April 2009 Archives

Chicagoans haven't endured a cloudier April in 14 years. Just 43 percent of the city's
possible sunshine was observed---short of the 53 percent considered typical. Nearly
half a foot of rain fell during the month, a good deal more than the 3.68 inch average.
Final April city precipitation tallies included 5.80 inches at Midway and 5.19 at O'Hare.
Precipitation fell measurably (0.01-inch or more water equivalent) on 14 of the month’s
30 days---the most of any April in 7 years. As frequent as that may seem, the tally is
actually quite close to the 138 year average of 12 measurably rainy days.

Year to date rainfall values continue to outpace the normal value of 9.71 inches in the
city. Midway Airport's 17.37-inch total remains the wettest in 81 years of observations
there. Other 2009 area totals include 14.94 at O'Hare, 16.80 Oak Brook, 14.67
Arlington Heights and 13.88 at St. Charles.

With the April’s close, two thirds of the three-month March through May meteorological
spring period is now behind us, and the city’s third-fastest warming month is
underway. Over the next 31 days, the city picks up an additional 57 minutes of daylight
propelling normal daytime highs from 64-degrees on the first to 75-degrees May 31.

Weekend wildcard here: Potential for Saturday night/Sunday rain

Saturday looks dry---but whether downstate rains reach a portion of the Chicago area
Saturday night into Sunday, is being monitored. While most computer forecast models
keep rains south, the predicted jet stream configuration is one which makes the Navy
NOGAPS model’s rainy prediction here over at least southern sections of the Chicago
area plausible. Stay tuned!

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Mr. Skilling,
We are learning about weather in first grade. What kind of clouds do we see the most?
Raquelle Blentlinger, Forest Glen School, Glen Ellyn, Ill.

Dear Raquelle,

Weather people have identified more than 70 different kinds of clouds, but they all fall
into three general groups that depend on the height of the cloud bases above the
ground. Those groups are low clouds (with bases below 6,000 feet), middle
clouds (6,000 to 18,000 feet) and high clouds (above 18,000 feet).

Most of the various kinds of clouds can be seen at one time or other in the Chicago
area, but the most common are the cumulus clouds--the flat-bottomed, puffy, "dob of
cotton" clouds seen on sunny days. Some cumulus clouds (like cumulonimbus -- the
thunderhead) build upward to 35 thousand feet or more but, with bases below 6,000
feet, are classed as low clouds.

John Hazzard, who farms near Wilmington in western Will County and always does such
a terrific job keeping us posted on conditions throughout the growing season, sends us
these shots of the standing water in what should be fully planted corn fields taken just
after lunch Tuesday. Area farmers have been unable to begin planting this year because
of all the rain and wet ground which has resulted. It’s a situation common across
Illinois and Indiana. John estimates it will take close to a week without rain for area
farmers to be able to get into these fields and points out yields begin dropping 2—3
bushels per acre May 15 and beyond. Even faster declines in yields occur beyond the
20th. Thanks for your thorough and always helpful updates, John—and for these
illustrative shots! Let’s hope for some extended dry weather—though models offer no
indication of an entire week rain-free anytime in the foreseeable future.

Tom Skilling

Photos courtesy of John Hazzard, Wilmington, Illinois

This tornado touched down near Cedar Hill, Texas, Wednesday evening and is captured
in these amazing photos by professional photographer David Mayhew, whose work is
always nothing short of spectacular. We’ve shared David’s work with you on this blog
and on WGN before. Cedar Hill is a small community near Floydada, which is roughly
50 miles northeast of Lubbock.
The Storm Prediction Center logged 12 tornado reports Thursday. David points out the
final photo includes TWO funnels! THANKS David! These are incredible shots!!

-Tom Skilling

Photos courtesy of David Mayhew, David Mayhew Photography, Chicago

A compact low pressure system lifting from Missouri into Chicago as April enters its
final day threatens the area with its second deluge in less than a week. Waves of
thundery downpours, capable of 1- to 2-inch rain tallies, could send sections of the
waterlogged Chicago area into flood before the storms scatter and diminish
mid-afternoon and beyond. The rainy onslaught continues the exceptionally wet trend
that has dominated this spring, generating more than a foot of rain (12.06 inches) since
March 1 at Midway---the heaviest total on record there for the period. Rainfall this spring
is nearly three times last spring's 4.34 inches.

With the ground so saturated, it’s estimated it could take five to six dry days before
many area farmers could get into their fields. But additional showers Thursday night
and potentially significant rains early next week show little sign of allowing such an
extended period without rain. Area farmers like to get corn planted by May 15 because
yields drop two to three bushels each day beyond that date.

The same system behind Thursday’s rain here swamped sections of Oklahoma and
Texas Wednesday—the site of devastating wildfires only two weeks ago. Four inches fell
at Altus, Okla., nearly 4 inches was recorded at Wichita Falls, Texas.

Interior Alaska's record-breaking 70s warmer than Chicago

Fairbanks, Alaska's Eielson Air Force Base---with a 73-degree high Wednesday---was
just one of many sites from interior Alaska east into Canada’s Yukon Territory to
establish new records for the date.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Has Chicago's average temperature changed through the years?
John Mannos Chicago

Dear John,
Chicago's long-term climate record that dates back to late 1870 is difficult to analyze
because of the numerous changes in the location of the city's official thermometer.

Through June 1942 readings were taken in an urban environment close to Lake
Michigan. From July, 1942 through mid-January 1980, the readings were logged at
Midway Airport, still an urban environment but not near the lake. Since then the official
site has been at O'Hare International Airport, a more rural, inland location. Despite all
these site variances, there has been little change. The city's earliest average
temperature, from 1871-1910 was 48.8 degrees and the most recent, from 1971-2000
is 49.1 degrees.

Wednesday offers a second day free of the downpours that have pushed rain tallies for
the spring season and for 2009 to date to the highest levels in 80 years--11.97 inches
and 16.78 inches respectively--based on observations at Midway Airport. Each total is
nearly twice the long-term average.

But the break in the rains isn’t likely to last long. Long-range computer projections
suggest four precipitation-generating systems could visit the Chicago area during the
next two weeks. A suite of two-week computer models puts total rainfall for that period
at 2 to 4 inches--well above the 1.68 inches that typically falls over 14 days this time of year.

The first of the four systems involves the same powerful front that shifted Chicago
winds northeast and slashed temperatures by more than 30 degrees along Lake
Michigan and 20 degrees inland between Monday and Tuesday. The front is predicted to
head north Wednesday night as the same moisture-laden air mass that set off 1-2-inch
rains late Monday over much of the metro area ignites new thunderstorms.

The development of a wave along that front may enhance rainfall Thursday--an
unwelcome development with rivers high and standing water already in parts of the
area.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Can you recommend a book or website where I could find precipitation totals
broken down by day for Chicago's Official readings at O'Hare, going back
about three years? I am a big fan of both your work and of meteorology
itself.
Mike O'Connor

Dear Mike,

We receive many requests -- too many to answer individually -- for Chicago's
official daily weather statistics from O'Hare International Airport. Those
data (temperatures, precipitation, snowfall and wind) are available from
1998 to the present, free of charge, on the Chicago National Weather Service
web site www.crh.noaa.gov/lot

Once there, follow these steps: search down the left side for Climate and click on word
"Local"; click on the button for "Preliminary Monthly Climate Data (CF6)" under the
header, "1. Product"; click on the button for "Archived Data", under the "3 timeframe"
header; select the desired month and year, then click "Go".

Chicago's first four-day string in 2009 with temperatures 70 degrees or higher arrived right on schedule--but came to an unceremonious end amid driving rains late Monday. Weather records show the average date of Chicago's first four consecutive days with readings of 70 or higher has come around April 29 in more than eight decades of weather records at Midway Airport. The warm-up has increased Lake Michigan surface water temperatures more 5 degrees in the past week.

