ASK TOM WHY: February 2009 Archives

Dear Tom,
Sometimes March "comes in like a lion." What is the worst March 1 weather that Chicago
has experienced?

Red McCarthy, Plainfield

Dear Red,
It is hard to pick Chicago's worst March 1, but we can offer some strong contenders. In
both 1947 and 1948, March arrived with a major snowstorm. In both years the snow
continued into March 2, bringing the city more than 7 inches. March's opening in 1932
was raw, damp and blustery—temperatures were in the 30s with gusty northeast winds the
city was soaked by nearly an inch of rain. And just two years ago in 2007, 1.09 inches of
rain doused the city. In 1962, March opened as a "cold lion" with a high of 18 degrees and
a low of 5 below zero. Of course, there have been some years when March opened like a
lamb. One of the nicest was in 1992 when the high soared to 71 degrees.

Dear Tom,
Early afternoon on Jan. 21 the national radar picture showed some snow off
of lakes Erie and Ontario, and patchy rain over California, but nothing
elsewhere. Has there ever been a time when the whole nation was dry?
Joseph Morgenstern
Dear Joseph,
Precipitation-free periods might occur across the 48 contiguous states,
though only rarely and briefly.
Retired meteorologist Robert Johns, a 40-year veteran with the Storm
Prediction Center, says, "The most likely period for a few dry hours would
be the fall (probably late September or October) after low-level moisture
has been swept out of the nation and before the cold blasts needed for Great
Lakes snow/rain bands have developed. During this period you would need a
west-to-east weather pattern with the jet stream displaced north into
Canada, possibly with a weak high pressure system over the north and central
Plains."

Dear Tom,
What is the average date of the last snowfall? What is the earliest date that we have
been done with snowfall for the season?
Nick Recchia, River Grove
Dear Nick,
Spring is fast approaching and the recent smattering of mild days has raised hopes that
the harsh winter we've been enduring is finally behind us.

However, Chicago's snow history suggests caution is in order. Snowfall records dating
from the winter of 1884-85 provide these sobering statistics: Chicago's average last
date of measurable snow (0.1 inch or more) is April 3 --- five weeks away. March runs
a 96 percent chance of bringing measurable snow, and in April it's 52 percent.
Measurable snow has fallen as far into the spring as May 11 (0.2 inch on May 11, 1967).

At the opposite extreme, the city's snow season ended as early as Feb. 27 in the mild
"El Niño" winter of 1996-97.

Dear Tom,
Is it just me, or has this winter been more sunny than usual?
Mark
Dear Mark,
Chicago weather historian Frank Wachowski confirms your suspicions: This winter has
been considerably sunnier than usual. That's a ray of good news in a winter that in
other respects has been quite harsh by historical standards. Wachowski reports that, as
of Tuesday (Feb. 24), this winter (Dec. 1- Feb 24) has been the 18th sunniest since the
inception of sunshine records in the city in 1894 (115 years ago).

Winter days are "shorter" (that is, the hours of daylight are fewest at that time of year)
and winter is also Chicago's cloudiest season -- a double whammy that makes this
time of year seem especially gray and gloomy. As of Tuesday, Chicago's sunshine this
winter stood at 51 percent of the maximum amount possible, versus a normal winter
reading of 43 percent.

Dear Tom,
Has Chicago ever had a winter in which it recorded 20 inches of snow in three separate
months?
Pat Byrne Hoffman Estates, Ill.

Dear Pat,
A winter with three months of 20-inch plus snowfall has never occurred in the Chicago
area since records began in the winter of 1884-85.

The closest we've come was back in the winter of 1977-78 when only January, with
32.3 inches, exceeded the 20-inch threshold, but that December logged 19.2 inches
and February 19.7 inches.

So far this winter we've received more than 20 inches of snow in both December (21.9)
and January (21.5), but to date February has produced only a meager 4.5 inches. Unless
March or April turns out to be a blockbuster month for snow, the city's record of never
recording three 20-inch snow months in one winter will continue.

Dear Tom,
On a recent Hawaiian trip the paper not only listed the actual time of sunrise and
sunset but also times for civil, nautical and astronomical twilight? Can you explain?

Joe Kirasich western Springs
Dear Joe,
The time of sunrise and sunset is defined as the moment when the top of the sun's disk
is on the horizon. Civil, nautical and astronomical twilight are defined as when the sun
is six, 12 and 18 degrees below the horizon, respectively, as it is rising or setting. The
times as determined by U.S. Naval Observatory are used to define the gradual changes
in visible light that occur between total darkness and sunrise or sunset. Astronomer
Dan Joyce tells us that there are small time variations during the year, but there is
generally a period of almost 90 minutes for the transition from total darkness to
sunrise or from sunset to total darkness.

