Dear Tom,
I have memories of the oppressively hot Chicago summer of 1954. What kind of
winter followed?
John Jacob, Oak Park
Dear John,
The summer of 1954 was indeed a hot one in Chicago with 36 days when the
mercury reached 90 degrees or higher. There was one day of triple-digit
heat: June 25 with a maximum temperature of 100. The winter that followed
was one of Chicago's warmer ones, averaging 28.5 degrees or nearly 2 degrees
above the long-term winter average temperature of 26.7 degrees. It ranks as
the 46th warmest of 138 Chicago winters since 1870-71. Snowfall was subpar
with a season total of only 32.2 inches, substantially below the city's
current normal of about 40 inches. The snowiest month was December with 8.2
inches, followed by 6.5 inches in both January and February.
ASK TOM WHY: November 2008 Archives
Dear Tom,
How does "black ice" differ from regular ice, if it does?
-Dr. Leon J. Hoffman, Chicago
Dear Dr. Hoffman,
Black ice is just regular ice that forms in a thin layer on roads or sidewalks. It is almost
invisible because it takes on the color of the underlying pavement, which on asphalt
surfaces is black. It poses a major problem for unsuspecting motorists and pedestrians
who have been traveling on dry pavement and suddenly encounter loss of traction, failing
to realize they are on an icy surface. Black ice forms when moisture refreezes after a
snowmelt, from freezing drizzle, windblown snow or frozen condensation. The term
originally was used to describe a thin layer of ice on a pond or lake, but in recent years its
usage to describe a road hazard has become predominate.
Dear Tom,
In Chicago, which calendar date has the greatest deviation between the
record high temperature for the date and the record low temperature on that
same date? My guess is that it occurs sometime in March.
Bruce Brothers, Marengo, Ill.
Dear Bruce,
Actually, it happened in January -- Jan. 20, to be specific.
On that date in 1906, Chicago's temperature jumped to 63 degrees,
establishing a record high for the date, and on Jan. 20, 1985, the city
shivered at 27 degrees below zero, the record low for the date (and also the
city's all-time lowest temperature in official records dating from Nov. 1,
1870).
The range between those two temperatures (63 degrees and 27 below) is 90
degrees, and that stands as the greatest deviation between the record high
and record low temperatures on any single day of the year.
Dear Tom,
You reported that the record low for Nov. 21 was 1 degree set back in 1880.
How accurate is that measurement, and where in Chicago was it taken?
Tim Guimond, Evanston
Dear Tim,
That 1-degree record low on Nov. 21, 1880, was taken downtown at the city's
official observation site, then located at the Roanoke Building on the
southeast corner of Madison and LaSalle. The reading is quite accurate as
the temperature was measured with high-quality thermometers that recorded
the highest and lowest values for the day. It should be noted that the
record low of 1 degree was taken in the heart of the city, and it was even
colder that morning in outlying areas such as Elgin, which logged 3 below
zero. The high that afternoon was only 11 degrees, and that frigid reading
also established a record low maximum for Nov. 21.
Dear Tom,
Why don't we see lightning during snowstorms?
Cornelia Hatland, Evanston
Dear Cornelia,
Lightning does sometimes occur during snowstorms, and meteorologists have a
colloquial name for the phenomenon: thundersnow. It's a rare event, occurring in the
Chicago area only a few times in a given 10-year period.
The opaqueness of snowflakes and their sound-muffling fluffiness greatly limit the
distance that lightning can be seen or thunder heard during thundersnow events.
Typically during snowstorms, moist but relatively stable air flows gently up and over
colder air; it cools as it ascends and its moisture condenses into snow.
On rare occasions when a vigorous low pressure system is passing across the region
and it has drawn unstable air, usually of Gulf origin, into its wind system, the moist air
will surge into powerful rising currents that build into bona fide thunderstorms.
Dear Tom,
I've noticed that mild fall and spring days often experience large temperature drops
with rain changing to snow. What is Chicago's warmest day that has had measurable
snow?