By late Monday, downpours had pushed Midway's spring rain tally (since March 1) to 11.37 inches, making it the wettest meteorological spring on record to date in 81 years of weather observations at the South Side site. The total is nearly a half a foot (5.53 inches) higher than the long term average for the period (5.84 inches). With many rivers near bankful, Monday's cloudburst was the last thing the area needed. Preliminary Monday rainfall totals included 1.38 inches at Tinley Park and 1.29 at Frankfort—and the rain was still falling.

Temperatures have crashed overnight. Another pneumonia front has swept across the area and Chicagoans awaken to full fetch northeast winds in its wake.

Illinois, Indiana farmers rained out of their fields

It's planting season on Midwest farms. And while the process has proceeded expeditiously in Iowa, Nebraska and Minnesota, the U.S. Department of Agriculture says Illinois farmers have only been able to plant 4 percent of the state's corn. That compares to a five-year average of 43 percent. Only 2 percent of Indiana's corn is in the ground versus an average of 25 percent.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
What was the deadliest tornado ever to hit Illinois?
Pat Beranek, Downers Grove

Dear Pat,
Illinois' deadliest tornado and this nation's deadliest are one in the same; the Tri-State
Tornado of March 18, 1925. That storm took a record 695 lives with 613 of the deaths
occurring in Illinois, as it cut a continuous 219-mile-long path of F4-F5 destruction
from southeast Missouri to southwest Indiana. The town of Murphysboro, in Downstate
Illinois, suffered 234 of the fatalities, the most ever in a single community.

The storm began around 1 p.m. near Ellington in southeast Missouri and dissipated 3.5
hours later near Petersburg in southwest Indiana. The twister's average speed was 62
m.p.h. and at one point reached a record 73 m.p.h. between Gorham and Murphysboro
as it sped across southern Illinois.

It was a weekend of temperature chaos in the Chicago area. After Friday’s burst of
warmth sent readings well into the 80s across the region, the mercury plunged Saturday
afternoon as a “pneumonia front” dropped temperatures into the upper 30s and lower 40s across the city and north suburbs. This bizarre scenario resulted in wind chills along the North Shore and heat indexes in south suburban areas.
Cold front moving in
Warm weather returned to most of the region Sunday afternoon as gusty south winds
boosted readings back into the 70s and lower 80s, but it also set the stage for another round
of showers and thunderstorms expected to arrive Monday ahead of a cold front approaching
from the Plains. This front generated a rash of hail and high winds from the
southern Plains to the mid-Mississippi Valley Sunday afternoon, but at least 10 tornadoes
were reported, one as close as Dickeyville in southwest Wisconsin.
Several clusters of showers and thunderstorms are slated to move through the Chicago
area Monday. With the atmosphere brimming with moisture and frontal systems
enhancing the area’s sharp temperature differentials, heavy rainfall, hail and gusty winds will be possible.
--By Steve Kahn, WGN Weather Center Meteorologist

Dear Tom,
When can I safely put my young tomato plants out without a chance of frost
killing them?
Charles Heidgen, Batavia
Dear Charles,
Noting that you live in far west suburban Batavia, we would caution to not
put out your tomato plants without protecting them on chilly nights until at
least the middle of May. If you lived in the city -- especially near Lake
Michigan -- it would be a totally different story; it would probably be safe
to plant them now. With Lake Michigan water temperatures already in the
middle and upper 40s, a combination of the lake's warming influence and the
urban heat island effect make the threat of frost negligible there after
about April 15. Further inland it is a far different story, and frost can
form on clear, calm nights well into May. Typically, areas west of the Fox
River don't cross the 90 percent safe-to-plant threshold until about May 20.

After reveling in the first truly warm days of the year Friday and Saturday, a strong cold
front sent temperatures crashing across the area Saturday afternoon. At Highland Park
the mercury plunged 28 degrees from 70 to 42 in just 14 minutes shortly after 1 p.m.
and by 5 p.m. the temperature there hovered at 37 degrees while the Kankakee area still
basked in the lower 80s. The large temperature disparity generated waves of showers
and thunderstorms across the region that produced heavy downpours and hail.

Sunday morning will open rainy, damp and chilly, with brisk southeast winds holding
temperatures in the lower and middle 40s. But the early season warmth is expected to
surge back into the area Sunday afternoon with the mercury rapidly rebounding to the
lower 80s, as gusty southerly winds initiate the temperature comeback. Scattered
showers and thunderstorms will develop in the increasingly humid air mass, but a more
general thunderstorm outbreak is slated for Monday as an approaching cold front
threatens to trigger thunderstorm clusters capable of producing repeat heavy rain
episodes.

THE WEEK AHEAD

Skies skies are expected to partially clear by Tuesday, and the remainder of the week
should feature seasonable temperatures and generally dry conditions except for some
rain late Thursday into Friday.

Dear Tom,
We live near San Antonio and just heard a report of teacup-size hail. How big is that?
-Ann and Chuck Keeling

Dear Ann and Chuck,

Severe weather season always brings a rash of hail reports along with a load of descriptive
size adjectives. Most hail identifiers can be associated with a specific diameter, like pea
size (one-fourth of an inch) or golf-ball size (1 3⁄ 4 inches), giving an accurate mental
image of the hailstone. Other terms such as teacup, hen egg and grapefruit, items which
can vary in size, are less easily visualized. Most hail charts list teacup hail at about 3
inches in diameter. Other effective size-related terms in common use include penny (
three fourths of an inch), quarter (1 inch), baseball (2 3⁄ 4 inches), tennis ball (2 1⁄ 2 inches)
and softball (4 1⁄ 2 inches).

The 2009 Fermilab/WGN-TV Tornado and Severe Weather Seminar is to be held Saturday, April 25, at noon and repeated in its entirety at 6 p.m. We hope you can join us! The programs are free of charge, require no tickets and feature seating on a first come, first served basis. This is the 29th year we've presented our Fermilab tornado seminars, and we look forward to seeing you!

Map to Wilson Hall and Fermilab (provided by Fermilab)

Click here for full presentation descriptions for all the scheduled speakers

Click the link below for the scheduled list of speakers and topics; and look for more details about each presentation in the days ahead!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

More of Friday night's rainbow shots

Thanks to James Hillis for passing on these great shots of the spectacular rainbow that graced Chicago skies Friday evening after some showers passed through the area. These phots were taken on the University of Chicago campus near 55th and Woodlawn at about 7:15 p.m.

Photos by James Hillis

Steve Kahn WGN Weather Center

Temperatures surged to July levels Friday, topping out at 84 degrees at
O'Hare International Airport and 85 at Midway-but soaring as high as 88
degrees in northwest suburban Libertyville, 87 at Wheaton and 86 at
Gary.
More than six months has passed since an 80-degree temperature graced
the area. Only one year in five produces warmth at Friday's levels so
early in the season. Last year, it took another five weeks-June 2-for an
84-degree temperature reading here.
A dramatic but temporary break in Saturday's unseasonable warmth
threatens to ignite the Chicago area's first organized outbreak of
severe weather. The same powerful temperature-slashing cold front that
lopped more than 50 degrees off readings in Plains on Friday is to sweep
across Chicago with potentially thundery weather between 3 and 5 p.m.
Saturday. The windshift it produces is likely to send temperatures into
a dive off the day's low 80-degree highs-a decline which may reach 40
degrees by evening.
Thunderstorms bombard Midwest with ground-burying hail
A barrage of hail battered areas from southeast Nebraska to Upper Michigan
late Friday. Two-inch diameter hail fell in several communities near La Crosse, Wis.,
while hail two inches deep covered the ground near Rockland in western
Upper Michigan.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
The "change of seasons" is often cited as the explanation for severe weather
in the spring. So why is spring traditionally the tornado season and not the
fall?
Randall George
Dear Randall,
The explanation is not just the "change of seasons"; it's the kind of
change, and it has to do with the stability of the atmosphere.
Powerful currents of warm, rising air -- so-called "updrafts" -- provide the
energy that feeds thunderstorms. When the lowest few thousand feet of the
atmosphere is warm and it is much colder aloft, the warm air gives birth to
updrafts, and the atmosphere is said to be "unstable." That's thunderstorm
weather.
The atmosphere is thunderstorm-prone (unstable) in the spring because the
air aloft is still cold with the lingering chill of winter, but
strengthening spring sun is rapidly warming the surface layer. It's the
opposite (stable) in the fall. Air aloft still retains summer heat and the
surface layer is cooling.

