Dear Tom,
What month has had the most 6-inch or greater snowfalls here?
Nick Recchia, River Grove
Dear Nick,
Six-inch snowstorms: a child's delight and a motorist's nightmare. Chicago
has its share of such storms, to be sure, but, given its reputation as a
cold and snowy Midwestern city, not as many as one might suppose.
Chicago weather historian Frank Wachowski cracked open the record books to
provide the following snowy statistics. Based on 80 years of snowfall data
compiled at Midway Airport since 1928, the city has logged 112 snows of 6
inches or greater, an average of 1.4 per winter season.
Here's the monthly breakdown: November, 3 storms; December, 30; January, 25;
February, 26; March, 24; April, 4. Two surprises: April leads November; and
December, only the city's third-coldest month (behind January and February),
leads the pack.
ASK TOM WHY: October 2008 Archives
Dear Tom,
How does all the rain we had this summer compare to the rainiest places in the world?
Anna Spiczynski, Chicago
Dear Anna,
The world's wettest locations are on mountains or ridges situated so that prevailing
winds force moist oceanic air inland and upslope. In the United States, the wettest spot
is on Mt. Waialeale on the island of Kauai, Hawaii. The annual rainfall there is a
whopping 460.0 inches -- about 38 feet of rain -- or 12.7 times Chicago's annual
average of 36.27 inches.
With 43.28 inches of precipitation (rain plus the water content of melted snow) as of
October 25 at O'Hare, only an additional 6.08 inches is needed to establish a
new annual record (currently 49.35 inches registered in 1983).
The world's wettest location is Lloro, Colombia, with 523.6 inches (14.4
times Chicago's average). There, prevailing west winds carry in moist tropical air from
the Pacific Ocean.
Dear Tom,
What date and year has Chicago recorded its earliest measurable snowfall?
John Lustrup
Dear John,
Chicagoans don't think of October as a "snow month," but in fact October brings the
first snow of the approaching winter season in more than half of the years. A computer
scan of the city's official snowfall data set reveals that the first snow of the season has
occurred by Oct. 31st in 65 of 124 years, or 52 percent of the time.
Oct. 12 stands as the date of Chicago's earliest-occurring measurable snow in the
autumn: 0.3 of an inch fell on that date in 2006. However, Chicago weather historian
Frank Wachowski tells us that measurable snow has fallen even earlier in the season at
Midway Airport when 0.2 of an inch fell on Oct. 8, 2000, but Midway was not the official
observation site at that time (by then, O'Hare International Airport was, and still is, the
official site).
Dear Tom,
My husband likes to say that it "always rains on Halloween." I know that is not true, but
how many times has it rained on Halloween in the past 50 years?
E. Howard
Dear E. Howard,
Your husband is exaggerating, but there have been quite a few rainy Halloweens in the
last half century. Chicago climatologist Frank Wachowski noted that since 1958 at
least some rain (trace of more) had fallen on 27 of the past 50 Halloweens(54 percent).
The last two Halloweens here have been dry, but most recently rain fell 2005 and in
2003. In 1994 the city experienced its rainiest Halloween on record when 2.26 inches of
wind-driven rain soaked the area. Before midnight some western suburbs even reported
some snow. That rainstorm produced tragic consequences when 68 people perished in
a plane crash near Roselawn, Ind., a result of severe icing.
Dear Tom,
My great-grandchildren are old enough to trick-or-treat now and I've been telling them
about some very warm Chicago Halloweens that I remember back in the 1930s. Can you
refresh my memories so I give them more detail?
Clara Price
Dear Clara,
You must be recalling the Halloweens in 1933 and 1935 when the temperature peaked
at a summery 78 degrees. In fact, since 1871 only two Chicago Halloweens have been
warmer, 1950 when it reached 84 degrees and 1944 when the mercury hit 79. Not only
was Halloween 1933 warm but it was also dry, a great day for trick-or-treating, but in
1935 a steady rain fell after 8 p.m. putting a damper on the festivities. The city's last
truly mild Halloween was back in 2000 with a high of 70 degrees. In contrast, the
coldest took place in 1873 when the high was only 31 and the low 23 with some light
snow reported at times.
