WGN Weather Center Blog

Dear Tom,
While sailing on Lake Michigan, the sun is both overhead and reflecting off the water
on a sunny day. Does the addition of the reflecting sun change the exposure time for
getting a sunburn on water versus on land?

Gerald Migely, Chicago

Dear Gerald,
"The higher incidence of skin cancers in sailors and farmers was one of the first
clinical clues that ultraviolet (UV) radiation is a carcinogen." Said Dr. Bryan Schultz, an
Oak dermatologist. "Most of the risk for sailors is in the long exposure times, but the
percent of UV reflected is also a factor."

Water reflects only about five percent of light when the sun is high, but the shiny
surface of a boat may approach 80 percent. "This does increase one's UV dose
significantly," Schultz said. UV reflection increases as the sun drops below 45º, but
those rays, filtered through more atmosphere, are much weaker.

Posted by wgnweather at 9:32 PM | Permalink | TrackBacks (0)

Dear Tom,
I have observed high-altitude jets dispensing heavy, non-dissipating trails behind them,
unusual in that they expand across the entire sky, turning a once-blue sky into a
complete cover of milky white. Tom, these are not condensation trails.
--Jeff Blondell
Dear Jeff,
Ah, but they are. Water vapor is one of the gaseous products of combustion and, when
added to the air in the exhaust of jet engines, condenses into visible clouds of ice
crystals--the wispy, cirruslike clouds that we see as condensation trails (contrails)
behind high-flying jets. Temperatures and humidity at flight altitude determine whether
contrails form and how long they last. In dry air, contrails will not form, or they will be
small and evaporate in a few seconds. In moist air, they persist for hours, often
"seeding" their own further growth.

Posted by wgnweather at 10:37 PM | Permalink

Dear Tom,

What might be the relationship between clouds and fog? Is low-lying fog actually a
cloud?

—Leon J. Hoffman, Chicago

Dear Leon,
Physically, clouds and fog are identical. Both are visible aggregates of water droplets
(or ice crystals) so small that they are nearly suspended in the air. Clouds differ from
fog only in that, by definition, fog is either at the ground or within several feet of it,
whereas the bases of clouds are aloft. It’s a convenient shorthand to say that cloud
and fog droplets are “suspended” in the air, but that is technically incorrect:
Thedroplets do fall. The fall rate is so slow—generally only 1 foot per minute, or less
—that, for all practical purposes, clouds and fog appear to be suspended. A final
distinction: Meteorologists also consider a visible concentration of smoke or dust
aloft to be a cloud.

Posted by wgnweather at 7:36 PM | Permalink | TrackBacks (0)

Dear Tom,
My son, age 7, has become deathly fearful of thunderstorms. Short of professional help, can you offer any suggestions?
James Smith, Madison, Wis.
Dear James,
The high winds, beating rain, lightning and crashing thunder of violent storms prove humbling to all of us, but they can be especially frightening to children. Here are a few tips that will allow you to confront and ease children's storm fears: Communicate with them—don't deny their fears. Let them know it is normal to feel afraid and explain that the storm will end. Remain calm and cool. Children take behavioral cues from parents and react accordingly. Shelter family pets during a storm so children will know they are safe. Assure children that lost or damaged toys, articles of clothing, etc., can be replaced; explain that it is more important that the family is safe.

Posted by wgnweather at 11:02 PM | Permalink

Dear Tom,

Years ago, I remember hearing seiche (pronounced saysh) warnings mentioned for
Chicago's lakefront. Could you please explain that phenomenon?

Royse Cramton, Oak Park, Ill.

Dear Royse,

In the Great Lakes Region, any sudden rise in the water level in a harbor or on the
shore of one of the Great Lakes is known as a seiche. In extreme cases, the rise,
occurring within a minute or less, can be several feet. Such dramatic events obviously
present great danger to people at the lakeshore.

