ASK TOM WHY: March 2009 Archives

Dear Tom,
Does Hawaii have a tsunami season?
Bill Jahn
Dear Bill,
Tsunamis are an ever-present danger on the ocean coasts of the Hawaiian Islands and
around the entire Pacific Basin, but there is no such thing as a "tsunami season" does
because tsunamis are not weather-related.

Tsunamis are sea waves caused generally by earthquakes, less commonly by submarine
landslides or massive landslides into the ocean, and infrequently by submarine volcanic
eruptions. Those phenomena are geologic in nature and occur randomly, not
seasonally.

On average, the Pacific Basin experiences a destructive tsunami about every seven
years, but none has occurred in 34 years. Oceanographer and tsunami expert Dr. Walter
Dudley has said, "We will soon have approached the longest period in recorded history
without a Pacific-wide tsunami, so one could say we're due now."

Dear Tom,
Could our nation's 200th birthday- July 4, 1976 been a day without precipitation
anywhere in the country? I seem to remember no adverse weather. Can you check it out?
Ge Breu

Dear Ge,
Though sprawling high pressure brought much of the nation beautiful weather on its
bicentennial, there was still plenty of rain. Showers and thunderstorms fell from eastern
New Mexico to the Carolinas, then north to New York. Rain was heavy in many areas,
with 1-inch plus totals in Alabama, Georgia and Tennessee.

Severe thunderstorms produced damaging winds in Georgia, and least five tornadoes
were reported, three in Texas and one in Wyoming and Colorado. Light showers also
dampened the Pacific Northwest. Rain-free periods across the entire lower 48 are
extremely rare and would last only for a few hours--not an entire day.

Dear Tom,
The name "Alberta Clipper" denotes both origin and speed of the storm. Are
there any other names for northerly storm systems that affect Chicago? What
about systems that arrive courtesy of our southern neighbors?
Mark Welch, Tinley Park
Dear Mark,
In addition to "Alberta Clippers," fast-moving snowstorms that originate a
bit farther east in Canada have been dubbed "Saskatchewan Screamers." A
persistent cross-polar jet stream bringing a parade of frigid arctic high
pressure systems to the Midwest is often called the "Siberian Express." As
far as systems originating in warmer areas, a winter pattern that brings
mild but stormy weather from the Pacific to the West Coast and Alaska is
called the "Pineapple Express." Snowstorms that develop in the
Texas/Oklahoma region are referred to as "Panhandle Hooks," and those that
develop in the lower Mississippi Valley sometimes carry the name "Louisiana
or Mississippi Rebel."

Dear Tom,
Right after a March 22 high near 80 degrees at Rapid City, S.D., a blizzard brought up to
30 inches of snow. What is the warmest Chicago has been before a major snow?
Martin Shanahan Jr., Joliet

Dear Martin,

The Chicago area basked in record 65-degree warmth on Jan. 24, 1967; two days later
the city was shut down by its biggest snowstorm, the 23-inch Big Snow of Jan. 26-27.
To this day, many Chicagoans become apprehensive when unseasonable winter warmth
invades the city. Since 1885, the city has recorded half a dozen 6-inch-plus
snowstorms that have developed within three days of high temperatures of at least 60
degrees, and an additional 10 major snows that have closely followed days with highs
in the 50s. The large variations in temperature are indicative of a volatile atmosphere,
ripe for major storm development.

Dear Tom,
My mother always told a story about our family moving during a blizzard on
my first birthday on March 26, 1944. How much snow actually fell that day?
George Pratl, Willowbrook
Dear George,
I'm sure the snow put a crimp into your family's move, but the snowfall that
day was hardly the "storm of the century." The record books show that just
2 inches of snow fell that day, and combined with the 1.7 inches from the
previous day's snowfall, the city received a two-day total of 3.7 inches.
Temperatures were in the middle 30s that day, and there was some rain mixed
with the snow, so the streets were probably a slushy mess. Just two days
earlier on March 24, spring was in the air and the mercury reached a balmy
65 degrees. However, in typical Chicago spring fashion, a cold front passed
and temperatures plunged, setting the stage for the ill-timed moving-day
snowfall.