Dear Tom,
I am negotiating a snow removal contract for our homeowner's association.
How many snows of two inches or more does the Chicago area receive in a
typical winter?
Joseph Hudetz
Dear Joseph,
Chicago's snow records date back 124 seasons to the winter of 1884-85, and
the long-term averages show that the city receives measurable snowfall (0.1
inch or more) on 29 days each cold season and a snowfall of 2 inches or more
on six occasions. Of course, those numbers can vary tremendously depending
upon the nature of the winter. The city has never gone through a winter
without a 2-inch or greater snowfall but on two occasions, first in the
winter of 1921-22 and again in 1936-37, there was only one such event.
Compare that to the 15 2-inch-plus snowfall events during the snowy winter
of 1977-78, and you get an idea of the winter-to-winter variability in
snowfalls that Chicago has experienced.
Dear Tom,
How come we never hear of any hurricanes hitting the U.S. Pacific Coast?
Frances Lang, Glen Ellyn
Dear Frances,
Water off the coast is too cold. Eastern Pacific hurricanes usually develop from Baja,
Mexico, south to Central America, where the ocean water exceeds the 80-degree-plus
warmth needed for storm formation. Water temperatures plummet quickly northward
along the California coast, dropping into the 60s—a value prohibitively cool for
hurricanes. Farther north off Oregon and Washington, the water temperature is in the 50s.
On rare occasions, a Pacific hurricane will move north, hugging either side of the Baja
Peninsula and affect the southwestern United States. In September 1939, one of these
storms, known as El Cordonazo, brought gales and heavy rain to Los Angeles and San
Diego.
Dear Tom,
Your recent column regarding ragweed prompts me to write. When I was a
child, ragweed (also known as goldenrod) was considered extremely
detrimental to those with allergies and asthma, but nowadays this is not the
case. Why does no one connect this deadly ragweed to the terrible increase
in asthma cases?
Grace Hansen, Des Plaines
Dear Grace,
Goldenrod and ragweed are entirely different plants. The Great Plains Nature
Center in Wichita, Kan., says, "Goldenrod gets mistakenly blamed for the
agonies of hay fever sufferers in autumn. It blooms at the same time as
ragweeds, which are the real culprit. Ragweeds are pollinated by the wind."
Goldenrod pollen is fat and sticky, and carried by insects. It is not borne
on the wind like ragweed pollen. The Center explains, "People suffering from
allergies ... look for a flower to blame and goldenrod gets the rap because
it is so visible and abundant."
Dear Tom,
Why do typhoons and hurricanes have different names since the only
difference between them is location?
Pamela, Tinley Park
Dear Pamela,
Tropical cyclones are a global phenomenon developing in tropical waters both
north and south of the equator. The storms are given regionally specific
names including hurricane in the Atlantic, Caribbean, and northeast Pacific,
and typhoon in the northwest Pacific. These names have developed over time
primarily from the cultures located in the areas that they affect. The word
hurricane is thought to be derived from the word huracan, a Taino and Carib
god, or hunraken, the Mayan storm god. The word typhoon seems to have
originated either from the Cantonese t'ai fung (a great wind), the Arabic
tufan (smoke) or from the Greek typhon (a monster). In the Indian Ocean,
these storms are referred to only as severe cyclonic storms or tropical
cyclones.
Dear Tom,
Could you please explain what a front is? It is a very strange sounding term.
Mrs. Mary Toth
Dear Mary,
Like all areas of inquiry, meteorology has its own language of technical terms, many of
which undoubtedly sound strange to an unaccustomed ear. In the atmospheric
sciences, a front is the transition zone or boundary between two air masses of
significantly different characteristics.
Fronts are often a few hundred miles in length, sometimes over a thousand. In width, a
frontal boundary zone ranges from a few miles to about 50 miles. Air temperature and
moisture are two of the characteristics that cause air masses to differ, and in the usual
case one air mass is colder and drier than the other. A front can be stationary, but it
usually moves (though rarely faster than 40 m.p.h.). When colder air is advancing, it is
called a cold front; with warmer air advancing, a warm front.