Mike Velez
Dear Mike,
Chicago's weather has a reputation for rapid change and the passage of a strong cold
front is often the culprit. Climatologist Frank Wachowski notes at least 10 days since
1871 when the city has logged a temperature of 60 degrees or higher and had a
measurable snow. On April 22, 1910 the mercury peaked at a balmy 65 degrees then
crashed to 35 by midnight with 0.1 inch of snow. That little bit of snow was only the
beginning. Snow continued intermittently for the next four days with more than 6
inches falling through April 26. However, in true Chicago fashion, a rapid warm-up
followed and by April 29 the mercury soared to a summery 86 degrees.
Dear Tom,
If hurricanes feed off of water that is evaporated and if that occurs when the air
pressure is quite low, does this mean the boiling point of water varies depending on the
air pressure?
Carl Rollberg, Calumet Park, Ill.
Dear Carl,
Changes in air pressure do, indeed, affect the temperature at which water boils. The
boiling temperature falls as air pressure decreases (and as elevation increases).
Water, even cold water, evaporates at all temperature and air pressure values, and air
pressure is not a factor in providing moisture in hurricanes. Air pressure is not low
during the formative stage of a hurricane, and water vapor, from the evaporation of sea
water, is fueling the developing storm even then.
At sea level, water boils at 212 degrees; at 620 feet (Chicago's elevation), it boils at 211
degrees; but 1,450 feet up (the top of Sears Tower), at 208 degrees; in Denver, 202
degrees.
Dear Tom,
How do the heavy rains of last September compare to those of historical
record? My guess is that they were significant, but not the worst. I believe
urban development has exacerbated the flood effects of heavy rains like the
September rains.
Michael Katso, Munster, Ind.
Dear Michael,
The massive rains that swamped metropolitan Chicago in September were among
the heaviest, but, as you correctly noted, not the very worst. With 13.63
inches of rain, September 2008 was the city's third-wettest month ever,
behind August 1987 (17.10 inches) and September 1961 (14.17 inches).
However, rain of any given amount now produces more runoff and higher river
crests than ever before because urbanization increases the runoff of
rainwater up to six times what would occur on natural terrain. As the city
area grows and more land is made impervious to water absorption by roofs and
concrete, the flood threat also grows.
Dear Tom,
What are the Chicago records for the most days with rain, and also the most days
without even a trace of rain?
-Miguel Vasquez
Dear Miguel,
On average, Chicago receives measurable precipitation (0.01 inch or more) on one day out
of three, but the reality is that wet days tend to cluster together, as do dry days. In official
weather records dating from Nov. 1, 1870, Chicago’s longest dry spell was lengthy
enough literally to constitute a mini-drought: 22 days, Sept. 2-23, 1979. Not one drop of
rain fell during that period. The greatest number of consecutive wet days is 11, registered
on two occasions: Aug. 24-Sept. 3, 1880, and May 15-25, 1949. Rain wasn’t continuous,
but measurable rain fell on each of the days. Rain totals in those wet spells were 3.62
inches and 2.25 inches, respectively.
Dear Tom,
During a recent stay in Hawaii, we experienced a day of wonderful tropic
rain. A local insisted that Hawaii never gets thunderstorms because of the
islands' isolation in the Pacific waters. Can this be true? Why?
C. Michael Becker
Dear C.,
Surrounded as they are by unceasingly mild ocean waters, 75-82 degrees
through the year, the Hawaiian Islands rarely experience a day above 90
degrees. And because of the Islands' subtropical location, the atmosphere
above them is relatively mild to a height of several miles.
Thunderstorms, though, are children of a thermally unstable atmosphere: hot
air at the surface, very cold air aloft. Those conditions rarely prevail in
Hawaii, and strong Hawaiian thunderstorms are correspondingly rare, but
"never" is a powerful word. Honolulu averages seven weak thunderstorms
annually, Hilo 10, Kahului four.