Dear Tom,
Has there ever been an April in Chicago that did not register an 80 degree
or higher day?
--James L. Stewart

Dear James,
April usually brings Chicago its first really warm spring weather, but only a
little more than half of the April's here since 1871 have registered an 80
degree or higher temperature. Climatologist Frank Wachowski checked the
record books and found that 77 of the 138 Aprils (56 percent) since 1871 have
recorded 80 degree or higher temperatures. April 1977 holds the record for the
most, with eight, followed by 1915, with seven, and 1896, with six.
The last April failing to reach 80 degrees was in 2000.

Chicago has also recorded some 80 degree temperatures in March. The city's earliest
was an 80 degree high logged on March 3, 1974, and Chicago's warmest March day was
March 29, 1986 when the mercury spiked to 88.

Dear Tom,
What are the strongest winds we've ever had in the Chicago area?
Bob Klicpera Romeoville

Dear Bob,
Officially the windiest day in the Chicago area occurred more than a century ago on
February 12, 1894. On that day a raging blizzard not only brought more than 10 inches
of snow to the city, but the ferocious northeast winds that accompanied it piling the
snow into huge drifts, also produced the city's all-time official highest wind of 87
m.p.h. Of course the area has been frequently blasted by strong wind gusts during
severe thunderstorms. On August 26, 1965 Midway Airport measured a record wind
gust to 88 m.p.h. and at O'Hare a wind gust reached 84 m.p.h. during a severe
thunderstorm on March 27, 1991. Throughout the years thunderstorm wind gusts
approaching 100 m.p.h. have been reported throughout the metropolitan area but are
not considered to be official.

Dear Tom,
Although it is said that in Chicago we cannot produce vitamin D from exposure to the
sun during October through April, I sometimes wonder. I have read conflicting reports.
Laurie Black

Dear Laurie,
Oak Park dermatologist Dr. Bryan Schultz tells us that exposure to 5 to 10 minutes of
sunlight (ultraviolet light) in the summer will produce adequate vitamin D in light-skin,
but up to five times as much exposure is required for dark skin.
However, Schultz explains that Chicago's sunlight "... is not usually adequate from late
fall to early spring, thus increasing one's risk for deficiency in the winter. Milk, fortified
juice and salmon are on the very short list of foods supplying vitamin D, so a
multivitamin with 400 I.U. (800-1000 I.U. for older adults) can help, in addition to
allowing one to reduce the aging and carcinogenic effects of UV by using sunscreen."

Dear Tom,
I recall an Easter, I think in March 1965, with at least 8 inches of snow.
Can you confirm and provide some details?
Maryellen Shute
Dear Maryellen,
The Easter that you remember did not occur in 1965, but one year earlier on
March 29, 1964. That Easter remains the city's snowiest on record with
officially 7.1 inches of snow on the books. The snow began falling shortly
before sunrise and continued through late afternoon. Strong winds gusting as
high as 37 m.p.h. reduced the visibility to near zero and piled the snow
into large drifts. Motorists were stranded in the near blizzard conditions
as traffic slowed to a crawl. It was a very cold day for late March with a
high of 29 degrees and a low of 18. The city's second snowiest Easter took
place back in 1920 when 6.4 inches of snow fell on April 4.

Dear Tom,
When is the sun the closest to Illinois? I have a bet with my husband and he
believes everything you say!
Cheryl Hanson
Dear Cheryl,
The Earth completes an orbit of the sun in approximately 365.24 days, but
the path is not perfectly circular. Rather, it's an ellipse -- a slightly
flattened circle -- and the sun is not quite in the center of the elliptical
area. The Earth (and Illinois) is consequently closest to the sun when it
travels through the "end point" of its elliptical path that lies nearest the
sun; it is farthest from the sun at the opposite "end" of the ellipse.
Those points are known as perihelion (closest to the sun) and aphelion
(farthest). Perihelion and aphelion dates vary by a few days from year to
year, but in 2009 perihelion (91.7 million miles) occurred at 9 a.m. CST on
Jan. 4 and aphelion (94.8 million miles) will occur at 9 p.m. CDT on July 3.