--WGN-TV Weather Center

Photos courtesy of Monika Bec Thorpe, former WGN Weather Center intern

Temperatures on Friday jump to summer levels. It's a change guaranteed to capture Chicagoans' attention in a month that has averaged 2.5-degrees below normal to date. Wind trajectory forecasts, which allow the tracking of air movement, indicate Friday's warming originated 24 hours ago in Mississippi and Louisiana, where Thursday highs hit the mid-to-upper 80s. Powerful southwest winds--expected to reach 60 m.p.h. several thousand feet above the ground this afternoon--will transport that warmth into Chicago so swiftly that the usual level of cooling that occurs in northward moving air is likely to be overcome. This suggests Chicago’s official high Friday may well reach 85 degrees--a level 24 degrees above normal and more typical of July than April. It took another five weeks for similarly warm temperatures to occur a year ago.

Not only are temperatures to warm here, humidities surge in coming days as well contributing to a dramatically different, more spring-like feel to the air--but also possibly fueling thunderstorms as a cold front sags south toward the area late Saturday. That front could shift Saturday’s strong and unseasonably warm south/southwest winds to the east Saturday night into Sunday morning producing cooling before warm air resurges Sunday afternoon.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
I remember back in the 1950s when several fisherman perished in a seiche. Can you
provide some information on this?
Kathleen Madden, Chicago

Dear Kathleen,
It was back on June 26, 1954 when a killer 8-10 foot wall of water called a seiche
(pronounced saysh) swept eight unsuspecting fishermen off the Montrose Harbor pier
to their deaths. The seiche was caused by an outflow of cold air rushing out of a
fast-moving line of thunderstorms speeding southeast across southern Lake Michigan
in excess of 60 m.p.h. The cold outflow caused a rapid rise in air pressure that pushed
a slowly-building bulge of water toward the southeast shore of the lake. As a result,
water levels dropped on the Chicago shore and rose on the Michigan/Indiana side. The
surge then moved back to the Chicago shore as a large wave, taking nearly 90 minutes
to make the return trip.

Chicago's warmest weather to date in 2009—and the area's warmest weekend in more
than six months--is on the way. The warming cycle, likely to extend through the
weekend, began with Wednesday’s 61-degree high and builds Thursday with the
predicted 74-degree high. Southeast winds will slice ashore off Lake Michigan limiting
shoreline readings to the low and mid-60s. Lake cooling will be extinguished Friday
and Saturday by powerhouse south/southwest winds gusting at times to 40 m.p.h. and
being driven by falling pressures as a significant large-scale spring storm develops
over the nation's midsection this weekend and early next week.

Chicago's meteorological wild card this weekend revolves around the potential for
thunderstorms—principally Saturday evening and in areas north toward the Wisconsin
line. The outflow from these storms may provoke several additional thunderstorms as
far south as the Chicago area Saturday night and early Sunday. A more substantial rain
risk arrives with thunderstorm clusters later Sunday night and Monday. This period
could include the area’s first organized severe weather outbreak of 2009. A suite of
computer projections hints a corridor from Texas and Oklahoma northeastward into
northern Illinois and Wisconsin may be in for 1 to 4 inches of rain the next 5
days--heaviest just west of the Chicago area.

More than half of years have seen an 80-degree reading by now

April 20 has been the average date of Chicago's first 80 degree or higher temperature
the past 11 years--and weather records at Midway Airport reveal more than half of the
past 81 years there (since 1928) have hosted an 80 by this date.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Your column about rainbows sparked a lively argument with a friend.
He says rainbows are shaped like arches like the St. Louis Arch.
I say they are circular.
Susan Taylor

Dear Susan,

The arc of a rainbow is the same for all rainbows, and the arc is always circular. Triton
College astronomer Dan Joyce explains, "Most of the time, because we see only a
fraction of the full rainbow, it is tempting to perceive what we see as a parabola or
some other non-spherical conic section -- but it's a circle."

Because a rainbow always appears at an angle of 138 degrees from the sun, it is seen
on the opposite side of the sky from the sun. The best view of a rainbow's spectacular
color display is afforded not from the ground, however, but from high-flying aircraft.
Occupants of jet planes can sometimes see a rainbow's entire full circular sweep from
top to bottom.

Chilly air loosens its grip on the Chicago area Wednesday--the first stage of a dramatic multiday warm-up expected to carry area temperatures to the highest levels since early September. Tuesday's blustery 43 degree peak reading matches the normal high here on March 8. And while a chilly rain fell much of the day across Chicago, record snows walloped the upper Midwest--focusing on Michigan’s Upper Peninsula, where up to 21.2 inches of snow fell at Rockland near Houghton. Other Upper Peninsula totals included 19.1 inches at Sidnaw, 18 inches at Alberta and 10 inches at Twin Lakes.

By contrast, record-breaking heat headlined western and southern U.S. weather. The eastward expanding dome of unseasonably warm air, expected to bring Chicago the warmest weekend since early October, produced sizzling early-season highs of 107 degrees at Thermal, 101 at Riverside and 95 at Los Angeles--all in California--while Corpus Christi, Texas, topped out at 95.

Warm air holds more moisture than cool air and computer projections suggest the water content of the air over Chicago is to more than triple over the next five to six days. The atmosphere here is to hold an estimated 0.40 inches of evaporated water Wednesday--but by late Sunday, that amount is to surge to 1.40. Dew points, meteorologists’ preferred measure of atmospheric water content, are to surge to 60 degrees this weekend for the first time since Oct. 6. Increased dew points lend a warmer "feel" to the air.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
When you present "normal" spring temperatures, are these really the averages gathered
over all of the years of record, or are they obtained by taking some low point in winter
and a high point summer and plotting a rising line from one to the other?
Ralph Kravis, La Grange, Ill.

Dear Ralph,

Normals for a location are derived from temperatures observed there during a 30-year
period, currently the years from 1971 through 2000.

At a specific location, average high and low temperatures for a given day, say Aug. 10,
are obtained by averaging the 30 daily highs and 30 daily lows observed on Aug. 10 in
all years from 1971 through 2000. The same is done for all days of the year. The daily
averages, which bounce up and down a few degrees from one day to the next, are
"smoothed", and those smoothed values are adopted as the normal daily temperatures.

The late-season snowflakes, which threaten to flutter earthward in
above-freezing ground-level temperatures Tuesday, aren't as unusual in
Chicago as many here may think. The final flurries of the season came on
April 28 last year, and a review of Chicago's official snow records
dating back to 1885 reveals 66 of the past 124 seasons-53 percent of
them-have produced at least a trace of snow beyond April 21. Lengthening
days and strengthening spring sunlight have all but eliminated prospects
for anything resembling a significant snowfall here (6 inches or more).
But, the pool of unseasonably chilly air has settled south into the area
overnight and computer models have dropped subfreezing temperatures to
within 1,000 to 1,200 feet of the ground Tuesday. Snowflakes have been
known to fall through as much as 1,000 feet of above-freezing air
without completely melting-reasoning which backstops Tuesday morning's
prediction of snowflakes. With the ground warm, the threat of
accumulation is nil.

A huge late-week temperature surge, predicted to ride powerful south
winds into the area by Friday and Saturday, is to propel Friday's high
to 86 degrees-just a degree away from the record.

Gusty south to southwest winds-at times up to 40+ m.p.h. Friday-are
predicted to push late-week warmth right up to the lake, completely
overpowering lake winds that would otherwise cool the area-and setting
the state stage for the year's warmest weather to date.