The Chicago seiche situation is unique. In rare cases, an air-pressure jump in
advance of southeastward-moving thunderstorms can push a low surge of water
from Chicago across Lake Michigan. Upon striking the Michigan/Indiana shore, the
surge reflects back to, and focuses upon, Chicago's lakeshore,initiating a sudden,
temporary rise in the lake level.

Posted by wgnweather at 9:33 PM | Permalink | TrackBacks (0)

Dear Tom,
Why do we name hurricanes and typhoons but not tornadoes?
Stan, 11 and Ted, 9, Jatczak, La Grange Park

Dear Stan and Ted,
Tropical cyclones are named to enable better communication between meteorologists
and the public. Frequently multiple storms are active and naming the storms reduces
confusion and helps the public keep the storms straight.

In 1950, previously anonymous Atlantic Basin tropical cyclones were named using the
phonetic alphabet (Able, Baker, Charlie, etc.). From 1953 until 1978 only women’s
names were used, but starting in 1979 lists of alternating women’s and men’s names
were developed, a system still in use today.

It also makes sense to name tropical cyclones because they can roam the oceans for
days or weeks, while most tornadoes last for just a few minutes.

However, significant tornadoes or major tornado outbreaks are named after the fact,
like the Oak Lawn tornado or the Palm Sunday tornadoes.

Posted by wgnweather at 9:34 PM | Permalink | TrackBacks (0)

Dear Tom,

I'm old fashioned and I like to hang my wash outside to dry, but I only do this during
the summer. Would clothes still dry even in colder winter temperatures? Would it be
worth trying?
-Marlene Forst

Dear Marlene,

A sunny day is conducive to hanging your wash out anytime, but you will be
disappointed during the colder months.

Drying (evaporation) rates are a function of the air's ability to hold moisture, and this
is determined by temperature. Cold air has a very small capacity to hold moisture,
and a full day on the line on a cold day might still result in damp or frozen clothes.

Sunshine itself has a minor effect, raising the temperature of the clothes and adjacent
air molecules a few degrees.

Indirectly, though, sunny skies usually indicate a dry air mass and, hence, increased
evaporation.

Posted by wgnweather at 9:50 PM | Permalink | TrackBacks (0)

Dear Tom,
Are tornado warnings ever issued for funnel clouds?
-Patricia Nesbit

Dear Patricia,
A meteorologist would not hesitate to issue a tornado warning based on a
funnel cloud if the report appeared to be reliable and could be associated with a
Doppler radar that shows a rotation in the clouds in the area.
A funnel cloud becomes a tornado when it hits the ground. During periods of severe
weather, it could only be a matter of seconds before a funnel reaches the ground and
starts causing damage.

Storm spotters and weather professionals often use the redundant phrase “tornado on
the ground” to convey a sense of urgency and danger to the public about an
approaching twister. The redundancy makes it clear that the storm is an actual tornado
and poses an immediate threat.

Posted by wgnweather at 10:05 PM | Permalink | TrackBacks (0)

Dear Tom,
What is the date of Chicago's latest freeze?
--Shirley Bell
Dear Shirley,
Chicago's latest freeze occurred 16 years ago when the mercury fell to 32 degrees at
O'Hare International Airport on May 25, 1992. The previous morning was also chilly with
a frosty low of 34 degrees, and back-to-back minimums of 33 followed May 27-28.
Just six years ago, the city experienced its second-latest freeze when the thermometer
registered 31 degrees May 21, 2002. These freezes stand out because they are a full
week later than the previous latest freeze set May 14, 1895, with a low of 32. The two
latest freezes were established at O'Hare's more rural environment, which fosters
somewhat lower minimum temperatures than the city's earlier official thermometer
sites, which were near the lake until 1942 and then at Midway Airport through 1979.