Dear Tom,
The boiling point of water varies with air pressure. What about the freezing
point?
Russ Scott, DeKalb
Dear Russ,
Changes in air pressure do affect the freezing point of water, but the
effects are vanishingly small.
Dr. Christopher Grayce, Professor of Chemistry at the University of
California (Irvine), explains, "The freezing point of water increases with a
decrease in the pressure applied to it. Hence the freezing point of water
will be less at high altitude and low pressure. But this effect is small.
The freezing point of water rises a mere hundredth of a degree per
atmosphere of decrease in pressure."
That is, the difference is air pressure values between sea level and the
farthest upper reach of the Earth's atmosphere, say 500 miles aloft,
provides a freezing temperature increase of only 0.01 degree. For all
practical purposes, the freezing point remains unchanged.

Dear Tom,
You often mention "buckling jet streams," but that term confuses me. Could you please
amplify?
George Burger

Dear George,
Jet streams are belts of very strong winds found within a narrow depth in the atmosphere,
usually 6 to 9 miles aloft. Because these winds often steer the movement of surface air
masses and weather systems, weather forecasters pay them close attention. Jet streams
form in the boundary zones ("baroclinic zones") between warm and cold air. When masses
of warm and cold air relocate, jet streams buckle to conform to the new boundary's
position. It's a complicated process because pockets of wind maxima embedded within jet
streams often trigger the development of surface storm systems that, in turn, shift the
positions of warm and cold air, further distorting the jet stream. The process feeds on
itself.

Dear Tom,
How many times has Chicago had snow on the first day of spring (March 20 or
21)?
Bill Ooms, Alsip
Dear Bill,
Chicago winters are long enough and harsh enough to make us anxious for
spring, but don't be fooled. The beginning of spring comes so early that it
falls well within Chicago's normal snow season.
For people in the atmospheric sciences, spring (so-called meteorological
spring) begins on March 1. In Chicago, measurable snow has fallen on that
date in 24 of the 124 years since snow records began here in 1885 -- about
one year in five (one in 5.2). The greatest amount: 4.6 inches in 1947.
Astronomical spring, defined as the date of the vernal equinox, occurs on
either March 19, 20 or 21. Measurable snow has occurred here 22 times on the
vernal equinox, or one year in six (one in 5.6, actually). The biggest
storm: 6.0 inches on March 20, 1964.

Dear Mr. Skilling,
What is the best and worst that can happen around here, snow-wise, in the winter?
Mildred Dudek

Dear Mildred,
A whopping 4,563.1 inches of snow have fallen on Chicago (excluding this winter)
since the inception of snow measurements in 1884. That averages to 36.8 inches per
winter but, as your question implies, snowfall varies greatly from year to year.

Oddly, the city's two least snowy winters and its two most snowy winters were each
back-to back affairs. The winters of 1920-21 and 1921-22 brought 9.8 and 11.5
inches, respectively; the snowiest winters, 1977-78 and 1978-79, put down 82.3 and
89.7 inches, respectively.

However, Chicago weather historian Frank Wachowski once remarked, "Weather records
are made to be broken," and the point is well taken. Chicago's snowfall records are not
carved in marble; it's only a matter of time -- those records will fall.

Dear Tom,
How far south in this country does subzero weather occur? Has it ever dropped below
zero in Texas or Florida?
Josh Sauerman Crown Point, Indiana

Dear Josh,
Florida has recorded a below zero temperature, but only once. On Feb. 13, 1899, with
an historic cold wave gripping the eastern half of the nation, the mercury dipped to
minus 2 degrees at Tallahassee. At the south end of the state, Miami's all-time low
temperature is 27 degrees and Key West's is 41.

Subzero weather does occur in Texas, especially in the north and in the higher
elevations of the west. The record low for the state of Texas is 23 below zero observed
at Seminole, located southwest of Lubbock near the New Mexico border at an altitude
of nearly 3300 feet. Farther south in Texas, the record low for San Antonio is zero,
recorded on Jan. 31, 1949.