Dear Tom,
I have some old family photos labeled "the farm after tornado March 25, 1942". The
farm was near Fairview in Fulton County, Illinois west of Peoria. Do you have any
information on this storm?
Bev Cherney
Dear Bev,
The picture may have been taken on March 25, 1942 but the tornado actually occurred
nine days earlier on March 16.
Several twisters struck central Illinois that day, an F4 storm that killed 11 northeast of
Champaign near Alvin, an F2 that hit near Yates City northwest of Peoria and the F2
tornado that struck your family farm. This tornado moved northeast on a 10-mile path
through Fulton County. The twister struck 13 farms causing damage estimated at about
$100,000. Many homes were torn apart and barns were destroyed. Eleven
people were injured in the storm but fortunately there were no fatalities.
Dear Tom,
I live on the ninth floor of a 14-story condo near Lake Michigan. What should I do in
the event of a tornado?
Sally J. Loeser, Chicago
Dear Sally,
The structural strength of skyscrapers, and even medium-rise structures such as yours,
far exceeds the stresses that tornadic winds could apply to them. Winds in excess of
100 m.p.h., sometimes much higher, occasionally buffet the upper reaches of Chicago's
higher downtown buildings in the winter, and channeling of winds between high-rise
buildings sometimes creates those extreme winds at lower levels as well.
Be advised, however, that windows will shatter and exterior walls may tear away. For
those reasons, the safest and most tornado-proof location in a condominium high-rise
or office skyscraper is an interior closet or an interior stairwell. Do not try to get to a
lower floor and do not use the building's elevators.
Dear Tom,
How long does it take for total darkness to set in after sunset?
Does the length of time vary by season?
Tina Bohlen
Dear Tina,
Astronomer Dan Joyce tells us that most widely recognized definitions
for darkness are civil, nautical and astronomical twilight which occur
when the sun sinks six, 12 and 18 degrees below the horizon
respectively. Once astronomical twilight ends, astronomers are assured
that no extraneous light will appear on their telescopic images. In
rural areas, most people will stop noticing atmospheric illumination
shortly after nautical twilight ends, but city dwellers will not perceive
much difference beyond the end of civil twilight. There are small
variances during the year but in general the time from sunset to the end
of civil twilight is about 30 minutes with another 30 minutes for
nautical twilight and an additional 25 minutes for astronomical
twilight.
Dear Tom,
Has Chicago ever recorded a temperature of 90 degrees or higher in the fall after a
sub-40 degree low?
Brandon D. Lade
Dear Brandon,
It hasn’t happened often, but we can find at least three such occurrences including one
just last year. On Sept. 15, 2007, Chicago set a record low of 39 degrees. Just nine days
later, on Sept. 24, warmth returned, and the city officially logged a high of 90. Similar
occurrences were noted in 1956 when after a 38-degree low on Sept. 20, the mercury
soared to 92 degrees just two days later on Sept. 22; and in 1951 when a 38 on Sept. 28
was followed by a 90-degree high on Oct. 4. Though 90s after 30s are rather
uncommon in Chicago, early season chills are often followed by warm-ups in the 70s
and 80s as northerly winds in the buckled jet stream that brought the chill move east,
putting Chicago in a warm southerly return flow.
Dear Tom,
Has a World Series game ever been snowed out?
Ed Berling, Lockport
Dear Ed,
Snow has fallen during at least three World Series games since the inaugural
Fall Classic in 1903, but no game has ever been snowed out. Prior to
baseball's expanded season and playoff structure, the World Series used to
be held in early October, so a major snowfall was never a concern. But now
with the final games potentially extending into November, the odds of a
postponement due to snow increase, particularly in the northern cities.
Ironically, two games that were played in snow flurries took place here in
Chicago during the 1906 World Series between the Cubs and White Sox on Oct.
9 and 11, 1906. More recently, snow showers fell during the late afternoon
on a very cold Oct. 22, 1997, in Cleveland during Game 4 between the Indians
and the Florida Marlins.
Dear Tom,
During many of the thunderstorms in Chicago this past summer, strong winds often
started up a few minutes before the rain began. Were any of those winds associated
with tornadoes?