Posted by wgnweather at 10:34 PM | Permalink

Dear Tom,
What is the difference between a hurricane, a cyclone and a typhoon?
—Jessica Vega

Dear Jessica,

There is no difference. Unfortunately, meteorological jargon and popular usage
variously apply different or overlapping meanings to those three words. In
meteorological parlance, a cyclone is a lowpressure system. Hurricanes and typhoons,
too, are low-pressure systems, but they are a specific kind of cyclone—tropical
cyclones (logically, cyclones that form in the world’s tropical and subtropical zones).
Hurricanes (in the Atlantic Ocean), typhoons (western Pacific Ocean) and cyclones
(Indian Ocean and Australia) are different names for the same type of storm. In
popular usage in the United States, “cyclone” is applied loosely to tornadoes,
waterspouts, dust storms, hurricanes and even to any strong wind.

Posted by wgnweather at 7:24 PM | Permalink | TrackBacks (0)

Dear Tom,
A lot of Chicago's moisture comes from the saltwater Gulf of Mexico, so why isn't our
rain salty?
Bob Johnson, Oak Park
Dear Bob,
Since the beginning of time, the saltwater oceans have been the reservoir of about 97
percent of this planet's water supply. The water is constantly being recycled,
evaporating into the atmosphere and returning to Earth as rain or snow in an ongoing
hydrologic cycle. Sea water is indeed salty, with about 35,000 parts of salt per million
parts of water. However, the salt in sea water is only dissolved in it and not chemically
bonded, so it is left behind when the water evaporates, like when a pot of saltwater is
boiled dry on a stove. That is the reason sea air is salty when the ocean's spray
evaporates, and also why precipitation falls as fresh water. When salty ocean water
surges inland as in a hurricane storm surge, it can kill vegetation.

Posted by wgnweather at 1:21 AM | Permalink

Dear Tom,

The Myanmar cyclone disaster is horrific. What could account for such a catastrophe?
Steve Bartik

Dear Steve,
The disaster in Myanmar, formerly known as Burma, is staggering. The official death
toll, now at more the 20,000, could climb to 100,000 as a worst-case possibility, said
Shari Villarosa, the U.S. chargé d’affaires in Yangon.

On the evening of May 2, Cyclone Nargis moved from west to east along Myanmar's
southern coast. It brought sustained winds of 125 m.p.h. and a 12-foot storm surge
that swept across the flat, low-lying and densely populated delta of the Irrawaddy
River.

The river branches into several large channels that drain south into the Indian Ocean.
Unfortunately, the north/south orientation of those channels allowed the cyclone's
onshore winds to push storm surge many miles inland.

Posted by wgnweather at 9:56 PM | Permalink | TrackBacks (0)

Dear Tom,
Please define the "growing season." When does it start and end?
Gregg Dubin, Huntley, Ill.

Dear Gregg,

No single definition of "growing season" is satisfactory for all situations.

Generally speaking, the growing season is the period of the year during which air
temperatures remain continuously high enough for the growth of cultivated plants.

A commonly accepted standard is the number of days between the average dates of
the last spring and first fall occurrences of a temperature of 32 degrees. By that
measure, the growing season varies from 191 days (April 17 to Oct. 24) along
Chicago's lakefront to 162 days (May 1 to Oct. 9) in outlying suburban locations.

Ideally, the growing season should be defined biologically rather than
meteorologically because plant species vary greatly in their tolerance to cold
temperatures.

Posted by wgnweather at 9:16 PM | Permalink | TrackBacks (0)

Dear Tom,
Weather-knowledgeable friends say large hail always comes before a tornado, but I
wonder about that. Is it true?
Peter Micham, southwest suburbs of Chicago
Dear Peter,
It is not true. Only the wind fields within and in the area several miles around a severe
thunderstorm provide reliable clues as to the storm's tornado-producing capabilities.
Unfortunately, those telltale signs are rarely apparent to an observer. Only Doppler
radars can detect them.

Severe storms forecaster Roger Edwards of the National Weather Service's Storm
Prediction Center in Norman, Okla., says: "Does hail always come before a tornado?
Rain? Lightning? Utter silence? High winds? Not necessarily for any of those. Hail can
indicate the presence of an unusually dangerous thunderstorm, but it is not a reliable
predictor of tornado threat."

Posted by wgnweather at 9:53 PM | Permalink | TrackBacks (0)

ATW GRAPHIC HEADER LINK:

Dear Tom,

I've noticed that sounds carry better at night than during the day. Could you provide
an explanation?