Dear Tom,
I was curious: How many days in the 138 years of records have had the same high and
low for a given day.
Cole Turgeon, Brookfield

Dear Cole,
Such days are rare, but they do occur. A computer sweep of Chicago's official
temperature data base from Nov. 1, 1870, through Dec. 31, 2008--that’s 50,465
days--reveals only three days on which temperatures remained absolutely steady
through the entire 24-hour day: March 13, 1878, when the city's official thermometer
registered a constant 44 degrees; March 24, 1891, with 32; and Feb. 6, 1942, with 35.
The range between the city's maximum and minimum temperatures was only 1 degree
on an additional 24 days, most recently six years ago on April 8, 2003, when the high
and low temperatures were 32 and 31 degrees.

Dear Tom,
Is rainwater safe to drink? I've heard that it is pure, but I wonder about
it.
John Koldinger
Dear John,
We receive this question frequently, and your skepticism is warranted. Even
ignoring the effect of atmospheric pollution, meteorologist and former
Chicagoan Dr. Keith Heidorn tells us it is a misconception that raindrops
are pure.
Referring to condensation nuclei, Heidorn says, "The fact is, rain would not
fall without some degree of impurity in the air to act as a seed. This seed
may be a chemical salt, an acid droplet, a speck of dust or soil, or even a
bacterium."
Consider also that every cloud droplet begins as moisture condensing onto a
tiny airborne "nucleus." Because a raindrop might consist of a million or
more individual cloud droplets, it is likely that each raindrop contains the
material from a million or more condensation nuclei.

Dear Tom,
A recent column referred to a tornado that hit Chicago near O'Hare Airport. I was in
school then and remember a warning being issued. Can you provide some details?
Sam Schaumburg, Ill.

Dear Sam,
March 12, 1976, was an active severe weather day with four F2 or stronger twisters
touching down in northeast Illinois and northwest Indiana. The twister near O'Hare had
a 17 mile-long intermittent path that stretched from Northlake to Wilmette. The F2
storm killed two, injured 66 and inflicted heavy damage to an industrial park near the
airport. It also damaged buildings near Cumberland and Higgins Road.

This twister made national headlines when it passed within one-quarter mile of
President Gerald Ford's motorcade, who was in town campaigning for the upcoming
Presidential Election.

Dear Tom,
I recall the spring of 1977 being one of the warmest in memory. Was it?
John Zang Bolingbrook

Dear John,
Chicago's spring in 1977, with an average temperature of 56.2 degrees, was by far the
city's warmest, beating out runner-up, spring of 1921, by 2.3 degrees. Most
Chicagoans welcomed spring 1977 with open arms because it followed the very severe
winter that featured 54.1 inches of snow, 23 days of zero or below temperatures and a
record 43 consecutive days below freezing. Spring, 1977 brought some unbelievable
early-season warm spells. March logged 13 days in the 60s and 70s and April
registered eight days in the 80s. However, it was a May heat wave that really turned
heads. For nearly two weeks from May 13 to 25, daily high temperatures reached 86
degrees or higher, including nine straight days with highs in the 90s.

Dear Tom,
Many Chicagoans firmly believe that a tornado cannot touch down in the city. That's
not true, is it?
Scott Robertson, Chicago

Dear Scott,

No it is not! Tornadoes do hit within the city. At least a dozen tornadoes have been
documented in Chicago, though many have been weak. Only one has been recorded
downtown--an F3 storm that swept from near 18th Street and the Chicago River to the
current site of Navy Pier on May 6, 1876.

On March 12, 1976, an F2 twister clipped the far northwest side near O'Hare and on
March 4, 1961 an F2 tornado killed one and injured 115 as it cut across the South Side.
The tail end of the F4 Oak Lawn tornado on April 21, 1967 traveled across the South
Side before dissipating over the lake near 79th Street. Chicago's earliest recorded
tornado struck the Norwood Park area on May 22, 1855.

Dear Tom,
I want to put my snow blower away for the season. What are the chances of a heavy
snow in March or April?
Mike Hunnicutt Woodridge, Ill.