Dear Tom,
In "The Day After Tomorrow," temperatures dropped so much and so fast that buildings
froze. How cold must it be for that to happen?
-Florian Stefan
Dear Florian,
The situation depicted in the movie, "The Day After Tomorrow," in which temperatures
plunged so suddenly that skyscrapers in New York City froze literally within a few
seconds, is a fantasy situation that could not happen in the real world. It was, after all,
a science-fiction movie. Even a reading of 129 degrees below zero, the world's lowest
temperature (recorded at Vostok, Antarctica, on July 21, 1983) would be far from
sufficient to cause massive structures like skyscrapers to freeze that quickly.
In the movie situation, bitterly cold air aloft suddenly descended to the surface. In
reality, sinking air compresses and warms at a rate of 5.4 degrees per 1,000
feet of descent.
Dear Tom,
Is it just my imagination or have we had our heaviest snows the last few winters during
December?
Ed Berling Lockport
Dear Ed,
Your perceptions may have been influenced by recent events. Last December was quite
snowy totaling 17.6 inches at O'Hare International Airport and 21.1 inches at Midway
Airport. While the month featured no huge snowstorms, frequent small snows quickly
added up making December 2007 the snowiest here since 2000, when 30.9 inches fell
at O'Hare and 41.3 inches at Midway. Other that those two years, December snowfall
totals since 1998 are far from spectacular. Six years had less than 6 inches and the only
other years with remotely robust totals were 2002 with 8.0 inches and 2005 with 10.4
inches. The city's normal December snowfall is 8.7 inches at O'Hare and 10.4 inches at
Midway, about 25 percent of our annual snowfall.
Dear Tom,
Why do trees grow buds in the winter when it is so cold?
Garrett Ricca (age 7), Naperville, Ill.
Dear Garrett,
Woody plants (like trees) that live for many years have the ability to survive through all
the different kinds of weather that occur during the course of the year -- warm
temperatures and thundershowers in summer and freezing cold weather and
snowstorms in winter. Trees cycle through an active growth phase in the warm part of
the year and a resting, or dormant, phase in the cold part.
They produce leaves and seeds in the spring and summer when days are long and
temperatures are warm, but as days grow shorter in the fall, they lose their leaves and
grow small "resting buds" that stay on the branches through the winter. That's what you
saw. Trees remain dormant in the winter but come out of their dormancy when warmer
temperatures return in the spring, and the cycle repeats.
Dear Tom,
What day of the year is Chicago's snowiest day?
Fran Kosey, Chicago
Dear Fran,
We can offer two answers to your question.
For starters, consider this: A total of 3,063.0 inches of snow was measured at Midway
Airport in the 79-year period from 1929 through 2007. That works out to an average of
38.8 inches per year. Measurable snow has occurred there as early in the snow season
as Oct 12 (0.3 inch in 2006) and as late as May 11 (0.2 inch in 1966). Jan. 13 stands as
Chicago's snowiest day, with a total accumulation of 54.6 inches in the 79 years of
Midway snow data. Jan. 26 ranks second with 51.5 inches.
The snowiest single day, midnight to midnight, in Chicago snow history is Jan. 2,
1999, when 17.6 inches buried the city. That day was part of an epic Jan. 1-3 storm
that delivered 20.6 inches.
Dear Tom,
This year we had our first snowflakes on Oct. 26. What are the earliest and
latest dates for the arrival of the season's first snow?
Greg Simmons
Dear Greg,
The long-term (since 1884) average date for the season's first snowflakes is
Oct. 31, but the date from one year to the next can vary considerably. The
city's earliest encounter with snow took place on Sept. 25 -- first in 1928
and again in 1942. The latest arrival of the first snow occurred nine years
ago in 1999. Following a snowless October and November, Chicago finally
logged the season's first snow on Dec. 5th when 0.1 inches was recorded, the
start of a lackluster season that produced only 30.3 inches of snow.
Dear Tom,
Florida has apparently gone through this hurricane season affected only by Tropical
Storm Edouard. I’d like to move there. Is any part of the state less prone for hurricanes?