Louise, Park Forest

Dear Louise,

Sounds do carry better and farther at night. Because it tends to be quieter then,
individual sounds are easier to distinguish. By far the most important factor, however,
is a difference in the temperature structure of the lower few hundred feet of the
atmosphere between day and night.

Sound travels through cold, dense air more slowly than through warmer, less dense
air. When air temperatures change on the path along which sound waves are
traveling, the waves always bend toward the colder air.

By day, it's warmer near the ground and colder above; sound bends up and away from
the ground (and you). At night, it's colder near the ground and warmer above; sound
waves bend down.

Posted by wgnweather at 9:33 PM | Permalink | TrackBacks (0)

Dear Tom,
On a visit to the Black Hills of South Dakota, my family and I noticed outdoor neon signs
had screens over them for protection from hail. Is hail that frequent there?
--James Walker, Madison, Wis.
Dear James,
It is. Large hail is massively damaging. It flattens crops, shatters windows, dents cars and
kills birds and small mammals. Chicago experiences an average of two days per year with
hail. Most of it is small and causes no damage. But the frequency of hail, and especially
the frequency of large, damaging hail, increases steadily westward from Chicago. Hail is a
costly problem in the Great Plains, especially across Wyoming and Colorado. Cheyenne,
Wyo., with nine hail days annually, is the "hail capital" of the nation. The Black Hills, 200
miles northeast of Cheyenne, logs six hail days per year.

Posted by wgnweather at 10:36 PM | Permalink

Dear Tom,
What U.S. city has the most sunny days in a calendar year?
—Paul Pincawis, Elgin.

Dear Paul,
Few weather and sky phenomena lift our spirits more than a bright, sunny day,
especially after a cold, cloudy and snowy winter such as the one we have just put
behind us. Unfortunately, sunny days are often at a premium in Chicago and across
the Great Lakes region, and the area’s residents will not be surprised to learn that
they dwell in one of the nation’s cloudier areas; only New England and the Pacific
Northwest are cloudier. On average, Chicago logs 84 sunny days per year, well ahead
of cloudy cities like Seattle or Burlington, Vt., (58 days at both cities), but trailing far
behind cities in the nation’s desert Southwest. Yuma, Ariz., heads the list with 242
sunny days per year, followed by Phoenix (211) and Las Vegas (210).

Posted by wgnweather at 7:00 PM | Permalink | TrackBacks (0)

Dear Tom,
I love hot weather. When does Chicago usually record its first 90-degree day? When
was our last 100-degree day?
--Don Grelecki
Dear Don,
Chicago climate records peg the average date of the city’s first 90-degree day
around May 29 based on 80 years of data from Midway Airport. The earliest 90-
degree day ever recorded here occurred back-to- back on April 10-11, 1930.
In 1875, there were no 90s at all, the only year the city failed to reach that
benchmark, according to other records.
Last year Chicago recorded its first 90-degree day on May 14 and in 2006
it occurred on May 28.
Days with highs in the 100s here are not as common. Our last 100-degree
day was July 24, 2005, when the thermometer officially peaked at 102
degrees. Recent highs in the 100s occurred in 1999 and in 1995, when a deadly
heat wave caused more than 750 fatalities.

Posted by wgnweather at 10:01 PM | Permalink

Dear Tom,
A friend in Iraq has told me that, besides a lot of heat and dust, they had a lightning
storm—no rain, no thunder—just lightning. How can you have lightning and no
thunder?

Mary Abuja, San Diego

Dear Mary,

Thunder is always a by-product of lightning, but sometimes we are too far away to
hear it.

A lightning spark can heat the air through which it passes to 54,000 degrees
practically instantaneously. Such extreme heating causes air to expand explosively,
followed immediately by cooling and rapid contraction. That physical process sets up
sound waves that blast outward, and we hear them as thunder.

However, thunder dampens quickly as it spreads and it rarely carries more than 15
miles from its source, whereas lightning bolts are often visible at distances beyond
50 miles if intervening clouds are not present.