Dear Tom,
You have mentioned that salt particles in the air act as condensation nuclei for cloud
formation. Where does that salt come from?
Joseph Mathias

Dear Joseph,
Every cloud that passes overhead is a visible collection of myriad particles
consisting of water droplets or ice crystals or both; and every cloud particle began its
life as a so-called condensation nucleus on which water molecules collected. The
collection process is called condensation when the resulting cloud particle is a water
droplet and sublimation when the resulting particle is a tiny ice crystal.

Chief among condensation nuclei are specks of sea salt, even thousands of miles into
the interior of continents. Droplets of salty ocean spray, when they evaporate, leave
their tiny burdens of salt floating in the air, to be disbursed through the atmosphere
and around the world.

Dear Tom,
What are the temperature ranges for it to snow?
Dennis Finn, Geneva, Ill.
Dear Dennis,
Snowflakes form in clouds only when in-cloud temperatures are below freezing (32
degrees). When in-cloud temperatures are above freezing, condensation produces water
droplets and rain. Usually, though, air temperatures at ground level are different --
sometimes higher, sometimes lower -- than temperatures in snow-producing clouds.

Chicago's biggest snowstorms generally occur with readings from about 25 to 32
degrees, but we have had snow with temperatures as high as the lower 40s and, on rare
occasions, below zero. Two inches of snow fell on Jan. 14, 2009, when the high/low
temperatures were 14 degrees and 2 below zero; nearly an inch of snow came down on
Jan. 10, 1982, with a temperature of 15 below zero. Snow routinely falls in Antarctica at
or below minus 50.

Dear Tom,
Ducks are often seen in lakes (fresh water) when Chicago's temperatures are
below zero. The 32-degree water must seem warm to them. When it is 40 below
in polar climates, how "warm" would the sea water be to the penguins?
Shawn Groom, Palatine
Dear Shawn,
Pure water freezes at 32 degrees. Water molecules, which tumble about
loosely when in the liquid state, become ordered in a crystalline lattice
during the freezing process. (By the way, the lattice structure encloses a
bit of space; that's why water "expands" when it freezes into ice.) However,
foreign particles in water (such as sodium and chlorine ions from dissolved
salt) hinder the formation of the crystalline structures because they
interfere with intermolecular forces between the water molecules. The result
is that the freezing temperature of salt water drops, sometimes into the
middle 20s.

Dear Tom,
Last Tuesday, we just missed breaking a record high that stood since 1876. What are
Chicago's longest-standing temperature records?
-Ken Kapson, Chicago

Dear Ken,
According to Chicago climatologist Frank Wachowski, the city's longest standing
temperature records are back-to-back lows set Dec. 4 (6 degrees below zero) and Dec.
5 (minus 8), 1871, just about a year after the city's climate records launched in late
1870. Chicago's longest-standing record highs date back to Dec. 31, 1875 (a balmy 68)
and the following day when it reached 65. The Feb. 10, 1876, record high of 63 that we
fell just short of last week is the city's third-oldest record high on the books.
Wachowski also noted that a 62-degree record high on Jan. 12, 1871, has never been
surpassed, but because it was tied on Jan. 12, 1890, the later date is the one in the
record book.

Dear Tom,
In my astronomy class I learned that century years were not supposed to have
a leap day. Why then did February 2000 have 29 days?
Marlene Fisher, Blanchard, Mich.
Dear Marlene,
Most people are familiar with the fact the leap years occur in years that
are divisible by four. However, if a year is divisible by 100 (century
years) it is not a leap year unless it is also divisible by 400. That is why
1700, 1800 and 1900 were not leap years, but 2000 was. There will not be a
leap day in 2100, 2200 and 2300 but there will be one in 2400, the next
century year to have a Feb. 29. Leap days are needed to keep the calendar in
sync with the seasons.
A tropical year, defined as the time between successive vernal equinoxes, is
365.2422 days -- so adding a leap day every four years keeps the alignment
differences between the calendar and the seasons fairly insignificant.

Dear Tom,
What kind of weather does the moon have?
Kenny Birks (age 10)

Dear Kenny,
The moon has no weather at all -- and that sounds pretty bleak, don't you think? The
kinds of events that come to mind when we think about "the weather" -- wind, clouds,
precipitation (like rain, snow, sleet and hail) and storms of all kinds (such as
thunderstorms, tornadoes and hurricanes) -- all those phenomena are children of the
Earth's atmosphere.

Our language is sprinkled with words that we commonly use to describe the weather --
hot, warm, cool, cold, humid, rainy, cloudy and fair, to name a few. You can probably
think of many more, but all of them would be useless if you were on the moon because
the moon has no atmosphere, none at all, and so it has no weather. The moon's gravity
is so weak that it cannot keep gases like the kinds that make up our air from escaping
into space.