-Molly Nellis
Dear Molly,
The entire state is vulnerable. With three coastlines, Florida is a target for hurricanes
approaching from the Gulf of Mexico, the Caribbean and the Atlantic. Since 1850 more
than 110 hurricanes have made landfall there with the Panhandle and northwest most
vulnerable, followed in decreasing order by hits in the southeast, southwest and the
northeast. Because Florida is a long, narrow state, hurricanes can easily move across the
state with little decrease in intensity. In Florida’s nightmare 2005 season, Hurricane
Wilma produced more damage in southeast Florida than it did after its landfall in the
southwest part of the state.
Dear Tom,
You recently wrote about an 8.6-inch snowfall around Thanksgiving in 1975.
Was that Chicago's biggest November snowstorm?
Haley Wilson
Dear Haley,
It was not, actually coming in third behind a 12-inch storm on Nov. 25-26,
1895, and a 9.3-inch windy, slushy snowfall that blasted the city on Nov.
6-7, 1951. That snow, which began early in the morning of the 6th, became
very heavy by the evening rush hour. It brought traffic to a standstill and
caused many to abandon their vehicles. One-hour bus trips turned into
four-hour-travel marathons as howling east winds piled the wet snow into
huge drifts. The strong winds produced high waves on Lake Michigan that not
only flooded shoreline areas but also crashed onto outer Lake Shore Drive,
closing it to traffic.
Dear Tom,
Is there a word for that stuff that falls from the sky that is not snow or sleet, but looks
like tiny pieces of Styrofoam?
R. Mitchell
Dear R.,
It's called graupel, frozen (as opposed to liquid) precipitation in the form of roundish,
white grains of soft ice that resemble tapioca. They are easily crushed and often break
apart after they rebound from hard surfaces. Graupel is also commonly referred to as
"snow grains" or "soft hail." The latter designation is misleading because hail, typically
associated with thunderstorms, is an entirely different kind of frozen precipitation.
Snowflakes, as they descend through clouds, sometimes encounter supercooled water
droplets -- liquid water that has cooled, without freezing, to a temperature below 32
degrees. Supercooled droplets freeze onto snowflakes falling through them, coating the
flakes with rime ice; the result is graupel.
Dear Tom,
While camping in the "north woods" (300 miles north of Winnipeg, Canada), we saw the
aurora borealis. How high up do auroras form?
John Lutz
Dear John,
Dr. Fredrik Carl Stormer (1874-1957), a professor of mathematics at the Institute of
Theoretical Astrophysics in Blidern, Norway, pioneered the use of photography to study
auroras in the early 1900s. He and his research team simultaneously photographed
auroras from many different locations and, by means of triangulation and geometry,
calculated the height in the atmosphere at which they occur.
Stormer found that auroras occur in two separate "zones of activity," --a lower zone
about 50-200 miles above the Earth's surface and an upper zone 350-630 miles aloft.
Stormer also found that most auroras originate in the lower zone.
Hello, Tom,
I can remember a very, very cold Thursday morning in early November of 1991. Did the
temperature dip below zero that morning, because my car wouldn't start and many
schools were closed?
Jerrold Petrizzo, Lemont, Ill.
Dear Jerrold,
Thursday, Nov. 7, 1991, was indeed a cold day across northeast Illinois, but
temperatures did not dip below zero. Chicago's temperatures that day ranged from an
afternoon high of 27 degrees to an overnight low of 13, the latter being a record low for
the date.
The entire period from Nov. 2-9 was cold throughout, with daily lows ranging
from 11 to 19 degrees and highs from 24 to 38 degrees. (Normal lows then are in the
middle 30s, highs in the low 50s.) Snow flurries and very light snow occurred
intermittently on five of the eight days, but total snow accumulation for the
eight-day period was less than one-half inch.
Dear Tom,
We had a major Thanksgiving Eve snowfall a few years ago. My dad said he remembered
another Thanksgiving Eve snowstorm back in the 1970s. Which storm was bigger?