Posted by wgnweather at 10:35 PM | Permalink | TrackBacks (0)

Dear Tom,
When can I be assured the danger of frost and freezing
temperatures in Chicago is past for good?
Jeffrey Rayner, Chicago

Dear Jeffrey,

Light frost can form on plant leaves on a clear, calm night even when air
temperatures a few feet above the ground are as high as 38 degrees. A heavy, killing
frost usually requires a temperature of 32 or lower.

Because overnight temperatures on any given chilly spring night can, in
extreme cases, vary by 20 degrees across the Chicago area, it is difficult to pin down
an exact date. It really depends on your location.

Here are some guidelines: Near the lake, light frost (38 degrees) has never occurred
beyond May 31; heavy frost (32) never beyond May 14. Within about 2-6 miles inland,
the corresponding dates are June 4 and May 13; 7-15 miles inland, June 22 and May
29; farther inland, add seven days.

Posted by wgnweather at 9:28 PM | Permalink | TrackBacks (0)

Dear Mr. Skilling,

How can a rainstorm or snowstorm travel thousands of miles, constantly depositing
moisture but never running out of it? Why does it not eventually lose steam and dry
up?
John H. Deppen, Portage, Mich.

Dear John,

Your questions rank high among the issues that weather forecasters contend with on
a daily basis. The precipitation-producing capability of a storm system changes
constantly—increasing, decreasing, sometimes ceasing.

The reasons are complex, but one factor stands out: Low-level winds, especially
southerly winds in advance of a low pressure system, constantly deliver "new air" to a
storm system as it moves along. If the moisture content of that new air varies, as it
usually does depending on its source region (like the Gulf of Mexico), the
precipitation capability of the storm system will also vary.

Posted by wgnweather at 9:52 PM | Permalink | TrackBacks (0)

Dear Tom,
Why are severe thunderstorm warnings are never issued for lightning?
Jim Froemke, Chicago

The National Weather Service issues a severe thunderstorm warning when it believes
a storm will produce winds of at least 58 m.p.h. and/or hail at least three-quarters
inch in diameter or larger. Lightning ground strikes are not severe thunderstorm
criteria.

Meteorologist Rusty Kapela at the Milwaukee NWS says, "Any convective cloud that
manages to generate one lightning bolt is, by definition, a thunderstorm. If lightning
were a criterion, even a weak thunderstorm such as a garden-variety thundershower
would require the issuance of a warning."

That would greatly diminish the effectiveness of the warnings. Kapela advises that
any thunderstorm should be considered severe with respect to lightning.

Posted by wgnweather at 9:41 PM | Permalink | TrackBacks (0)

Dear Tom,
How rare is it for Chicago to receive snow in May?
—Gladys Reynolds
Dear Gladys,
Snow during May in Chicago is not as rare as you might think. The city’s May snow
records date to 1885, and in those 123 Mays, snow has been recorded in 31 of them, a
frequency of once every four years. Of course, the vast majority of those May snows
were insignificant. But over the years the city has experienced a few noteworthy May
snows. In 1940 the city was surprised by a 2.2-inch snowfall on May 1-2 with some
northwest suburbs receiving as much as 5 inches. On May 3, 1907, 1.3 inches of snow
was logged. The city’s latest measurable May snow took place on May 11, 1966, when
0.2 inches fell. Chicago’s most recent encounter with snow in May took place three
years ago, when a trace was reported on May 2, 2005.

Posted by wgnweather at 10:10 PM | Permalink

Dear Tom,
There is a family story that says my grandmother melted snow to give my aunt her
first bath. She was born Downstate in Flora, Ill., about halfway between St. Louis and
Vincennes, Ind.., on June 12, 1936. Could this be true?
Nancy Miller, Dyer, Ind.
Dear Nancy,
We are certain it did not snow in Flora, Ill., during June 1936, but we think we
may have found the basis of your family’s story. June 1936 was a hot month in
southern Illinois, with high temperatures reaching the 90s and low 100s on many
days, though on the date of your aunt’s birth the high was only 81 degrees. Flora was
hit by several thunderstorms that month, including some that produced hail and
damaging winds. One of these storms occurred on June 22, battering the area with
hail and 0.8 inches of rain. It is possible your grandmother collected and melted the
hail to give her 10-day-old daughter a bath.