Dear Tom,
Why can I hear airplanes and other far-away sounds so much better the colder it gets
outside?
Mark Barberis
Dear Mark,
Distant sounds can be heard more clearly in frigidly cold air than in warm air. Because
outdoor activity is reduced and fewer people are stirring about when it is very cold,
individual sounds are easier to distinguish.
The most important factor, though, is the great difference in the thermal structure of
the lower atmosphere when it is cold versus when it is hot. When air temperatures
change along the path that sound waves are traveling, the waves always bend toward
the colder air. In bitterly cold arctic air masses, the coldest temperatures are at the
ground with higher temperatures above; sound waves do not disburse upward readily.
On hot days, it's just the opposite: It's hottest at the ground and cooler above; sound
waves bend up and away.

Dear Tom,
Why is Aurora always colder than everywhere else?
Chad D. May
Assistant Principal/Athletic Director
Lake Zurich Middle School South
Lake Zurich, Ill.

Dear Chad,
Jim Allsopp, Warning Coordination Meteorologist at the Chicago office of the
National Weather Service, explains: "The weather observation is taken at the
Aurora Airport which is actually in Sugar Grove, about eight miles west of
downtown Aurora. It is a rural setting and it is not representative of
temperatures in the city of Aurora.
"The airport sits in a low spot. On nights with conditions favorable for
strong radiational cooling -- clear skies, light winds -- cold air, because
it is more dense, settles in low spots and valleys. The Sugar Grove weather
equipment is regularly maintained and calibrated by NWS technicians and it
is in good working order."
The Sugar Grove weather observations provide necessary information for
aviation operations and are not intended for other purposes.

Dear Tom,
What is the latest date we've ever had a temperature below zero?
Deborah Morgan, Batavia, Ill.
Dear Deborah,
Winter is winter and low temperatures are to be expected, but the frequency of frigid
weather this winter is testing the patience of even normally stoic Chicagoans. We're
beginning to hear questions like yours -- variations on "How much longer can this
last?" The answer, based on a computer scan of Chicago's temperature history, is: Quite
a bit longer. A sub-zero reading has been recorded here as late March 22, when the
city's temperature hit 1 degree below zero. Needless to say, that was an extreme event,
but temperatures this winter have tended toward the extreme. With an average
temperature of 19.3 degrees, the December-January period entered Chicago's record
books as the city's 10th coldest, and the coldest in 26 years.

Dear Tom,
The polar regions experience very short days in the winter, but the tropics
still have long days. The question is, do the polar regions receive as much
sun as the tropics? I would think not.
Martin Eck
Dear Martin,
We posed your question to astronomer Dan Joyce of the Cernan Earth and Space
Center at Triton College, and he provides this uncharacteristically brief
answer, "This is going to kill me, given my propensity for the long haul,
but, in a word, the answer is 'yes!'"
And that says it all. Cloudiness aside, long summer days and short winter
days in the Earth's polar regions offset each other, thereby exactly
preserving the annual average of six months of daylight and six months of
darkness. And that is also true everywhere else on the planet -- in the mid
latitudes (Chicago's location), in the tropics and at the Equator, and at
the North and South Poles.

Dear Tom,
Has every one of the 50 states recorded a temperature of 100 degrees or higher?
Rev.Ray Cosentino, Homer Glen

DearRay,
Yes, all 50 states have reached the century mark, but our two newest states barely made
the cut. The only time Alaska reached triple digits wason June 27, 1915, with a high of
100 degrees at Ft. Yukon. Pahala, on the Big Island of Hawaii, holds the honors for that
state’s hottest day with a 100-degree high on April 27, 1931. With the exception of New
England, where the all-time state highs hover around 105, the rest of the country’s
highest readings have topped 110 degrees. Illinois’ hottest is117 degrees set at East St.
Louis on July 14, 1954. The nation’s hottest reading, a blazing 134 degrees, was recorded
at Greenland Ranch in Death Valley, Calif., on July 10, 1913.

Dear Tom,
My dad claims Chicago had a winter in the late 1970s in which it did not
snow from Feb. 1 forward. Given the heavy snows we had in the winters of the
late 1970s, I am skeptical. Is my dad correct?
Tom Shute
Dear Tom,
Your dad is incorrect. Winter is still going strong in February, and it's
asking a lot for the entire month to be snowless. Even March, with rapidly
warming temperatures, is often a snowy month. Together, they have produced
at least some snow from Feb. 1 onward in every winter since records began
here in 1884.
But let's not be too harsh. In all likelihood, your dad was recalling the
bitterly cold and record-snowy winter of 1978-79. By Feb. 1, 79 inches of
snow had buried Chicago, and it was widely speculated the winter total would
top 100 inches. However, the pace of snow abruptly diminished, and the
season ended with "only" 89.7 inches.

