts to a calendar year in my memory.

— D. Baxter, Chicago

Dear D.,

Most area residents would agree with you. The winter (December through February) just ended ranks as Chicago’s fourth coldest. That’s the result of a computer scan of 144 winters in Chicago’s official temperature database (from the winter of 1870-71 through 2013-14).

With an average temperature of 18.8 degrees, it was 0.5 degrees warmer than the 18.3-degree average of the coldest winter, 1903-04.

And last winter’s chill has persisted into the spring. Through April 21, the average temperature for 2014 stands at 26.6 degrees, the city’s seventh coldest for that period (Jan. 1-April 21).  Coldest: 1875 at 25.0 degrees.

ASK TOM: Budding trees and cold spells

Dear Tom,

Are trees that begin sprouting after warm spells in March likely to suffer or be killed when cold spells occur after they have sprouted?

— Sharon North, Zion

Dear Sharon,

Probably not. That’s the word from Doris Taylor, plant information specialist at the Morton Arboretum. She says it would take a few weeks of abnormally mild temperatures in March followed by an outbreak of bitterly cold air (readings as low as zero degrees) to create serious problems for native trees.

Extended warmth in March would encourage magnolias, crab apple and other more sensitive trees to bloom earlier than usual. Their buds would not be harmed, but foliage would prove most vulnerable because those tissues are most sensitive. Other plants witha history of sprouting or blooming early deal with cold and snow quite successfully.

ASK TOM WHY: Was there a major snow storm on May 1 years ago?

Dear Tom,

My husband insists that there was a major snow storm on May 1st many years ago. Is he correct?

Phyllis Shugall
Morton Grove

Dear Phyllis,

It happened nearly 75 years ago, but your husband’s snowy memory is correct. The Chicago area received its heaviest May snow when 2.2 inches was fell on May 1-2, 1940 at the city’s official observation site on the University of Chicago campus. Following a balmy 73-degree high on April 30, temperatures plunged in the wake of a strong cold front. Rain began after midnight and changed to snow during the morning on May 1 and continued overnight finally ending the following afternoon. The snow forced the postponement of a game at Wrigley Field between the Cubs and Boston Bees. The snowfall was even heavier in other parts of the metro area with 3.7 inches at Midway Airport, 4.8 inches at Marengo and 5 inches at Elgin.

ASK TOM: Chicago’s biggest Easter snow

Dear Tom, 

What was Chicago’s biggest Easter snow?

— Bob Johnson,

Buffalo Grove

Dear Bob,

By the nature of Easter’s movable date, which can be as early as March 22 or as late as April 25, the weather on the holiday has greatly varied, ranging from wintry to summerlike. Since 1885 snow has fallen on 21 Easters, most recently in 2007. Most of the snowfalls have been minor events, but the holiday has hosted two major snowstorms.

On April 4, 1920, the city was hit by 6.4 inches of snow, but the biggest snowfall occurred March 29, 1964, when 7.1 inches fell. The snow began just before sunrise and lasted until about 5 p.m. Winds gusting to nearly 40 mph created near-blizzard conditions, with visibility dropping to less than one-quarter of a mile. An inch of snow also fell that Saturday.

ASK TOM WHY: Do you crack the windows in your house during a tornado?

Dear Tom,

I have heard you should crack the windows in your house during a tornado. Please give me your thoughts.

Rich Middleton, Rockford

Dear Rich,

Do NOT do that. It’s a notion conclusively laid to rest by research conducted in 1977 by an engineering team at Texas Tech’s Institute for Disaster Research and further discredited by all that’s now known about how tornadoes work. Opening windows in or near tornadoes is a useless exercise and a waste of precious time that ought to be used in getting yourself and those you are responsible for to a safer location. In fact, it may actually contribute to damage to the house.The pressure drop in the strongest tornadoes is about 10 percent, and that pressure decline can be vented by the normal openings in a house in just three seconds, even with the windows closed.

ASK TOM WHY: How many past Good Fridays have experienced rain or snow?

Dear Tom,

How many past Good Fridays have experienced rain or snow?

— Michael K. Garrison,

Dear Michael,

Good Fridays do show a bias toward precipitation. With the help of Chicago weather historian and climatologist Frank Wachowski, we checked the weather on 143 Good Fridays dating to 1871. Measurable precipitation has occurred in 73 years, or 51 percent of the days, at a time of the year when the daily climatological expectation for precipitation is about 40 percent. When traces of rain and snow are added to the mix, the percentage jumps to 64 percent as compared with an expectation of 56 percent. The last rain to fall on Good Friday was April 22, 2011, when more than half an inch soaked the city.

ASK TOM: Bright green streak falling star.

Dear Tom,

In late March I saw a bright green streak, a falling star. What accounts for that color? Air pollution?

— Frank Dezio

Dear Frank,

Meteoroids, orbiting the sun in huge numbers, are believed to be debris left over from the formation of the solar system.

They are occasionally captured by the Earth’s gravitational pull and, plunging at speeds up to150,000 mph, glow to incandescence because of friction with the atmosphere.

A brief streak of light, usually whitish, is the familiar result.

But astronomer Dan Joyce of Triton College tells us that a distinct green color is not rare.

The color of the streak has nothing to do with the atmosphere, he says.

The composition of the meteoroid is probably a reason for the color, and he suspects it is likely chromium.

ASK TOM: How are very abnormal temperatures figured into Chicago’s “normal” temps?

Dear Tom,

Over what period of time have Chicago’s daily normals been calculated? How are the very abnormal temperatures like our very cold winter figured into the normals?

— Tig White, Chicago


Dear Tig,

The National Weather Service’s National Climatic Data Center in Asheville, N.C., calculates the official normal daily high and low temperatures used in the U.S. By international agreement, normals are simple arithmetic averages of weather variables over 30 years, generally three consecutive decades, and they are recalculated each decade. Normals now in use cover the period 1981-2010.

Unusual temperatures are factored into the calculations just like any other readings.

Don’t overinterpret normal values. They don’t even represent what should happen; they are merely averages.

ASK TOM: What is an “embedded thunderstorm”?

Dear Tom,

What is an “embedded thunderstorm”?

– June Wheeler,  Madison, Wis.

Dear June,

Webster’s New World Dictionary defines “embed” this way: “To set or fix firmly in a surrounding mass.” The precipitation that falls with major storm systems often extends across areas as large as several Midwestern states. Meteorologists refer to these as “synoptic scale” events. This kind of precipitation distribution differs from the relatively narrow bands or isolated clusters of showers and thunderstorms that usually occur in the warm season.

When In a situation in which a large precipitation area includes scattered thunderstorms, those storms are said to be “embedded” within the larger precipitation area. A forecast of rain and embedded thunderstorms suggests an extended period of rain that might occasionally include a thunderstorm.

ASK TOM WHY: How windy was it for the May 17, 1979 Cubs game at Wrigley Field?

Dear Tom,

How windy was it for the May 17, 1979 Cubs game at Wrigley Field when the Phillies beat the Cubs 23-22?

Allen Moody
Island Lake

Dear Allen,

There have been windier days at Wrigley Field, but the wind was definitely blowing out on the afternoon of May 17, 1979. According to Chicago weather historian Frank Wachowski, south winds were blowing straight out to left field at 20 mph with gusts in excess of 30 mph during the game. There were 11 home runs hit that day, including three by Cubs’ slugger Dave Kingman and two by Mike Schmidt of the Phillies. After one inning the Phillies led 7-6 and the Cubs overcame as 12-run deficit to tie the game in the 8th, only to lose it in the 10th on Schmidt’s second homer,