Dear Mike,

You can put your snow blower away, but don't be surprised if you have to do some
shoveling. In Chicago, late season snowfalls tend to be heavy and wet, "heart-attack"
snows. Even though the average date of the city's last 1-inch-plus snowfall is March
20, some of the city's biggest snows have occurred after that date, including 19.2
inches March 25-26, 1930 and 10-11 inches April 2-3, 1975. In 1970 Chicago was
rocked by two late-season snows--14.3 inches fell March 25-26 with an additional
10.7 inches falling April 1-2. Chicago's latest major snow was a 6.8 inches April 15-17,
1961; so it is a good idea not to put your snow blower away until you file your income
taxes on April 15.

Dear Tom,
It's not wise to take shelter under a tree or swim in open water during a
thunderstorm. Is it okay to take a shower in one's house under the same
circumstances, or is that also not advisable?
Joe Bednar, Downers Grove
Dear Joe,
In very rare cases, the electric charge from a lightning strike to or near a
house will transfer along a conducting path (such as copper plumbing pipes)
to the interior of a house. For that reason, showering or bathing is
discouraged while a thunderstorm is in progress and for a half hour
afterward.
That's the word from Richard Kithil, president and CEO of the National
Lightning Safety Institute (NLSI). Kithil comments that NLSI has uncovered
no reports of deaths or injuries in those situations, but he adds that "the
absence of evidence is not evidence of absence." Common sense, caution and
prudence is therefore advised.

Dear Tom,
While lying in bed recently, I had a south-facing window open about an inch and could
feel cold air coming into the bedroom. I wondered if warm air from inside was leaving at
the same rate. There was no wind blowing the air in and the bedroom door was closed so
there really was no cross ventilation.
Dan Oshea, Oak Lawn

Dear Dan,
Air moves in response to differences in air pressure, always moving from higher to lower
pressure. The driving force is known as the pressure gradient force and it absolutely
controls air movement. Other things being equal, the internal pressure in cold air is
greater than in warm air, and so cold air will always try to undercut warm air. The
American Society of Heating, Refrigerating and Air-Conditioning Engineers assures us
that warm air exiting your bedroom balances the cold air entering it through the open
window.

Dear Tom,
When was Chicago's coldest winter and what has been its coldest month?
David J. Nennich
Dear David,
Chicago's coldest winter occurred more than a century ago during 1903-04
when the December-February period averaged just 18.3 degrees, fending off
the winter of 1978-79 by a scant 0.1 degrees. The winter of 1903-04 was not
only cold, but very snowy with 59.5 inches of snow falling. The ground was
continuously snow covered for 56 straight days, and the winter's deepest
snowpack reached 10 inches. During that winter the city logged 17 days with
temperatures of zero or below with the season's lowest reading falling to
minus 15. The city experienced its all-time coldest month in January 1977,
which averaged only 10.1 degrees. The mercury never broke freezing that
month (30 degrees was the month's highest) and fell to zero or below on 17
of the 31 days.

Dear Tom,
Spring is almost here and that means Chicago's lake-breeze season is about to begin.
How far inland does the lake breeze typically reach?

William P., Lindenhurst, Ill.

Dear William,

In the "old days" -- that is, prior to the early 1990s when the National Weather Service's
Doppler radar became operational in Romeoville--28 miles southwest of the Loop --
area meteorologists could not locate the position of the lake-breeze front with
precision. Now, however, the powerful Doppler radar reveals the inland penetration of
the lake breeze quite clearly.

Meteorologist Mark Ratzer of the Chicago NWS tells us that it's a mixed and highly
variable bag. On some days the lake breeze front lies only a few hundred feet from the
lake shore, but on other days it surges 40 miles inland and can deliver lake-cooled air
to the entire metropolitan area. Its inland penetration is very difficult to anticipate.

Dear Tom,
What is the chance that we won't have any more troublesome snow storms this winter
-- say two inches or more?
Terry Vance

Dear Terry,

The portion of the year during which Chicago can experience snow extends well into
the spring, but history tells us the city's snow season winds down in March. The
likelihood of another significant snow storm is diminishing with every passing day --
but history also cautions that it would be premature to put away the snow shovel just
yet.