Dear Tom,
The lowest temperature so far this winter has been 18 degrees below zero. That seems
colder than we usually get in the winter here in Chicago. How many winters have had a
lower temperature than 18 below?
Paul Rubin

Dear Paul,
Your hunch is correct. A computer scan of Chicago's entire official temperature data set
(138 years of records from the winter of 1870-71 to the present) reveals that only 12
winters have produced a reading lower than the temperature of 18 degrees below zero
recorded here on Jan. 16. And that was the city's lowest temperature in 13 years --
since 19 below zero on Feb. 3, 1996.

On average, the coldest temperature recorded during the winter at O'Hare Airport is 11
degrees below zero. Over the last ten years, however, with relatively mild winters, the
lowest temperatures each winter have averaged only 6 below zero.

Dear Tom,
My husband is still upset with me for not picking him up after work on
Valentine's Day 1990. Can you remind him why I didn't?
Fran Fredricks, North Aurora
Dear Fran,
You were smart to stay home that evening. Valentine's Day 1990 left a legacy
of undelivered flowers and canceled dinners as a major snowstorm brought
Chicago to a standstill. Snow began shortly after noon and quickly became
heavy with visibilities dropping to near zero. The storm reached peak
intensity during the evening rush hour as strong northeast winds gusting to
more than 30 m.p.h. piled the heavy snow into huge drifts. Snow-clogged
streets were littered with abandoned cars. The storm raged through the early
morning hours of Feb. 15, blanketing the area with 8-12 inches of snow.
Downstate, the storm produced freezing rain and sleet that encased much of
central Illinois in ice.

Dear Tom,
I saw that January 2009 was the 10th coldest January in Chicago history, but
where does it rank among Chicago's all-time coldest months?
Derek Bogdan, Chicago
Dear Derek,
A computer scan of Chicago's entire temperature data set from Nov. 1, 1870,
to the present -- a period comprised of 1,659 months -- identified the
city's coldest 20 months. Sixteen of the "bottom 20" were Januarys. No
surprise there, because January is the core of the cold season and, in any
given winter, it's usually the coldest month.
January 2009 was, as you noted, the 10th coldest January on record with an
average temperature of 15.9 degrees. But when the ranking includes all
winter months, it drops to the city's 13th coldest month. Nine Januarys were
colder, as was December of 1983 (14.3 degrees), February of 1875 (14.6
degrees) and February of 1936 (15.3 degrees).

Dear Tom,
Feb. 3 marks the 50th anniversary of the plane crash that killed Buddy
Holly, the Big Bopper and Ritchie Valens, and I read that the crash was
weather related. Can you provide any details?
Keith Mullen
Dear Keith,
The plane carrying the three rock stars took off from Mason City, Iowa,
around
1 a.m. on Feb. 3, 1959. Temperatures were around 20 degrees, and light snow
was falling. Weather reports indicated poor visibility as well as icing and
turbulence in the clouds. The pilot was not adequately advised of the
deteriorating weather conditions. In total darkness with snow falling and a
snow-covered landscape, the pilot lost the horizon and was forced to rely on
instrumentation he was not familiar with. The plane slammed into the ground
shortly after takeoff, killing all on board.

Dear Tom,
A recent question dealt with brutally cold back-to-back weekends in January
1982. Weren't all four Sundays that month extremely cold? Was that our
coldest month ever?
Malcolm Vye
Dear Malcolm,
January 1982 averaged a frigid 12.2 degrees and ranks as the city's fourth
coldest month on record. The only colder months here have been January 1977
(10.1 degrees), January 1912 (11.9 degrees), and January 1893 (12.0
degrees). Actually, January 1982 had five Sundays, and three of them
registered subzero readings. The first Sunday, Jan. 3, was relatively mild
with a high of 35 and a low of 30. The 10th and 17th were extremely cold
with high/lows of minus 4/minus 26 and 4/minus 23 respectively. Jan. 24 was
the third straight subzero Sunday with a high/low of 3/minus 3. The month
ended on a slightly milder note with a high/low of 21 and 10 on Jan. 31.