Posted by wgnweather at 8:24 PM | Permalink | TrackBacks (0)

Dear Tom,
I remember a very warm late April in Chicago when I was a boy in the early 1960s. Can
you tell me what year that was?
Robert Klein
Dear Robert,
We believe the period you remember occurred during late April 1962. After two warm
days in the lower 70s in March, April opened on a cool note, with the high temperature
reaching only the lower 40s on April 1 and 2. The month remained cool for the first
three weeks. Warm weather finally moved into the area April 20, when the mercury
soared to 80 degrees and remained entrenched for the rest of the month. The
temperature climbed to a summerlike 86 degrees April 25, followed by highs of 88 and
86 the next two days as persistent southwest winds pumped very warm air into the city.
After a two-day cool-down to around 70, readings surged back to a steamy 88 degrees
on the last day of the month.

Posted by wgnweather at 11:14 PM | Permalink

Dear Tom,
What is the difference between a "small tornado" and a "microburst"?
Paul Dunn, Bloomington, Ill.
Dear Paul,
A microburst is an area of strong and often damaging winds that occurs when rain-
chilled air, cooler and therefore heavier than its warmer surroundings,
surges down through a thunderstorm, then "splashes" violently outward when
it encounters the ground. By definition, a microburst affects an area less
than 2.5 miles in diameter.

Microburst winds, though limited in extent, can be strong. On June 29, 1990,
a microburst in Streamwood generated 150 m.p.h. winds that killed a person.

A tornado is a violently rotating column of air than extends from the base of a
thunderstorm down to the ground. The air within a tornado spirals upward in a
corkscrew fashion at speeds typically 100 to 300 m.p.h.

Posted by wgnweather at 9:29 PM | Permalink | TrackBacks (0)

Dear Tom,
My job requires me to fly often. I have noticed that the "takeoff time"—the time
elapsed between when takeoff power is first applied and when the jet finally lifts off
—is greater during hot, humid weather. What is the explanation?
William Frederick

Dear William,
Air density is the issue. The wings of an aircraft generate lift that is

proportional to the density of the air through which the craft is flying, as well as its
forward speed. Reduce one and you must increase the other in order to compensate.

When attempting a takeoff in less-dense air, the pilot must bring the craft to a
greater speed to attain lift sufficient to get the craft airborne. This takes more time
on the runway.

Weather conditions that reduce air density are precisely the factors that you have
noticed: heat and humidity. Hot air is less dense than cold air and, although it seems
counter-intuitive, humid air is less dense than dry air.

Posted by wgnweather at 9:31 PM | Permalink | TrackBacks (0)

Dear Tom,

Why was the moon shining blood red on the night of Sunday night?

Ken Boncela, Naperville, Ill

Dear Ken,

Many readers commented on the haunting shades of red and orange that the moon
displayed Sunday evening.

The moon does not generate any color of its own, but only reflects sunlight. Lunar
colors on Earth are a measure of our atmospheric clarity as moonlight passes through
it. Like sunlight, the atmosphere scatters the shorter wavelengths of moonlight,
leaving shades of red, orange and yellow. These colors are pronounced when the
moon is near the horizon and its light has to penetrate a greater distance of the
atmosphere. As the moon rises higher, the red/orange hues fade.

Because cloud-free, moonlit nights are often a result of high pressure, colors are
enhanced by haze or dust trapped under a high pressure’s inversion. On rare
occasions, warm colors are replaced by blue tints, a result of smoke from distant
forest fires.