Sally Watson
Dear Sally,
The storm that your father recalls was a huge one totaling 8.6 inches on Nov. 26-27,
1975. Snow fell furiously through Wednesday afternoon and evening and when it finally
ended on Thanksgiving morning a total of 8.6 inches had fallen at Midway Airport. That
storm was twice as big as the preholiday snowstorm a few years ago on Nov. 24, 2004
in which 4.3 inches fell. Both storms severely impacted air travel and traffic crawled on
snow-covered highways.
Significant snow around Thanksgiving is not all that common in Chicago. Using the
"White Christmas" standard of 1 inch of snow on the ground on the holiday, the city has
logged only 11 "White Thanksgivings" dating back to 1884.
Dear Tom,
Are we expecting a snowy or a dry winter this time around? Last winter was
not fun.
Geno Santiago
Dear Geno,
The National Weather Service's Climate Prediction Center recently released
its outlook for the December through February period. For the Chicago area,
averaged through those three months, the outlook anticipates a 50 percent
chance of above-normal temperatures, a 33 percent chance of near-normal
temperatures and a 17 percent chance of below-normal temperatures. Thus, the
outlook favors an increased chance of above-normal temperatures.
The outlook also indicates equal chances of above-normal and below-normal
precipitation. That means no clear climatic signal exists pointing to one
scenario more than another. Keep in mind "precipitation" does not equal
"snow." It refers to the liquid equivalent of rain and snow combined.
Dear Tom,
The problem of global warming is on everyone's mind these days, but aside from that,
what other environmental issues should we be concerned about?
-Bill Wright
Dear Bill,
Global climate change (not just global warming) heads the list of environmental
issues but other environmental challenges abound. Many of them concern fresh water,
which is increasingly in short supply as human population expands and demand
increases. Pollution of existing supplies is a growing problem worldwide. Another
environmental concern: Poor agricultural practices that lead to soil erosion and
degradation of soil quality which reduces crop yields. Other concerns: Deforestation,
desertification, air pollution and species extinction due to habitat loss and climate
change. And, rising sea levels increasingly threaten densely populated coastal areas.
Dear Tom,
I used to hear about cloud seeding to create rain, but I don't hear much
about it anymore. What is cloud seeding, and why has it faded away?
Donna Sweetser
Dear Donna,
Cloud seeding is controversial. Thorny legal issues often arise with the
process, and many states have banned it.
Cloud seeding involves adding certain chemicals to clouds, usually to
stimulate cloud development and enhance rainfall production, but there can
be other uses (such as hail suppression) as well.
Cloud seeding does not "create" rain. Rather, it encourages a cloud on the
verge of producing rain to produce more rain than it otherwise might. Many
scientists are skeptical of the results, and meteorologists point out that
clouds favorable for seeding often don't exist when drought conditions
prevail, whereas irrigation systems, though costly, guarantee the desired
benefits.
Dear Tom,
Has Chicago ever recorded a low temperature of 70 degrees of higher in
October?
Brandon D. Lade
Dear Brandon,
October lows in the 70s are quite rare in Chicago, having occurred on only six
occasions since records began in 1871. Not surprisingly, all but one of these took
place in the month's opening week. The only balmy night Chicago ever logged beyond
the first week occurred on Oct. 21, 1979. After a 78 degree high on Oct. 20, brisk south
winds kept the following morning's low from dropping below 70. Later that day the
mercury soared to a summer-like 84 and by midnight remained at a mild 73. Then a
cold frontal passage brought showers and falling temperatures with readings at a more
seasonable low of 45 by day's end on Oct. 22. Chicago's last October low in the 70s
was 71 on Oct. 4, 2005.
Dear Tom,
I have counted 21 jet contrails in the sky at one time. Why do some contrails dissipate
quickly and others linger and grow?
Marty Kelly, Janesville, Wisc.