Thad Courter
Dear Thad,
The winds that you have described are called thunderstorm outflow winds, and they are
not associated with tornadoes. Raindrops falling from a thunderstorm literally drag
down with them the air through which they are falling. Much more importantly,
raindrops also evaporate as they fall, cooling the air they pass through and making it
heavier. A current of strongly descending air thus develops in the rain area of the
storm. When that current strikes the ground, it rushes out ahead of the storm,
producing the strong (and sometimes damaging), gusty, cooling winds that typically
occur at the onset of a thunderstorm.
Dear Tom,
When was the last time there was measurable snow here in November?
Linda Coleman
Dear Linda,
There was measurable snow here last year when a total of 0.3 of an inch fell on Nov.
21 and 22 and also in 2006 when 0.4 of an inch fell on Nov. 30.
In fact, the city's last November without measurable snowfall was in 2001. Since the
city's snowfall climatology began in 1884, measurable snowfall (0.1 of an inch or more)
has been logged in 101 out 123 Novembers (81 percent). While the snowfall in most
Novembers is light, the city has had some exceptionally snowy ones and has endured
some major early-season snowstorms. Chicago's snowiest November was in 1940
when 14.8 inches of snow piled up. That month turned out to be the snowiest month of
the entire 1940-41 winter season that went on to produce 52.5 inches of snow.
Dear Tom,
While following the progress of Hurricane Ike and other hurricanes on a usually reliable
lightning detection website, I noticed few if any lightning strikes associated with the
hurricanes. Is this normal?
Brent Erwin
Dear Brent,
It is normal. Hurricanes contain very little, if any, lightning despite
popular belief to the contrary. The concept of "raging thunderstorms" in hurricanes is
erroneous.
Cumulonimbus clouds (thunderheads) become electrified when their vertical wind
currents cause raindrops and ice crystals to brush past each other; the "rubbing" causes
the particles to become charged. Hurricane winds, though, are mainly horizontal. They
lack the powerful, very localized vertical currents typical of thunderstorms. In addition,
hurricanes are tropical weather systems; they are warm throughout and they contain
little or no ice, even at great altitude.
Dear Tom,
What is the latest date of any 80-degree day here? How often has it reached that
temperature in meteorological fall?
Nick Recchia, River Grove
Dear Nick,
A computer scan of 138 years of Chicago's official temperature records dating from
Nov. 1, 1870, to the present reveals that every meteorological autumn (September
through November) has produced at least one day at or above 80 degrees. The same
can be said of meteorological spring (March through May) and summer (June through
August). An 80-degree day has occurred as early in the spring as March 3 (81 degrees,
1974) and as late in the autumn as Nov. 1 (81 degrees, 1950).
Winter (December through February) is the only season during which Chicago's
temperature has not reached 80. Nevertheless, the city's highest winter temperature is a
very unwintry 75 degrees (Feb. 27, 1976).
Dear Tom,
I remember several inches of snow falling in Chicago in October when I was a
kid. I'm guessing that it was in the early 1950s. Can you verify this event?
Bill Renner
Dear Bill,
The year was 1952 when 3 inches of lake-effect snow fell in the Chicago area
during the early morning hours of Oct. 20. A strong cold front passed
through Chicago late on Oct. 19 and temperatures plummeted as strong north
winds gusted to 40 m.p.h. The strong winds produced high waves on Lake
Michigan that flooded portions of South Lake Shore Drive. As the temperature
dropped, snow began falling shortly after midnight and continued into the
morning. Despite the still-warm ground the snow accumulated -- especially on
grassy areas. After a subfreezing morning low of 29 degrees, the temperature
climbed to 41 degrees, and the record early season snowfall was nothing more
than a melted memory.
Dear Tom,
How often has Chicago moved its official site for weather records?
Natalie Strauss
Dear Natalie,
Since the beginning of weather records here on Oct. 15, 1870, the city’s official climate
site has moved 13 times. The first official observations were taken at what is now 181
W. Washington St. from Oct. 15, 1870, until it was abandoned on Oct. 8, 1871, during
the Great Chicago Fire. After the fire, several downtown locations served as the official
site with the longest tenure at the U.S. Courthouse at 219 S. Dearborn St. Records
shifted to Rosenwald Hall at the University of Chicago on Jan. 1, 1926, until a move to
Midway Airport on July 1, 1942. Midway was the official site until a relocation to O’Hare
International Airport on Jan. 17, 1980. The official station has been moved around
O’Hare three more times, reaching its current location on Feb. 1, 1996.