Late-season snowstorms occur at relatively high temperatures, tend to occur in a
moisture-laden environment and produce heavy, slushy snow that is colloquially
known as "heart-attack snow." The probability of a snow of 2.0 inches or more from
this date forward stands at 46 percent, and it does not diminish to 0 percent until May
2. Chicago logged. 3.7 inches of snow on May 1-2, 1940, its latest-ever 2-inch snow.

Dear Tom,
Why is the Lake Michigan water temperature reported this time of the year?
Doug Bober

Dear Doug,

While the lake water temperature is obviously an important consideration for
swimmers during the summer, it additionally provides valuable information
the rest of the year. A lake that is warmer than normal during late fall or
early winter may well spare the city from a major snowstorm by keeping the
precipitation as rain.

A knowledge of lake temperatures allows forecasters to determine if cold
outbreaks will produce lake-effect precipitation, and whether it will be
rain or snow. Marine interests can gauge when ice formation will begin as
water temperatures slide toward 32 degrees. Finally, lake temperatures
influence the degree of warming or cooling to be expected when onshore winds
prevail -- especially helpful when predicting fog or glazing for areas near
the lake.

Dear Tom,
Glaciers move, but glacial ice starts as snow. How much snow has to fall before it
becomes moving ice?
Shawn Coren

Dear Shawn,

Meteorologist Anton Kapela of the Milwaukee Weather Forecast Office spent three
months in Antarctica in 1976 and he tells us, "Once snow reaches a depth of 60 feet, its
structure changes such that the crystals re-align themselves (due to internal pressure)
into layers, and that allows slippage. Once the snow depth reaches 90-100 feet, gravity
becomes a factor. The ice starts to move and a glacier has been born!"

How much snow does it take to make 100 feet of ice? Assume a glacier is composed of
snow that had a snow-to-meltwater ratio of 20:1 when it fell. It would therefore require
at least 1,847 feet of snow (because one foot of water produces 1.083 feet of ice) to
compress into the minimum necessary depth of ice to form a glacier.

Dear Tom,
Snow is measured in tenths of an inch, but how can they measure rain, which is reported in hundredths of an inch, in such tiny increments?
Scott Burgess, Chicago
Dear Scott,
Measuring snow depth is straightforward: Use a ruler graduated in tenths (0.1) of an inch and find a representative snow depth. Rain is a different matter because, as you suggest, one hundredth (0.01) inch of water is too thin a depth to be measured directly.
A standard rain gauge utilizes the principle of multiplication. Rainwater drains via a funnel from a collection area (typically a circular area eight inches in diameter) into an accumulation tube whose area is only one-tenth as great. Every hundredth of an inch of rain from the collection area therefore stands 10 times as deep, or one-tenth inch deep, in the accumulation tube. A ruler graduated to tenths of an inch is then used to measure the depth of the water.

Dear Tom,
Considering Chicago's daily record high and record low temperatures, what day has had
the greatest spread? For example, on Jan. 1 the record high was 65 degrees and the
record low was 10 below zero for a spread of 75 degrees.
--John Foley, Evanston

Dear John,
We took a look at Chicago's daily temperature records for each of the 365 days in the year
and found that Jan. 20 logged the greatest spread between the highest and lowest
temperatures ever observed on any given day: a range of 90 degrees from the day's record
high of 63 degrees (in 1906) to 27 degrees below zero (in 1985). Incidentally, that subzero
temperature stands as the lowest reading ever officially recorded in Chicago since the
inception of temperature records 138 years ago. Many area residents have vivid memories
of that day in which the windchill touched 77 degrees below zero.

Dear Tom,
What is the origin of the expression, "I'm feeling under the weather"?
Paul Sarewich, Chicago
Dear Paul,
Like many phrases, a precise and undisputed origin of "I'm feeling under the
weather" may be lost in the mists of the past, but we were able to uncover
two compelling answers to your question. The "Facts on File Encyclopedia of
Word and Phrase Origins" by Robert Hendrickson credits the first use of
"under the weather" to American author Donald Grant Mitchell (1822-1908)
(a.k.a. Ik Marvel) in the book, "Reveries of a Bachelor."
"Salty Dog Talk: The Nautical Origins of Everyday Expressions" by Bill
Beavis and Richard G. McCloskey offers another explanation. The phrase,
"under the weather bow" originally meant, in mariners' jargon, to feel
seasick. Those so afflicted were sent below deck, and the "weather bow" was
that part of the ship that took the brunt of waves during a storm.