Dear Marty,
Contrails, those white streaks of ice-crystal clouds trailing behind high-flying jet
aircraft, form when water vapor produced by the burning of jet fuel condenses into
visible cloud particles. Once formed, the lifespan of contrails depends on the amount
of moisture in the air.
In dry air, contrails will rapidly evaporate and disappear. In moist air, contrails linger for
hours, often growing and expanding from additional condensation.
Contrails in parallel lines result from aircraft moving through flight corridors --
"roadways" in the sky established by air traffic control centers. Aircraft
passing near waypoints -- "intersections" in the sky -- produce criss-crossing
contrails.
Dear Tom,
My parents who both grew up on Iowa farms always talk about the 1940 Armistice Day
storm. How did that storm impact Chicago?
Ann Montgomery LaGrange Park, Ill.
Dear Ann,
The Nov. 11, 1940 Armistice Day storm was one of the worst to ever hit the
Midwest. Ahead of the storm the region was basking in 50-60 degree warmth in the
strong southerly flow preceding the storm. As the storm passed, cold air slammed into
the region on howling 50-70 m.p.h. winds, turning rain to snow as temperatures
plunged to single-digits causing hunters to freeze to death. Blizzard conditions
developed across Iowa and Minnesota where snow drifted as high as 15 feet. In
Chicago, the mercury reached a balmy 63 degrees at 11 a.m. then fell to 20 by midnight
and to 16 by the following morning. Winds here peaked at 65 m.p.h. damaging
buildings, trees, power lines, knocking down signs and blowing out hundreds of
windows.
Dear Tom,
As a skier, I am always concerned about "avalanche weather" in the mountains out west.
What weather is most conducive to avalanches?
John Barsema
Dear John,
Jeff Renner, author of Northwest Mountain Weather, comments, "Just as
fresh snow offers wonderful conditions in which to play, it also increases the avalanche
hazard."
To assess that hazard, Renner says you should know the weather conditions that
preceded your ski outing. Avalanches generally occur during or within 24 hours of a
major snowstorm. The risk is greater when a storm starts at cold temperatures and then
it warms. This puts wetter, heavier snow on top of less-dense snow, an unstable
situation. A rule of thumb: Beware when freezing levels are forecast to rise. Winds
above 15 m.p.h. also increase the risk, allowing the snow to pack into a slab that
can let go if disturbed.
Dear Tom,
I saw many earthworms this past summer, what with all the rain. Any
explanation?
William Fie
Dear William,
The bodies and organs of earthworms are obviously very different from ours,
but their unique bodies enable them to live their underground lifestyle
efficiently.
A spokesman from the University of California (Berkeley) Lawrence Hall of
Science explains, "Earthworms require oxygen just as we do, but they have no
lungs. Instead, blood pumped by a series of five simple hearts flows close
to the worm's surface (and) absorbs oxygen and releases carbon dioxide
directly through the moist skin.
"For this reason earthworms can live for some time in water if the oxygen
supply is adequate. They don't drown per se, but may suffocate if the oxygen
content is low. This is why worms leave the soil and crawl on the sidewalk
during a heavy rain -- they are seeking oxygen."
Dear Tom,
You once published a list of Chicago’s coolest autumns, and the autumn of 1871 (when
Chicago burned) was among them. Surprising, because I always thought hot weather led
up to the fire. Also, your story about Peg Leg Sullivan was interesting.
--Claire Johnson
Dear Claire,
The Chicago Fire raged Oct. 8-10, 1871. That autumn, with an average temperature of
49.1 degrees (4.1 degrees below average), ranks as the city's seventh coolest out of 137
years. That it was so cool comes as a surprise, but the essence of the disaster was a
preceding two-month drought, high winds on the fire days and a tinder-dry city
constructed mostly of wood. Mrs. O’Leary’s cow kicked over a lantern, thereby igniting
the fire--or so claimed Daniel "Peg Leg" Sullivan in questionable testimony (but, at the
time, unchallenged) that he gave at a post-fire inquiry.