Dear Tom,
Last week we saw what appeared to be frost on our rooftops in the early
morning even when temperatures were not even close to 32 degrees, and
probably much warmer on the roof of the house. Was that really frost?
William Brown, Aurora
Dear William,
It was frost. Frost forms when a layer of air cools below freezing and below
its saturation temperature by contact with a cold surface which itself has
chilled to a subfreezing temperature. Airborne water vapor condenses
directly, in ice crystal form, onto the cold surface and frost forms. (Frost
is not frozen dew.)
Under clear, calm, chilly nighttime conditions, surfaces like blades of
grass (but it works for rooftops, too) radiate a great deal of heat and
their temperature will drop sharply. If there is no wind, a thin layer of
very cold air develops, sometimes an inch or less in depth, and it is here
that frost forms.
Dear Tom,
Did Mrs. O'Leary's cow really start the Chicago fire?
-Jim Morris
Dear Jim,
Historians agree the Chicago Fire of Oct. 8-10, 1871, originated in the O'Leary barn,
but it is not clear that Mrs. O'Leary's cow kicked over a lantern. Daniel "Peg Leg"
Sullivan claimed in an inquiry on Nov. 25, 1871, he saw the cow start the fire. However,
investigation has since revealed Sullivan's testimony contained many inconsistencies;
the possibility that he himself started the barn fire is very real.
Regardless of the cause, Chicago was a tinder box waiting to ignite that
October. Only 0.74 inch of rain (19 percent of normal) had fallen in the five weeks
leading up to Oct. 8, a warm and very windy day with low humidity. Professor Increase
Lapham of the Chicago Weather Bureau later commented, "A dry season, a strong wind,
and an accidental fire, whenever they occur together, will do the work."
Dear Tom,
What are the sunniest and cloudiest months of the year in Chicago?
Kelly Spong Arlington Heights
Dear Kelly,
Thanks to the continuing efforts of Midway observer Frank Wachowski, Chicago has
one of the best sunshine data bases in the nation dating to 1893. Wachowski notes, not
surprisingly, that the sunniest months here are in the summer. June and July lead the
year, averaging 68 percent of possible sunshine followed by August with 64 percent.
The city will shortly be approaching the cloudiest time of the year, with November and
December averaging 40 percent and 39 percent respectively. The sunniest month on
record here was July 1916, when nearly cloudless skies allowed 95 percent of the
possible sunshine to bathe the city. In contrast, a scant 16 percent of the possible
sunshine reached the city in November 1985.
Dear Tom,
During my childhood in the early 1950s I remember spending most of my summers in a
swimming pool during very hot weather. Could you characterize the summers of the
1950s?
-John Skaritka Elgin
Dear John,
You were not alone in trying to escape the heat during the hot summers of the 1950s.
Based on average temperature, five of the city's all-time 10 warmest summers (June,
July, August) occurred during the '50s. The summer of 1955 with an average
temperature of 76.4 degrees holds the honors for being the city's warmest. That year
the city logged 46 days where the mercury reached 90 degrees or higher. Other
summers that decade with a lot of 90 degree plus days included 1953 (42), 1959 (39),
1952 (38), and 1954 (36). Based on Midway Airport data, the '50s brought Chicago
276 days of 90 degrees or higher, second only to the "Dust Bowl" years of the 1930s
that recorded 343 such days.
Dear Tom,
You publish a single high and low temperature forecast for Chicago. What site is that
for, and with all the variability around the Chicago area, how can you do that?
Jay Wait
Dear Jay,
The daily temperature forecasts are made for the city's official climate site at O'Hare
International Airport. However, great detail is provided in the supporting text to convey
the variability in weather that frequently exists around the vast metropolitan area,
further complicated by the proximity of Lake Michigan.