Posted by wgnweather at 9:39 PM | Permalink | TrackBacks (0)

Dear Tom,
What is the earliest date that Chicago has ever reached 90 degrees?
—Wayne Griffin
Dear Wayne,
Chicago’s earliest hot weather occurred nearly 80 years ago, with highs of 90 degrees
on April 10-11, 1930. Just two days earlier, with high pressure over the area, the
mercury dipped to 34 degrees. As the high moved east, strengthening southwest winds
delivered a flood of warm air. The mercury jumped to 70 on April 9, then soared to the
two record early-season 90s. Since 1871, the city has reached the 90-degree hot
weather benchmark only four times in April. The other two occurrences were a high of
90 degrees on April 30, 1942, and a 91 on April 22, 1980. The 1980 high of 91 was
notable because just a week earlier, the city was hit with nearly 4 inches of snow on
April 14-15, a testament to the huge temperature fluctuations Chicago can experience
in the spring.

Posted by wgnweather at 9:44 PM | Permalink

Dear Tom,
Chicago’s temperatures are sometimes higher at night than during the day. How often
does this reversal of the normal temperature cycle occur?
—Thomas Rhiner
Dear Thomas,
Daily high and low temperatures are defined as the maximum and minimum that occur
during the 24-hour calendar day, local standard time. During the winter, Chicago’s
daily high occurs between 1 and 4 p.m. on 40 percent of the days. In the summer, the
percentage rises to 65 percent. On 13 percent of the days (one day in eight) the high
occurs about midnight. Frequently in winter, during a warm-up after a cold spell,
temperatures will continuously rise, with the day’s high being reached at midnight. Or
if a strong cold front passes the previous night, the day’s high will come at midnight at
the beginning of the calendar day, with temperatures falling the rest of the day.

Posted by wgnweather at 10:30 PM | Permalink

Dear Tom,
When did the science of meteorology begin? Can you give an approximate year?
Fred Fredericks, Belle Plaine, Iowa
Dear Fred,
The earliest documents about weather, preserved on fragments of papyrus and clay, come
to us from ancient Egypt and Babylonia, and date from about 2500-2000 B.C. At about the
same time, ancient Chinese scholars had begun keeping descriptive weather journals by
about 2200 B.C., and during the Shang Dynasty in 1600 B.C., scholars attempted to
analyze weather in 10-day blocks. Later, in ancient Greece, Aristotle formalized the study
in his “Meteorologica” (340 B.C.). As you might suspect, the term “meteorology” comes to
us from Aristotle’s work. At the time, a “meteor” referred to hail, rain, clouds,
rainbows—basically any substance suspended in the air or that fell from the sky.

Posted by wgnweather at 11:09 PM | Permalink

Dear Tom,

Spring means more thunderstorms and that always causes controversy at outdoor
sports events like baseball and soccer. I maintain that such events should be stopped
as soon as thunder is heard, but many disagree with me. What is your opinion?

Samuel Widder

Dear Samuel,

I will defer to the experts on this one, and without exception they all say that outdoor
activities should cease immediately when thunder is heard. Thunder is a by-product of
lightning and if thunder is heard, lighting is also present.

Brian Bennett, a principal author of the NCAA's official lightning safety rules, says
thunder should prompt an orderly evacuation of the field and that the refuge of a safe
shelter should be sought. Furthermore, he recommends that outdoor activities not be
resumed until 30 minutes after the last rumble of thunder. It's unfortunate, but
lightning safety is very inconvenient.

Posted by wgnweather at 9:47 PM | Permalink | TrackBacks (0)

Dear Tom,
My parents gave me a picture that was taken on our farm in Manteno, Ill. after a mid-
April 1961 snowstorm. Do you have any record of this storm?

Janet Sorensen, Wilmington, Ill.

Dear Janet,
Your picture, which has been posted on our weather blog at www.wgntv.com, was
taken after one of the heaviest late-season snowstorms to ever hit northeast Illinois.
The storm began late April 15 and continued into the early morning hours of April
17, bringing the area 5-8 inches of heavy, wet snow. Strong winds piled the snow
into 6 foot high drifts. The Chicago area measured 6.8 inches of snow while south of
the city near Manteno, Kankakee received 5.6 inches. Like all late-season snows, this
one did not last long. Temperatures quickly rebounded into the 60s and 70s and the
snow was gone in a day or two.