Midway having its 2nd wettest year in 81 years

Wet weather has kept farmers from their fields to date this spring.
The 9.81 inches of precipitation on the books at Midway Airport since
March 1 is the site's second heaviest in 81 years of weather records.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Can the relative humidity ever be greater than 100 percent?
S. Wahrman

Dear S.,
Surprisingly, yes, and the condition is known as supersaturation. At any given
temperature and air pressure, a specific maximum amount of water vapor present in the
air will produce a relative humidity of 100 percent, and air in that state is said to be
saturated. Supersaturated air literally contains more water vapor than is needed to
cause saturation.

Airborne water vapor begins to condense onto impurities in the air (such as salt
particles and dust) as the relative humidity of moist air approaches 100 percent; a
cloud (or fog) forms. In absolutely clean air devoid of impurities that ordinarily serve as
condensation surfaces, the humidity can climb to incredible levels of supersaturation
-- 400 to 800 percent -- before condensation begins. Realistically, though, air is never
totally clean.

As low pressure makes its way northeast into lower Michigan on Monday,
clouds and rain stay over northeastern Illinois. The farther north the
low pressure area moves, the more cold Canadian air is drawn into the
system. Heavy snow is forecast for upper Michigan on Monday and Tuesday.
As the colder air is pulled south, there is an increased chance of rain
and wet snow in northeastern Illinois. Precipitation finally ends over
Chicago later Tuesday.

Heat west, severe storms south
Record or near-record heat occurred Sunday in California. The heat
should continue and even intensify Monday. Severe storm watches and
warnings were issued in Mississippi, Alabama, Georgia and Tennessee.

80s expected in Chicago
The midweek temperature turnaround peaks Friday as southerly flow and
sunny skies allow Chicagoland readings to climb into the 80s. The warmth
may continue through next weekend, but a cold front could sink south
through Chicago and create huge temperature disparities: Readings could
range from the 50s north of the front to the low 80s south of it.
--By Paul Dailey, WGN Weather Center Meteorologist

Dear Tom,
Do rainbows only come out in the summer (when it is warm)?
Sam Fortuna (age 5)
Dear Sam,
Rainbows can appear in the sky at any time of the year because temperatures
are not involved in their formation. Unfortunately, the sky conditions that
are necessary to produce rainbows rarely occur during the coldest part of
the year, and so we almost never see them in the period from November
through February.
A rainbow can form only when bright sunlight shines directly on water
droplets (like raindrops) and the observer is in the proper place to see it.
But in the winter, the usual situation when it is raining is a gray, gloomy
and solidly overcast sky with no direct sunlight. Breaks in the clouds that
let sunlight shine directly onto raindrops usually occur only with showery
rain such as thunderstorms, which are mainly warm-season weather events.

As a deep low pressure system moves out of the southern plains into the Ohio
Valley, a broad area of rain on the north side of the storm will spread into
the southern Great Lakes. Counter-clockwise flow around the low will steer
easterly winds off 40-degree Lake Michigan waters into northeastern Illinois
and southeastern Wisconsin. South of the storm center, and east of the
associated cold front, the area of severe storms will shift east, impacting
Tennessee, Mississippi, Alabama and Georgia today.

WEST COAST WARM-UP

As a high pressure ridge moves over the West Coast, an off-shore flow is
developing over southern California which will bring upper 90s and
100-degree readings to the valleys over the next few days. Los Angeles is
forecasting highs in the low to mid 90s through Tuesday.

WEATHER TRANSITIONS MIDWEEK IN CHICAGO

Later Wednesday, a southerly flow should return to Illinois. By Thursday,
the strengthening flow will pull significantly warmer air into
northeastern Illinois with readings reaching the lower to middle 70s.
Computer models indicate this flow will continue into next weekend with
Chicago in store for it's first 80s of 2009 on Friday and Saturday.

Dear Tom,
I can get pink skin from the sun, even in the winter. Does this not mean that my skin is
producing vitamin D?
Laurie Black

Dear Laurie,

With regard to exposure to sunlight during the winter, Dr. Bryan Schultz, an Oak Park
dermatologist, tells us, "With Chicago's winter sun at about 10 percent of summer's
intensity ... one is much less likely to get adequate vitamin D that way." Schultz explains
that other factors are also at work. “Skin may turn pink from cold or wind, but this does
not produce vitamin D." In addition, shorter winter days and winter cloudiness greatly
limit exposure to the sun, and winter clothing reduces the amount of skin area exposed.
However, Schultz cautions that prolonged exposure to winter sun "may still cause the skin
to turn pink from UV [rays], especially with reflection from snow which may double the
dose."

Chicago temperatures head back into the 70s Saturday afternoon for only
the third time this year -- and over a wider area than on Friday. The cool
easterly lake breezes predicted to develop in the afternoon are likely
to be the weakest in days, limiting the inland penetration of
lake-cooled air to within a mile or two of the shoreline. While readings
surge back to the mid-70s observed Friday at west suburban Oswego (76
degrees), Elgin (75), Geneva (75) and Darien (74), immediate lakeshore
area highs will hold to the low and mid-60s from Grant Park north to
Waukegan and Kenosha.

Highs on Friday reached 70 degrees at O'Hare and Midway Airports while
low 50s occurred from Hyde Park to the North Shore. The 74-degree high
predicted at O'Hare on Saturday would equal 2009's highest reading
recorded a month ago on St. Patrick's Day -- but changes loom. A cold
front passes Saturday night as an approaching storm draws cooler air
into its circulation. That storm is to lift from Texas into central
Illinois between midday Saturday and Sunday. Initially, light
post-frontal winds Sunday morning are to strengthen as air rushes into
the intensifying system. This should send Chicago-area temperatures
plummeting into the 40s as showers build into steadier rainfall by
Sunday afternoon.

Thundery, wind-driven Colorado snows reach 30-plus inches; Texas hit with
deluge!
Thunder-embedded snow whipped by 63 m.p.h. wind gusts at Denver
International Airport fell with such intensity across Colorado's
foothills and mountains Friday that 4.5 inches came down in a single
hour near Aspen -- as heavy as any ever observed here in Chicago. By late
evening, 34.5 inches had been measured at Pinecliffe, Colo., and to the
north, Cheyenne, Wyo., had 21 inches down.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Has it ever officially snowed in June in the Chicago area?
James A. Ulrich, Riverside
Dear James,
In the 138 Junes of Chicago weather records dating back to 1871, only once has this city recorded an official June snowfall, and that occurred on June 2, 1910. It was a very un-June-like day with a high temperature of only 55 degrees and a low of 43. Chicago weather historian Frank Wachowski said that during a thunderstorm rain, hail and wet snowflakes were observed. Rainfall that day totaled 0.41 inches, but the snowfall was just a trace. It's been a long time, but other traces of snow have fallen here in late May including May 25, 1924, and May 26, 1889. The city's latest measurable snowfall was 0.2 inches on May 11, 1966. Snow has fallen in Chicago in 10 months of the year; only July and August remain totally snow-free.

For those Chicagoans desperately in search of some meteorological
affirmation that spring would eventually produce a mild day, Thursday
was the gift that just kept on giving. Not only was it sunny (for the
first time in a month, there wasn't a single cloud in the sky) but
temperatures surged above 60 degrees at O'Hare and Midway Airports for
the first time in April. A number of western suburbs even recorded low
70s, among them Wheaton with 73 degrees, Oswego with 72 and Plainfield
with 71. So slow is the eastward progression of weather systems across
the U.S. that Friday and Saturday's predicted sunshine here-in marked
contrast to the late season snowstorm lambasting the Rockies, including
the Denver area-is to continue heating the air mass in place. That lays
the groundwork for the back-to-back 70-degree highs predicted both days
in all but lakeside areas. The light easterly lake breezes that
occur-weaker and less able to deliver their chill as far inland as in
recent days-should yield shoreline temperatures that lag those farther
inland. Not since St. Patrick's Day has the city been treated to a 70
degree or higher official temperature. That's unusual. Weather history
indicates 80 percent of years here since 1928 have seen more than the
single 70-degree high on the books so far this season.

The 74-degree high predicted Saturday would be the area's
first weekend 70-degree reading in six months.