Dear Tom,
We just experienced three straight below freezing days on March 1-3. What is the latest
in the spring that this has happened here?
Steve Billings, Chicago

Dear Steve,
We checked the record book with the help of climatologist Frank Wachowski and found
that the city's latest 3-day subfreezing snap was more than a century ago: April 1-3,
1899. During that period highs were just 27, 30 and 31 degrees. Strong high pressure
over the Plains and Rockies in conjunction with low pressure over New England kept a
brisk northerly flow of arctic air streaming across Chicago and the Midwest. That
early-spring cold snap came after the city shivered through an extended period of
record cold in February during which Chicago's temperature dropped as low as minus
21 degrees. Spring weather did return to the city after the early April freeze-out, with
readings climbing to a warm 80 degrees on April 13.

Dear Tom,
Who invented the word, "blizzard"?
Allan Standusky

Dear Allen,
The origin of the word "blizzard" is obscure. It first appeared in the United States 139
years ago and its first use was possibly on March 14, 1870, to describe a storm that
produced heavy snow and high winds in Minnesota.

Technically, a blizzard is an intense winter storm with sustained winds 35 m.p.h. or
higher and sufficient falling and/or blowing snow to reduce visibility below
one-quarter mile for at least three hours. Colloquially, the term is loosely applied to
any heavy snowstorm.

Blizzard conditions figured prominently in one of the worst-ever U.S. winter storms, the
"Storm of the Century" that raked the eastern quarter of the nation on March 13-14,
1993. It impacted 100 million people in 26 states from Florida to Maine, produced a
12-foot storm surge on Florida's west coast and 20-40 inches of snow and whiteouts
from Atlanta to Maine.

Dear Tom,
My boyfriend and I are having a disagreement on whether or not it is warmer near Lake
Michigan in Chicago. It seems that the temperature is typically higher toward the lake
than the outlying areas. Is this true, and if so, why?
Monica Johnson, Plainfield

Dear Monica,
It's usually true, but the explanation is complex because conflicting factors are
sometimes at work.

Cities, and especially large urban areas like metropolitan Chicago, are heat islands. The
central portion of a large urban area experiences higher temperatures--winter and
summer--than surrounding rural areas. That argues for a warmer city and cooler
suburbs, and that is the case most of the time.

But Chicagoland sprawls adjacent to Lake Michigan whose relatively mild waters warm
areas near the lake in the winter and whose relatively chilly waters cool areas near the
lake in the spring and summer.

Dear Tom,
Are weather forecasts becoming more accurate? Many years ago, forecasts only went
out two days.
Brenda Matsco

Dear Brenda,

Tremendous advances in computer technology (such as faster calculation speed and
more computer "memory") have led to a steady (and ongoing) improvement in the
reliability of weather forecasts.

Today's sophisticated mathematical simulations of the atmosphere -- the so-called
"computer models" -- are more accurate than ever. Armed with this guidance, weather
forecasters are producing better and better forecasts. The National Weather Service has
been verifying forecast accuracy since the 1960s and reports that the five-day forecast
of today is as reliable as the three-day forecast of the 1980s. Short-range forecasts
have improved by a day. That is, the Day 2 forecast of today is as accurate as the Day 1
forecast of yesteryear.

Dear Tom,
I have friends in the Los Angeles area and they are always complaining about
water shortages out there. Are they exaggerating?
Lewis Stinson
Dear Lewis,
Believe them. California is suffering through a long-standing drought (now
in its third consecutive year) and water shortages there are approaching
crisis levels. Gov. Arnold Schwarzenegger declared a state of emergency on
Feb. 27, an action that urges cities, towns and water agencies to reduce
water usage by 20 percent. Mandatory water rationing is an option if
conservation measures are insufficient.
The damage in California is staggering: Agricultural losses could reach $2.8
billion this year and 95,000 jobs are in jeopardy.
California derives much of its water from snow in the Sierra Nevada
Mountains, but the snowpack is presently at only 78 percent of normal.