Ask Tom Why

Dear Tom,

When I was a child living in New York (Brooklyn) my mother would tell me about the “Blizzard of (18)88” with the snow drifts up to the second floor of their house. Do you have details on that storm?

Thanks, Anne K. Canapary River Forest

Dear Anne,

The “Blizzard of 88” was one of the greatest Nor'easters in U.S. history. The storm, dubbed the “Great White Hurricane”, paralyzed the East Coast from Chesapeake Bay to Maine sinking ships and halting land travel. It struck after an early March warm spell stalling off the New England coast where it raged from March 11-14. It dumped more than 40 inches of wind-driven snow on portions of the Northeast and was responsible for more than 400 fatalities--200 in New York City alone where wind gusts reached 75 mph and the snow drifts towered to 30 feet.

Dear Tom,

What is the latest in the year that it’s snowed in Chicago?

--Rick, Chicago

Dear Rick,
Believe it or not, Chicago has recorded a trace of snow in June. It fell on a chilly June 2, 1910, a day with a high of 55 and a low of 43. A thunderstorm (probably during the early morning hours) brought a mixture of rain, hail, and snow pellets.
Rainfall that day totaled 0.41 of an inch, and snowfall was recorded as a trace (an amount too small to measure).
Other than that lone June event, the city’s latest-occurring snowflakes were traces on May 25, 1924, and May 26, 1889, and the latest measurable snow on May 11, 1966, with 0.2 of an inch.
The earliest snow flurries in fall occurred Sept. 25, 1928, and again in 1942, making July and August the city’s only totally snow-free months.

Dear Tom,

Why is there such a long time lag between heavy rains like the kind that we recently experienced and river cresting?

Raymond Strauss,
Grayslake

Dear Raymond,

Hydrologist Bill Morris of the Chicago National Weather Service Office explains, "Many factors affect the lag time between the end of the heaviest precipitation and the crest on a river: the size of the watershed, rainfall distribution over the watershed, rainfall intensity, land use, and antecedent conditions before the rain began, such as soil moisture. For widespread rainfall events, the size of the watershed is a major factor. Because the terrain here is relatively flat, it takes considerable time for water to move through larger watersheds like the Fox River in northeast Illinois. Smaller creeks will generally respond much more quickly to heavy rainfall."

Dear Tom,

In early 1855, my great-grandparents could not travel by train from Chicago to Galva, Ill., because of a big snowstorm. Can you provide any details?
— Audrey Walker, Woodstock
Dear Audrey,
Details are sparse, but with the help of Chicago climatologist Frank Wachowski we were able to piece together bits of information about the snowstorm.
The blizzard hit Jan. 20-21, 1855, affecting much of northern and central Illinois with heavy snow and extremely strong winds.
Newspaper accounts talk of snow drifts 6-8 feet high in Chicago that isolated the city, halting all travel and mail delivery. Strong winds produced a great deal of damage in the city, taking the roofs off some homes.
Travel in and around Chicago was still difficult in early February.

Dear Tom,
What is the science that explains why lightning makes our grass greener?
-- Gary, Willowbrook

Dear Gary,

The greening of grass and other vegetation is a positive benefit of lightning.
Plants require nitrogen, potassium and phosphorous for good growth. Nitrogen is used in the greatest quantity and must be constantly replenished.

It is estimated that global thunderstorms produce up to 175 billion pounds of nitrogen annually.

A lightning strike generates tremendous heat (50,000+ degrees F), “fixing” or combining normally inert atmospheric nitrogen with oxygen, which then combines with rainwater to form dilute nitric acid.
When this falls to Earth, it combines with other soil minerals, yielding plant-fertilizing nitrates.

Dear Tom,

Do the local National Weather Service offices do any weather research?

- Jason Marrs

Dear Jason,

In the early 1990s, the weather service created the position of "science and operations officer" (SOO), one at each of its 118 weather forecast offices. Ken Labas, then science and operations officer at the Chicago office, offers these comments: “The practice of meteorology in the (weather service) is primarily structured for providing forecasts and weather warnings, but there is a continuing need for training in both the science and the use of new tools used to monitor and forecast the weather. ... The (science and operations officer position) SOO is unique in that it allows an opportunity to work with the latest tools used in operational meteorology as well as do limited research on topics of local interest.”

Dear Tom,

The snow on April 19 after all that rain was a surprise. I know April weather can be crazy, but what about May? Has Chicago ever had snow in May?

--Giselle Marks, Western Springs

Dear Giselle,

Accumulating snow (0.1 inch or more) is a rare occurrence in May, but it does happen, on average, in one May out of 14.

Chicago’s greatest May snow event occurred on May 1-2, 1940, when nearly two inches of cold rain changed to wet snow before ending. In the aftermath, 2 to 4 inches of slushy snow blanked the city area. Officially at the University of Chicago observation station, 2.2 inches of snow accumulated; Midway Airport reported 3.7 inches during the same event. Wintry temperatures only in the 30s on May 2 rebounded to an afternoon reading of 75 degrees on May 5.

Dear Tom,

This has to be one of the coldest March 1-April 20 periods that Chicago has experienced. Is that true?

— Pat Byrne, Hoffman Estates

 
Dear Pat,

It might seem like we're experiencing a record cold spring, especially because the winter was relatively mild. That raised hopes that spring warmth would arrive early and persist, but it was not to be.

A check of the city's temperature statistics indicates that the period in question was, in fact, among Chicago's colder early springs but far from the coldest.

With an average temperature of 37.1 degrees, it was the 30th coldest in 143 years of temperature records dating from 1871.

The March 1-April 20 period this year was 3.4 degrees below the long-term average of 40.5 degrees but 4.1 degrees above the coldest: 33 degrees in 1926.

Dear Tom,
The extreme drought persisting in the Great Plains is reminiscent of the Dust Bowl years of the 1930s. What was the cause then? El Nino? La Nina?

-- Richard Miller, Chicago

Dear Richard,

The drought of the 1930s (and resultant “Dust Bowl”) was a seven-year event of varying intensity with 1930, 1934 and 1936 the worst years. Researchers have offered theories as to the cause, but none has been definitive.

The causes might never be known. The atmosphere wasn’t monitored by weather balloons back then, so we don’t have information about wind patterns and jet stream configurations. The drought occurred over such an extended period that no single El Nino or La Nina event (which usually runs only a year or two) or sunspot cycle (11 years) adequately explains the drought period.

Dear Tom,

What is evaporational cooling? What causes it? Can it happen at any time of year?

Steve Hanan, Morton Grove

Dear Steve,

Evaporation is the physical process in which a liquid is transformed to its gaseous state. A familiar example is water transforming to water vapor -- that is, evaporating. The process occurs at all times of the year, though much more rapidly at hotter than colder temperatures. Evaporation occurs when water molecules at or very near the liquid surface obtain enough velocity as a result of chance collisions with other molecules to escape into the air. Because the molecules that escape (evaporate) have above-average energy, the average energy of those left behind (the liquid) falls and the liquid cools – “evaporational cooling.” This explains why we feel a chill when we are wet and water evaporates from our skin.