A blustery temperature downturn hits with a cold frontal passage late
Saturday night, and rain follows Sunday and Monday. But signs of even
stronger warming grow and a suite of computer models suggest an
atmospheric setup capable of delivering 80-degree warmth late next week.

Dear Tom,
What is a "landspout"?
Dennis Gilliland

Dear Dennis,

It's a colloquial term for a tornado, usually rather weak as tornadoes go, produced by a
thunderstorm that is still in its initial stages of intensification (during which time it
rarely produces severe weather). Landspouts are so-named because, in appearance,
they resemble weak Florida Keys waterspouts over land.

Most tornadoes are produced by a special breed of thunderstorms known as "supercell
thunderstorms" -- enormous, severe, rotating (in the sense that air in the 10-50 mile
wind field in which supercells are embedded spirals inward) and, most uniquely, they
persist for hours. Most thunderstorms move through a life cycle of an hour or less,
then die away. Landspouts are the products of non-rotating thunderstorms that, in
other respects, are not severe.

Wednesday's temperatures soared to their highest levels in a week.
Readings across many western suburbs topped the city's official high of
57 degrees at O'Hare International Airport. Among the warmer readings:
62 at Elgin, 61 at Algonquin, West Chicago and Buffalo Grove and 60 at
Aurora. Rockford's 65-degree high qualified as northern Illinois' warm
spot on Wednesday while Lake Geneva, Wis., hit 63.

Easterly breezes continue off Lake Michigan an eighth and ninth day
Thursday and Friday, but at slowly declining velocities. That should
decrease the portion of the metropolitan area these winds are able to
cool. While readings hover in the 50s near Lake Michigan on Thursday,
inland highs will reach the 60s-and may well increase to the low 70s on
Friday. The best news of all is that a slowdown in the approach of a
windy, wet Saturday night/Sunday storm has allowed 70-degree highs to be
extended into Saturday, especially away from the shoreline. A weekend 70
hasn't occurred here since October.

Chicago's only 70-degree high of 2009 occurred nearly a month ago on
St. Patrick's Day. Weather records suggest that makes this area overdue
for another 70. Over the past 81 years, an average of four 70s have
typically been on the books by April 16 at Midway Airport, and 80
percent of the years there since 1928 have already recorded two or more
70s by this date.

Late-season snow may hit Denver after a 74-degree day

Denver hit temps in the 70s Wednesday-but the area may be blanketed by snow
Friday into Saturday-perhaps 10 to 20 inches in the foothills.

Dear Tom,
What are the longest and shortest intervals between Chicago's first flakes in the
autumn and the last ones in spring?
Matt Mills

Dear Matt,
The period you describe is sometimes referred to as the snowing season and in Chicago
it typically extends for 174 days from Oct. 30 to April 21. The city's shortest snowing
season on record spanned only 109 days from Nov. 21, 1945 to March 9, 1946.

Chicago's longest snow season, recorded in the winter of 1909-10, covered 235 days
from Oct. 11 to June 2, a date that marks the city's latest-in the-season snowfall.

The last snowflakes recorded in Chicago this season fell April 6, and if no more snow
falls the rest of this spring, the 2008-09 snow season will enter the books at a lower-
than-average 163 days from Oct. 26-April 6.

Our friend and pilot Anson Mount sends us these photos, taken as he headed this
morning to downstate Alton, Illinois. These shots were taken between cloud layers
while at 6,000 ft. over Chicago Heights. It’s been fascinating to watch these clouds
evaporate on satellite loops with the arrival of dry air. Temperatures have taken off as
skies have cleared—reaching the 60s in our western suburbs. It’s a sign the strong
mid-April sun is ready to go to work anytime we can get the sun to shine!! Thanks for
the great shots, Anson!!

Tom Skilling

Photos courtesy of Anson Mount, Algonquin, Illinois

It's not easy this time of year keeping temperatures as chilly as Tuesday's March-level
44-degree high--a reading 14 degrees below normal. The factors critical to making that
happen were all in place--a solid overcast, sporadic light rain and a northeast wind off
Lake Michigan. The reading marked Chicago's chilliest April 14 high in nearly three
decades--since the 35-degree peak reading on the date in 1980. The appearance of
sunshine late Tuesday in Rockford and Janesville and Madison, Wis., warmed readings in
those cities to 54, 57 and 59 respectively--levels significantly higher than the stinging
37- and 38-degree highs at Wilmette and Glencoe. The increasing amount of energy
delivered by sunlight will in the months to come ultimately defeat any move on the area
by the reservoir of cold air over what's left of Canada's steadily melting snowpack.
Chicagoans have watched the hours of daylight here lengthen from 9.1 hours in December
to Wednesday's 13.4 hours--an increase of more than 4 hours. At the same time, the
sun's daily track across the sky places it more than 30 degrees higher at midday than four
months ago as winter was getting underway. This sends sunlight three times as energetic
as in December cascading down on Chicago--a development which boosts temperatures.

Strong storms sweep drought-stricken Florida

Potent thunderstorms, at times more than 10 miles tall, brought much needed 1-inch+
rains to the Sunshine State on Tuesday, but the storms also generated a tornado
touchdown near Holiday, Fla. The twister—of EF1 intensity (95+ m.p.h.)— damaged at
least 50 homes.

-Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom:

So far this season we have had 56 days where the temperature did not reach 32
degrees. How does that compare with an "average" winter season?
Bob Matthei, Lake Bluff, Ill.

Dear Bob,

Chicago normally experiences 41 days per winter season on which the temperature fails
to climb to 32 degrees. That's the result of a computer sweep of the city's entire
temperature data base, 1871 to the present. (And by "winter season" we are referring to
the period from October through April, rather than the precise but more limited
definition of meteorological winter, December through February.)

We've logged 56 sub-32 degree days this winter, or 36 percent more than average -- a
statistic that will come as no surprise to winter-weary Chicagoans awaiting genuine
spring warmth. Only 22 winters out of 138 have produced more sub-32 days.

Chicagoans brace for early March level temperatures Tuesday, with readings more than
15 degrees below normal, as the area moves into an 11th consecutive day of subnormal
temperatures. This month's 41.0-degree average temperature is 3.6-degrees below the
long-term 138-year average--cool enough to rank among the chilliest 20 percent of
April 1-14 periods on the books. It's the first April here in 25 years that has failed to
host a single 60-degree daytime high.

The Chicago area remains mired in the same damp, raw northeasterly flow responsible
Monday for the chilliest Cubs home opener since 2004. The storm system behind the
gray skies, expected to linger into Wednesday morning, has become ensnared in what
meteorologists refer to as an atmospheric blocking pattern. These patterns involve jet
stream configurations that impede the forward movement of weather systems under
their control. In this case, a pool of warm air aloft over southern Canada has
encouraged jet stream winds to split into two distinct channels. As these streams
re-converge over the Northeast U.S., the confluent winds produce a pressure build-up
aloft that forces air to sink to the surface on a massive scale. A high pressure system
results which slows weather system movement to the west.

City's wettest meteorological spring in 26 years

The 8.61 inches precipitation tally since March 1 at Midway Airport is not only twice
the long-term 81-year average, it makes this the wettest spring to date since 1983
and second wettest of the past eight+ decades at the South Side site.

-Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Please settle this dispute between me and my brother. Has Chicago ever had a July day
with a high below 60 degrees?
Patrick O'Heath

Dear Patrick,

Chicago has experienced some chilly days in July but never one with a high less than
60. The chilliest July maximum on record here is 60 degrees observed on July 8, 1883.
In those days the city's official temperature site was downtown near Madison and
LaSalle Streets and the brisk north-northeast winds off Lake Michigan that prevailed in
the wake of a cold front's passage contributed to the day's anemic high. There have
been sub-60 highs at the end of June, most notably the three-day string in 1902 of 58
degrees June 28 and a pair of 59s on the 29th and 30th. The only August day with a
high below 60 was Aug. 30, 1915 with a maximum temperature of 58.