Temperature ranges are given from areas far inland to locations downtown or near the
lake or from far north to far south, depending upon the temperature distribution.
Efforts are made to pinpoint where the heaviest snow or rain is expected to develop.
Often winter storms track close to city bringing heavy snow to the northern suburbs, a
slushy mixture to the city and rain to southern sections.
Dear Tom,
My hay fever is getting worse year by year and doctors say the ragweed
pollen count is increasing. How is the weather causing this?
Irene Stack
Dear Irene,
It's not the weather but rather the steadily increasing concentration of
carbon dioxide (CO2) in the air. CO2 greatly stimulates the growth rate of
plants and their production of pollen, including ragweed. Atmospheric CO2
has increased 31 percent from 294 parts per million (ppm) in 1900 to 384 ppm
now. In response, ragweed (the source of pollen that triggers hay fever) has
doubled its pollen production since 1900. Dr. Paul Epstein of Harvard
University's Center for Health and the Global Environment, says, "This
carbon dioxide stimulation of plants has a side effect for public health,
(causing) hay fever, conjunctivitis and ... asthma."
Dear Tom,
I have seen photographs of lightning bolts flashing through giant clouds of ash rising
above erupting volcanoes. Is this trick photography? A lot can be done with computers
these days to alter photographs.
Jack Larsen, Chicago
Dear Jack,
The number of lightning flashes that occur worldwide in any given year is
immense—literally hundreds of millions of them. The annual tally just in the United
States runs at more than 100 million. An overwhelming majority of those bolts are
“standard” lightning flashes associated with thunderstorms, but friction between sand
particles in sandstorms will occasionally generate electric charges sufficient to produce
lightning. Lightning also frequently flashes through ash clouds above erupting
volcanoes for the same reason. The photographs you saw were probably not doctored.
Dear Tom,
On Jim Ramsey's WGN-TV weathercast a few years ago, he showed satellite
photographs in which cloud cover almost exactly matched the shape of the
Great Lakes. Other areas were clear but clouds over the lakes matched the
shape of the lakes. I found it very interesting. Cold weather effect?
Sharon Hrycewicz, Batavia
Dear Sharon,
Cold-weather effect it was. Very cold air over relatively warm water
stimulates the development of cumulus and stratocumulus clouds over the
water. It's practically a daily occurrence in the Great Lakes region during
the winter.
Usually, though, brisk winds constantly transport those clouds downwind and
over land. Sometimes, as in the situation that caught your attention,
minimal air motion allows the clouds to hover right where they form: over
the water.
Dear Tom,
My 10-year-old son asked, "Why does the sky turn green before a tornado comes?"
Charlie and Eric Mayer
Dear Charlie and Eric,
No one really knows for sure, but this much is certain: The greenish tint that
sometimes accompanies cloud structures in thunderstorms is not associated with
tornadoes. Many tornado-producing thunderstorms do not appear green and most
green-tinted thunderstorms do not produce tornadoes.
Please explain to your son that "green thunderstorms" are not reliable indicators of
tornadoes. Recent research suggests the greenish tint of some thunderstorms occurs
when they contain an especially great amount of water. Water selectively absorbs most
of the colors in sunlight but scatters out the green light. When sunlight passes through
such a storm, a disproportionately great amount of green light reaches our eyes.
Dear Tom,
The coldest temperature recorded in Antarctica is -129 degrees, and carbon
dioxide (CO2) freezes at -71. Has it ever snowed CO2 in Antarctica, or is
the percent of CO2 too low?
Alison Drabik, Oak Forest
Dear Alison,
Indeed, CO2 gas freezes at -71 degrees and winter temperatures in Antarctica
routinely drop below that frigid value, and on rare occasions in the Arctic
as well.
Meteorologist David Cook in the Climate Research Section at Argonne National
Laboratory in DuPage County says, "Certainly, at least some of the CO2 in
the atmosphere at the poles does freeze out (of the air) during the winter.
However, there is not enough frozen out to accumulate to any extent." This
is because Antarctic temperatures, as bitterly cold as they are, do not
remain below -71 degrees for much of the year. Also, atmospheric CO2
concentration is vanishingly sparse, at a meager 0.0385 percent.