Posted by wgnweather at 9:30 PM | Permalink | TrackBacks (0)

Dear Tom,
What kind of spring did Chicago experience in 1967
prior to the Oak Lawn tornado?
Veronica Michaels

Dear Veronica,
The Oak Lawn tornado, the deadliest to ever hit the Chicago area, killed 33 people as
it raced through that southwest suburb on Friday evening, April 21, 1967. Before the
tornado, the city had been experiencing a typical spring.

March remained chilly until the middle of the month, when the last vestiges of
January’s paralyzing 23-inch “Big Snow” finally melted. March closed with several
days in the 60s and 70s. The mild weather continued through mid-April, with eight
more days in the 70s, including a 74- degree high on the day of the tornado. The
weather turned cold in the wake of the twister. Three inches of snow blanketed the
city on April 23, followed by the city’s first below freezing temperatures since March 22.

Posted by wgnweather at 9:25 PM | Permalink | TrackBacks (0)

Dear Tom,

Why do the sun and moon look larger as they rise and set and are close to the
ground?

Barry Baxter, Ottawa, Ill.

Dear Barry,
Both the sun and moon seem to be larger when they are positioned near the horizon,
but it is entirely an illusion.

It's such a compelling illusion, though, that it has a name: the "moon illusion."

No single explanation sufficiently accounts for the illusion, but it probably results
from the varying ways our minds relate the size and distance of the sun and moon
when they are viewed by themselves (high in the sky) or against a backdrop of other
objects (near the horizon). The sky at the horizon seems more distant than the sky
overhead. When viewed against the "more distant" horizon sky, the sun and moon
appear larger than when seen against the "closer" overhead sky.

Posted by wgnweather at 9:21 PM | Permalink | TrackBacks (0)

Dear Tom,
When I was a kid, we couldn't count all the stars in the sky. Now I have to look hard to
see one. How come the change?
—J. Roberts, Batavia
Dear J. Roberts,
Triton College astronomer Dan Joyce says you can blame metropolitan lighting. Here's
Joyce's answer: "Back in 1978, I sent a 'real telescope' to 'Star Wars' creator George
Lucas, claiming that with it he could detect galaxies over 300 million lightyears away.
But it was with a caveat: I warned him that proximity to city lights would spoil the view.
"Imagine the disappointment of those of us in astronomy who seek to show off the
marvels of the cosmos, understanding that the galactic light has traversed space so
vast, only to be obscured in the last fifty-thousandth of a second as it encounters the
glare of metropolitan lighting wasted on the night sky."

Posted by wgnweather at 10:04 PM | Permalink

Dear Tom,
I read a book about the 1930s Dust Bowl, “The Worst Hard Time.”
It mentions a dust storm that impacted Chicago.
What exactly happened here?
—Mike Rehor

Dear Mike,

During the 1930s, Chicago along with the Plains and Midwest were in the
grasp of a combination of heat and drought known as the “Dust Bowl.” These
summers were characterized by searing heat and blowing dust, and it was
during this period that Chicago recorded many of its highest temperatures.
The dust storm of May 10-11, 1934, was remarkable. With northwest winds
gusting to more than 50 m.p.h. and relative humidity levels at a record low
13 percent, clouds of dust swept into Chicago, reducing the Visibility to
less than one mile in many areas. Officially, seven days in the 90s were
logged in May 1934 including a scorching 98 degree high on May 31.

Posted by wgnweather at 7:42 PM | Permalink | TrackBacks (0)

Dear Tom,
How can animals detect weather before something happens?
Paul See, Schaumburg
Dear Paul,
Your question is representative of many that we receive concerning the ability of
animals to predict the weather. But contrary to popular belief, there is no documented
evidence that animals have that ability. Authorities from a range of disciplines agree
that animal behavior, even when it is uncharacteristic, is a response to past or current
weather, or the r