Brisk east winds held spring warmth in Chicago at bay once again Sunday,
keeping most area temperatures in the 40s near the lake and 50s inland. It
has been nearly three weeks since the city's last 60-degree day on March 24
and almost a month since this spring's singleton 70 was recorded on St.
Patrick's Day when the mercury soared to a balmy 74 degrees.
Monday will be anything but springlike here with temperatures hovering in
the lower and mid 40s as the area is soaked by a wind-driven rain. Sunshine
should return my midweek, but the persistent lake winds will continue to
chill the area with the city continuing to struggle to reach the elusive
60-degree mark. More rain is expected by next weekend, but southerly winds
ahead of the approaching storm system could finally boost the mercury well
into the 60s Friday.

Easter sunshine fades in the afternoon
Despite Sunday's coolness, the area was bathed in total sunshine much of the
day. It was looking like the city would record its first Easter with 100
percent of possible sunshine since 1977, but advancing clouds ahead of
Monday's rainstorm arrived by mid-afternoon, capping the day's sunshine at
just 76 percent.
--By Steve Kahn, WGN Weather Center Meteorologist

Dear Tom,
With the Cubs home opener today, I wonder: What kind of weather has the team
encountered over the years?
Derrick Jabczynski
Dear Derrick,
Chicago Cubs home openers are typically cold-weather affairs, a combination
of the early April date and Wrigley Field's proximity to chilly Lake
Michigan. Today's opener will be no exception with game-time temperatures
expected in the lower 40s combined with stiff east winds and a cold rain. A check
of Cubs home openers dating back to 1954 shows that 56 percent of the
games have been played with temperatures in the 30s or 40s. The team's
coldest opener took place on April 8, 2003, with the mercury at an icy 32
degrees. There have been some warm exceptions. On April 22, 1960, against
the San Francisco Giants, the first-pitch temperature was a summery 80
degrees with a stiff 25 m.p.h. south wind blowing out to left field.

Chicago's spring has been a cool one to date, but the upcoming week shows some signs of milder weather--especially for areas away from the lake. The city has not recorded a temperature of 60 degrees since it reached a balmy 69 degrees on March 24, and so far, this year has logged only one day in the 70s: a delightful 74-degree high on St. Patrick's Day. With plenty of sunshine expected on Easter, the city’s official thermometer at O’Hare International Airport could possibly reach the 60-degree mark, though areas near the lake will struggle to get out of the 40s as chilly east winds blow. Monday promises a different story as a storm system spins into the Midwest, dropping readings back into the 40s and setting up a steady rain that could delay or postpone the Cubs home opener. This could be the second year in a row that rain will impact Opening Day. The start of last year's Cubs home opener was delayed by a chilly rain, but once skies cleared, readings rose to around 60 degrees as a warm front passed. Milder conditions with more inland 60s are slated to return Wednesday and linger through Friday, but lake winds will continue to chill shore areas.

NOTE: In the bar graph of Chicago's daily high and low temperatures of April 1938, the black bars represent the normal days.
Steve Kahn WGN-TV/Chicago Tribune Meteorologist

Dear Tom,
Last week you reported that when Chicago recorded the same high (50 degrees) three
days in a row (April 2-4), it was only the 193rd such occurrence. Has Chicago ever had
the same high four days in a row?
-Chris Goebel, Aurora

Dear Chris,

Since Nov. 1, 1870, the city has recorded the same high temperature on four
consecutive days 17 times—-a frequency of once about every eight years. The last time
this happened was Feb. 21-24, 2005, with a string of four 36-degree days; before that
four highs of 37 degrees were recorded Dec. 20-23, 1997.

Only once has the city achieved the same high five days in a row, and that was March
15-19, 1877, when the maximum temperature got stuck on the 30-degree mark. It may
happen again someday, but for now the city’s string of consecutive identical maximum
temperatures ends at five.

The 2009 U.S. tornado season -- noteworthy, until recent days, for a
twister count nearly 40 percent lower than a year ago -- erupted with
deadly consequences Friday. Powerful thunderstorms, which first exploded
late Thursday in the Plains, churned east Friday, spawning dozens of
tornadoes across six states from Tennessee and Alabama into the
Carolinas. One twister killed a woman and her 9-week-old infant in
central Tennessee while violent thunderstorms ripped roofs off buildings
and destroyed dozens of homes in Murfreesboro, 30 miles southeast of
Nashville. The 35 reports of twisters late Friday made it the most
active day of the 2009 severe weather season. It marked the sixth time
this year that 20 or more tornadoes dipped from U.S. skies in a single
calendar day. Ten such days had occurred by this time last year,
including three days with more than 50 touchdowns. Most active among
them was Feb. 5 when 131 twisters swept the U.S. The outbreak was
especially ill-timed because it coincided with Super Tuesday primaries
in 24 states.
Chill confirms 'lake wind' season
Chicago is in the midst of its "lake breeze season," widely recognized
to run from March into the first weeks of June. An easterly wind blows
of Lake Michigan's chilly waters 42 percent of the time in April --
second only to May, which sees an east wind 45 percent of the time.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
When was the city's coldest April? Has April ever been colder than March?
Anna P., Wilmette
Dear Anna,
At a time of year when Chicago's average temperatures are undergoing their
fastest increase, it would be rare to have an April colder than March, and
the city's temperature archives bear that out. Dating back to 1871 there has
been only one such occurrence, and that was more than a century ago in 1907.
In that year March, buoyed by nine days of 60 degrees or higher including
five 70s and even one 80, averaged 42.6 degrees; while April, chilled by 10
days in the 30s only two 60s and just one 70, averaged only 39.8 degrees --
making it the second coldest April in history. The city's coldest April
logged way back in 1884 averaged a chilly 38.8 degrees, but that year March
logged 36.4 degrees.

Strong northeast winds rushing into the latest spring storm to churn across southern
Midwest will take a big bite out of the mild 50 and low 60-degree temperatures
observed across the Chicago area Thursday. The 58-degree high at O'Hare International
Airport was April, 2009's warmest yet-but areas spared a cooling easterly afternoon
lake breeze posted even warmer readings. Highs included 64 degrees at Libertyville, 63
at Oswego and 62 at Buffalo Grove, Itasca and Geneva.

Downstate Illinois and Indiana are in for a soaking Friday. Rainfalls exceeding 1 inch
are predicted from St. Louis east to Bloomington, Ind., and Louisville, and severe
thunderstorms could erupt north to the Ohio River. Monster thunderstorms exploded to
life Thursday afternoon, towering 46,000 feet into the atmosphere.

La Nina fading, but summer impact here is not clear

The chilly La Nina which may well have played a role in winter's active Midwest weather
pattern is fading. Climate forecasters suggest the coming summer (June through
August) is to be one of 32 since 1950 between a La Nina and El Nino in the equatorial
Pacific. It's a development offers few clues on summer temperatures.

Dear Tom,
The level of Lake Michigan is up 13 inches from last year. That's great, but could you
express that in gallons of water?
Dan Fridley

Dear Dan,

The quantity of water that circulates through the Lake Michigan hydrologic system is
truly staggering. And expressing that volume in units as miniscule as gallons yields
numbers that are so huge as to be practically incomprehensible, but here it goes.
A 13-inch increase in the level of Lake Michigan's 22,300 square miles amounts to
5.044 trillion gallons of additional water (5,044,000,000,000 gallons). And that's not
all. Lake Michigan and Lake Huron are essentially one lake; their water levels rise and
fall in tandem. Thirteen inches of water added to the level of Lake Michigan means 13
inches added to the 23,000 square miles of Lake Huron as well, and that amounts to an
additional 5.202 trillion gallons (5,202,000,000,000 gallons).

Temperatures on Wednesday, benefiting from an abundance of sun and a
gusty west wind, made a run at 60 degrees at Libertyville, the Chicago
area's "warm-spot," where the high reached 58 degrees. But at the city's
official observation site, O'Hare International Airport, the 55-degree
high, though the mildest to date this month, was 5 degrees short. Nine
60-degree days are on the books in Chicago in 2009, yet not one has
occurred this month-and that's unusual. Since observations began in 1928
at Midway Airport, 67 of the past 81 years-83 percent of them-have
produced at least one 60-degree or higher April temperature by now.
It's not out of the realm of possibility that an easterly lake breeze,
expected to develop Thursday afternoon, might converge with the lighter
winds expected to dominate inland areas a good part of the day.
Converging winds, even with the comparatively low velocities predicted
Thursday, may be just enough to boost temperatures a few degrees through
"compressional warming" and send a few sections of the Chicago area into
the low 60s.
But jackets and sweaters are the order for the day along Lake Michigan
where an initial temperature romp into the 50s could be followed by a
pullback to the 40s as lake breezes get going.

Dear Tom,
What is meant by the term "carbon sequestration"?
Dorothy Manning

Dear Dorothy,

Carbon sequestration originally referred to the removal of carbon (in the form of carbon
dioxide gas, CO2) from the atmosphere by natural processes, mainly the absorption of
CO2 by the world's oceans and by photosynthesis in plants.

The tiny shells of ocean-dwelling animals contain carbon (chemically captured from
CO2 dissolved in ocean water). When they die, their shells and their store of carbon
sink to the ocean floor. Green plants use atmospheric CO2 during photosynthesis and
chemically store the carbon in their tissues.

The definition of carbon sequestration has expanded in recent years to include the
capture and storage or disposal of CO2 or other carbon compounds produced by
industrial processes in order to prevent their release into the atmosphere.

It's been 16 days since Chicago's temperature exceeded 60 degrees.
While many area residents are likely to be surprised to learn that nine
60s are already on the books in 2009, not one of those 60 degree or
warmer readings has occurred so far in April. In fact, the month's
highest temperature to date has been 53 on April 1.
This month's lack of 60s is in stark contrast with last April, which had
already generated a 64-degree high by this date.

Peak Chicago-area temperatures the next two days warm enough to produce
new April highs. While unlikely to reach levels that could be
characterized as warm, Wednesday afternoon's 56-degree high and the 58
predicted Thursday at least qualify as mild and are closer to seasonal
norms than any readings here over the past week. West winds overcome
lake cooling Wednesday and may allow some low or mid-60-degree readings
in the area's mildest locations.

A lighter wind regime predicted Thursday is likely to allow the shallow
layer of cool dense air that hugs the chilly lake surface this time of
year to cross onto the shoreline as an easterly lake breeze. This could
produce shoreline temperatures that reach 55 to 60 degrees then
backtrack to the low 50s.

Despite the recent chill, spring is running 2.2 degrees above normal

The chilly days of the past few weeks aside, meteorological spring 2009, which began
March 1, is averaging 2.2 degrees above normal.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Everyone's been talking about the White Sox opening games being snowed out in 1982.
But I remember the "second" opener on April 16 was also postponed. Can you confirm
this?
Eric

Dear Eric,
You are correct. After the first three attempts to open the home season were thwarted
by snow and cold, the Sox hoped to finally play baseball in Chicago on April 16. This
time it was heavy rain, not snow and cold, that caused the game to be canceled. There
was slight hope for baseball that night when the sun briefly broke through the clouds
around 5 p.m., but then the heavens opened and torrents of rain soaked the field. The
White Sox huddled helplessly in the clubhouse for more than two hours before the
game was finally called. The Sox finally began their 1982 home season the following
day by sweeping the Baltimore Orioles in a double header.

Richard Koeneman sent us this picture from his deck in Asheville, N.C. He tell us:

1/2 inches and counting!!! Temp is 29-degrees-- It was 74-degrees two days ago.

Thanks Richard!

It isn't easy keeping daytime temperatures as cool as they have been in
recent days. Monday's 40-degree peak reading was a whopping 24 degrees
colder than the 64-degree high on the same date a year ago and 14
degrees below the April 6 norm. It's just the latest afternoon
temperature this month to underwhelm area residents. The warmest
temperature that the opening week of April has managed has been 53
degrees. Only eight April 1-7 periods since 1928 at Midway Airport have
produced such limited daytime warmth. The chill is especially impressive
because the sunshine that bathes Chicago this time of year is three
times stronger than the sunlight of December.
Snow that fell heaviest across Chicago's west and south suburbs melted
quickly Monday as sunshine emerged from behind the clouds. But
lake-effect clouds were reassembling late Monday and were expected to
produce snow showers predicted to swipe Illinois' Lake Michigan
shoreline but directly hit sections of the Indiana and Michigan
snowbelt. A slow eastward shift of these clouds is predicted to take
the snow out of northwest Indiana as Tuesday proceeds.

Persistent chill could break -- at least temporarily -- next week
Three wet-weather systems may impact Chicago into early next week, with
the next one due to arrive with gusty winds Friday. But a number of cold
weather indexes may be the first signs of warmer temperatures in the
longer range.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
I remember a tornado that swept through Bourbonnais when I was a small boy
around 1960. Do you have any details on that storm?
Tim Guimond, Evanston
Dear Tim,
The tornado that you remember was an F4 storm that killed one and injured 70
on April 17, 1963, as it carved out a nearly 70-mile long damage path from
near Essex in Kankakee County to Medaryville, Ind., northeast of Rensselaer.
Some of the damage in Illinois was rated close to F5 strength as several
homes literally vanished. In Bourbonnais, the twister smashed the five-story
stone administration building at Olivet Nazarene University, damaged the
village hall, tore up a trailer park and partially unroofed the Maternity
Church. Earlier, the same storm complex brought hail and high winds to the
Chicago area with golf-ball-sized hail reported in Hinsdale and wind gusts
to 55 m.p.h. at Aurora.

Chicago area residents -- especially those in the south suburbs -- woke up to a wintry scene more typical of February than April. Fortunately, April's stronger sunlight eventually cleared the snow away. Thanks to everyone who sent us photos!
--WGN-TV Weather Center

Oak Forest

Photo courtesy of Julie Wimmer

Lemont

Photos courtesy of Dan and Doris Wagner

After a day that brought a variety of weather across the Chicago area,
including hail-producing thunderstorms and rain and sleet, the
precipitation potpourri shifted to a heavy, wet snow across the region
by Sunday evening. With temperatures hovering in the low 30s, colder
west and north suburban areas quickly acquired a snow cover, though some
melting was still occurring in the city and south suburban areas, where
temperatures were a bit higher.
With the snow expected to persist much of Sunday night, several inches
of accumulation were expected. However, totals could vary dramatically
because of melting and the potential for heavier bursts of thundersnow,
which appeared to be targeting the south suburbs and northwest Indiana.
This system brought heavy snow to portions of Iowa, where the town of
Conrad, southwest of Waterloo, received 10 inches of snow after
thunderstorms swept the area.
The snow should diminish to flurries Monday except for some heavier
lake-effect snow that is expected to gradually shift east into northern
Indiana. February-level highs in the middle and upper 30s will be the
rule, and strong, gusty winds will keep windchills in the low 20s much
of the day.
--By Steve Kahn, WGN Weather Center Meteorologist

Dear Tom,
It rarely snows in May but almost always snows in April. Are there more
Aprils without snow or Mays with snow?
Bill White
Dear Bill,
You raised an intriguing question that we immediately put Chicago weather
historian Frank Wachowski to work on. Wachowski found only 12 snowless
Aprils since 1885, the most recent occurring in 2004. Over the same time
period Wachowski noted 31 Mays with at least a trace of snow on the books,
the last May snow event occurring four years ago on May 2, 2005. The vast
majority of the 31 Mays with snow were just brief, one-day trace events --
but there were a few significant snowfalls. In 1903 the city recorded 1.3
inches on May 2, and 2.2 inches of snow fell on May 1-2 in 1940, a storm
that brought as much as 5 inches of snow to northwest suburban areas from
Elgin to Marengo, and up to 1 inch to areas as far south as Joliet.

It's hard to believe that Chicago's persistent cold, wet spring could take a turn for the
worse, but that is exactly what is expected to take place today. Chicagoans will be
greeted by a cold rain this morning, but farther north and west, conditions become
increasingly wintry. On Saturday night, blizzard conditions existed over Nebraska,
western Iowa and southern Minnesota, with up to 9 inches of snow forecast for portions
of eastern Iowa and southwest Wisconsin. Lesser amounts of snow were spreading east
across northwest Illinois and southeastern Wisconsin.

Chicago's changeover from rain/sleet to snow should be delayed until Sunday evening
because of strong northeast winds off the 40-degree Lake Michigan waters. As the
storm center moves east through Illinois into Indiana, cold Canadian air will flow into
northern Illinois on the storm's backside, forcing a complete changeover from rain to
wet snow. By Monday morning, accumulations could range from 6 inches north along
the Illinois-Wisconsin border to a couple of inches in Chicago's southern suburbs.
Depending on temperatures, snowfall totals could vary widely as storm total liquid
precipitation could run up to an inch, especially in areas where thunder occurs.

Dear Tom,
I recall a troublesome snowstorm in Chicago on April 2, 1975, but my husband is
positive it was at the end of March. I remember the date because it followed April Fool’s
Day. What do your records show?
-Mrs. L. Mazur

Dear Mrs. Mazur,
Chicago weather historian Frank Wachowski cracked open the record books, and he
confirms that your memory is correct. However, Wachowski commented
that "troublesome" is hardly a suitable description for the snowstorm that lashed the area
April 2, 1975. The storm put down 9.8 inches of heavy, wet snow that was mixed at
times with freezing rain and sleetand accompanied by howling northeast winds gusting
at 40 m.p.h. With temperatures mostly in the lower 30s, the snow stuck to everything
and power outages were widespread. It was officially the city's second-heaviest April
snowstorm.

A major early April storm gathers strength Saturday as it moves out of
Colorado into Kansas and heads for northern Missouri. Blizzard
conditions are forecast to develop over northeast Colorado and Nebraska
on Saturday and move into southeastern South Dakota, northwest Iowa and
southern Minnesota, with a foot or more of snow expected in those areas
Sunday. A winter storm watch is in effect for southwestern Wisconsin
Saturday night and Sunday. An extensive band of rain will spread east
and north of the low's center.

Chicago in for rain, then snow
The eastern edge of the rain shield should reach Chicago late Saturday
with rain continuing Sunday as the low moves through Illinois. An inch
or more of rain is possible, which could force swollen Illinois Rivers
out of their banks. Once the storm center reaches eastern Indiana,
strong northerly winds will pull colder air into northeast Illinois, and
rain will change to heavy wet snow Sunday night. The Chicago area could
experience significant accumulations as the snow is expected to continue
through Monday. Heavier lake-enhanced snow could move from the city's
West Side to the south as winds shift from the northeast to the north
and northwest.
--By Paul Dailey, WGN Weather Center Meteorologist

Dear Tom,
Okay, so we have had 50 inches of snow this winter, but now it's April. Dare
I hope the snow is now just a memory?
Jerry Donohue
Dear Jerry,
The likelihood of snow grows slimmer with each passing day, but Chicago's
snowfall records suggest it's a bit too soon to dismiss the possibility of
snow. On average (1885-2008), Chicago's normal snow season (October through
April) delivers 36.8 inches, and 98 percent of it has come down by April 4.
That means two percent, or 0.7 inches, is yet to occur.
April has produced measurable snow (at least 0.1 inch) in 66 years out of
124, or 53 percent of the Aprils. One-tenth inch of snow isn't very much, so
we'll arbitrarily define a "significant snow" as 3 inches or more. In April,
the chance of a storm with at least that much snow is one in four, and it's
one in 20 for a storm of 6 inches or more.

The year is off to quite a start. Even before the overnight rains, Chicago's precipitation
tally was closing in on 9.75 inches--an amount well ahead of the most recent 30-year
average of 6.25 inches. It is the sixth-wettest open tot a year in 138 years. It's little
wonder Lake Michigan's water level is running 13 inches ahead of the same time a year
ago.

With the growing season fast approaching, farmers will be closely monitoring
precipitation trends. Since March 1, Chicago's precipitation has fallen at nearly twice the
typical rate, totaling 5.2 inches. The period averages 2.87 inches.
South suburban areas basked in mild spring weather Thursday before winds shifted
northerly and a chill that gripped much of the area sent temperatures crashing.
By comparison, northeast winds limited readings up and down the Illinois and
Wisconsin shorelines to the 30s and 40s.

Severe weather breaks out as another storm looms

Thunderstorms towering more than 40,000 feet unleashed golf-ball-size hailstones
Downstate. At least 10 twisters dipped skies across Mississippi, Alabama, Louisiana
and Tennessee.

Dear Tom,
Is it true that girls have less chance of getting struck by lightning than boys?
Melanie Timms (6th grade), St.Rita School, Rockford, IL

Dear Melanie,
Yes, it is true. Ronald Holle and Raul E. Lopez of the National Severe Storms Laboratory
and E. Brian Curran of the National Weather Service conducted a comprehensive study
of lightning deaths and injuries in the United States and they found that boys and men
are struck by lightning about fours times as often as girls and women. Their statistics
indicated that males account for 84 percent of lightning fatalities and 82 percent of
lightning injuries.

It's not because lightning prefers to strike males. Rather, a much greater proportion of
men have outdoor jobs that put them in jeopardy (construction workers, farmers,
linemen, emergency responders). The study also found that men engage in
miscellaneous outdoor activities more often than women.

Our friend---weather enthusiast and, as it turns out, mountain-climber Mark Vogan,
sends us these amazing photos taken today (Thursday) in the mountains of Scotland.
Mark tells us:

"I was up the 16th and 18th highest of the so called "Munros" which are mountains in
Scotland at or above 3,000ft. Both these peaks are also 16 and 17th highest in all the of
UK..

A tough but satisfying climb which offers stunning views over much of the Central
Highlands of Scotland when clear, skies today were clear at the surface but hazy at
higher levels. Cool and breezy at the top with some snow drifts in sheltered areas away
from late winter sunlight, although the early April sun is taking a toll on dwindling
drifts up above the 3,000 ft level. In saying this, some drifts are likely 5-10 ft deep in
places where high winds often roar."

THANKS Mark!! Our thanks to Mark for giving us a look at the stunning Scottish
landscape! It’s an amazing place!

Tom Skilling

Photos courtesy of Mark Vogan, Glasgow, Scotland

Warm spring weather continues to be a no-show as April's opening week
promises to bring a continuation of the cold and wet conditions that
dominated March's final days. Chicago has not recorded a 60-degree high
since March 24, when the mercury peaked at 69, and prospects of another
60 remain dim for the foreseeable future.

Rain is expected to return by late Thursday as another storm system
approaches from the Plains.

More than an inch of rain could fall here by Friday morning, and wet
snow could mix in-especially west and north of the city-as strong north
winds gusting to more than 40 m.p.h. send temperatures crashing.

Sunday night storm a wintry threat

A second storm scheduled to hit late Sunday has a reservoir of cold air
on its northern flank and places Chicago perilously close to the
rain-snow line. Forecast trends have precipitation beginning as rain but
changing to wet snow by Sunday night as colder air enters into the
storm. Monday's Sox home opener should be a frigid affair, with snow
showers possible.

--By Steve Kahn, WGN Weather Center Meteorologist

Dear Tom,
Has Lake Michigan ever frozen over enough to enable travel from Michigan to Illinois?
Jack Brooks Orlando, Florida

Dear Jack,
Though constant wind and wave action combined with the vast reservoir of heat
contained in the lake prevents it from freezing completely, it has reached between
90-95 percent ice-coverage in this area's coldest winters including 1903-04, 1976-77
and 1978-79.

However, in very cold winters ice will form and bank up solidly along shore areas,
making it possible to travel that entire route over ice. An article sent to the Chicago
Tribune by Delicia Jane Lane in 1959 documents the severe cold that gripped the
Midwest in early 1899. "Lake Michigan froze as solidly as Lake Baikal. Horse drawn
cutters made trips to Michigan over the ice which remained firm until Feb. 22."