EXPLAINER: July 2008 Archives

Menacing thunderstorms rolled into Chicago on Thursday afternoon, blasting the area
with winds up to 70 m.p.h., hail and blinding, flooding rains. Winds reached 70 m.p.h.
at Gary, 62 m.p.h. at West Dundee and 60 m.p.h. at Addison, downing trees and power
lines as the towering 46,000-foot thunderheads swept through. Before striking
Chicago, the storms, which developed Wednesday evening in far southeast
Saskatchewan, produced a corridor of damage across the Dakotas, Minnesota and
northeast Iowa, with unconfirmed reports of winds as high as 115 m.p.h. Before the
storms struck Chicago, Midway recorded its seventh 90-degree reading of the year,
while O'Hare topped out at a steamy 89.

AUGUST, CHICAGO'S WETTEST MONTH, GETS UNDER WAY

August begins Friday and is currently Chicago's wettest month, with a normal rainfall of
4.62 inches. The last month of meteorological summer, August starts the slow
seasonal decline toward autumn. Average high temperatures drop from 83 on the 1st to
78 by the end of the month, and we also lose 1 hour and 14 minutes of daylight.

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

While much of the Chicago area dodged Wednesday's south suburban t-storms, rains
came down hard in a narrow corridor extending from Kendall and Grundy Counties east
into northern Indiana. Cottony cumulus clouds bubbled aloft to heights of 42,000 feet
and Doppler radar rain estimates ranged up to 2 inches. Rainfall gauges measured 0.44
inches at New Lenox and 0.20 inches at Frankfort. The downpours responsible were
accompanied there by frequent lightning.

The summer rains hit in a July about to close with more sunshine than any of the last
eight months. It's the first month with above-normal sun since November. Chicago
weather observer Frank Wachowski reports 77 percent of the month's possible sun -- a
total of 20,653 minutes out of a possible 26,775 is now on the books.

Wednesday's 90-degree high was the site's sixth reading to hit 90 degrees this year.
Thermometers at Alsip hit 93 degrees, 91 degrees at Palatine and 93 degrees at
Janesville, Wis.

MISSOURI SOAKED BY HURRICANE DOLLY'S REMNANTS WEDNESDAY

Sections of Missouri were swamped by remnants of Hurricane Dolly Wednesday. Totals
included 3.05 inches at Lees Summit, 2.78 at Kansas City and 1.63 at St. Louis.

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

The heavens opened across a large swath of Illinois late Tuesday, unleashing
downpours that drenched western Illinois' Rock Island with 2 inches of rain. The
Chicago area -- needing rain -- didn't completely escape the thundery deluges. Late
evening Doppler radar scans tracked downpour-generating cloud towers that reached
heights of 41,000 feet.

Even taller Downstate storms, responsible for rainfall so heavy that flash-flood
warnings were necessary in Champaign County and for tree-limb-downing 65 m.p.h.
wind gusts across sections of LaSalle County, were scanned as high as 58,000 feet.

The storms originated in Kansas early Tuesday then swept into Missouri, where they
inundated an area near Memphis, Mo., in the northeast corner of the state, with 1.90
inches in just 30 minutes.

CHICAGO AREA FLIRTS WITH 90 DEGREES WHILE TRIPLE-DIGIT HEAT KEEPS THE SOUTH BROILING

Temperatures hit 89 degrees at Midway Tuesday but 90s weren't far away. Heat in the
Deep South and southern Plains included triple-digit highs -- among them 101
degrees at Memphis and 100 degrees at Little Rock, Ark.

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

The Chicago area is getting a bit dry, something that doesn't take long to happen this
time of year. Strong summer sunlight encourages the evaporation of the equivalent of
1.20 to 1.40 inches of moisture a week from plants and topsoils. This makes it
essential that rains fall regularly.
But, the big rains of late spring and early summer have exited. The last big rain to fall in
the immediate Chicago area occurred 10 days ago when 1.61 inches fell at O'Hare
Airport and 1.05 inches at Midway Airport. Though scattered thunderstorms may
produce isolated downpours Tuesday, coverage is likely to be limited.
The Southern Plains are being scorched by 105- to 110-degree temperatures. The high
at Wichita Falls, Texas, hit 110 degrees Monday while Dallas tied its record high of 105
degrees.

727 DAYS SINCE LAST 95-DEGREE-PLUS
It's been 727 days since Chicago's last 95-degree-plus reading, a steamy high of 97 on
Aug. 2, 2006. That long stretch could end this weekend if readings reach the mid-90s.

SOME POSITIVE BENEFITS OF DOLLY
Though Hurricane Dolly brought flooding and devastation to South Texas, it also
dumped a welcome 5 inches of rain on some Texas drought areas.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

It's a pattern that has been repeated here all summer. Every time hot weather attempts to
make an inroad into the Chicago area, debris cloudiness or cooling outflows from
thunderstorms keep temperatures down here.
Once again hot weather is headed east into the Midwest as brisk southwest winds are
slated to sweep into the city Tuesday.
The approaching air mass has produced 90s and 100s in the Plains and lower Mississippi
Valley in recent days, such as the 103-degree record-tying high Sunday at Shreveport, La.
Some recent computer model runs have pegged Tuesday's maximum temperature here
in the upper 90s, but values that high seem unlikely as a combination of leftover
cloudiness and rain-cooled air from overnight thunderstorms slow the warm-up.
TYPHOON FUNG WONG MAY DROP 3 FEET OF RAIN ON TAIWAN
Packing winds as high at 105 m.p.h., Typhoon Fung Wong made landfall on the
east-central Taiwan coast Sunday morning.
The storm is expected to bring as much as 36 inches of rain to the central part of the
island with up to 18 inches on its north and south ends, including the capital of Taipei.
--By Steve Kahn, WGN Weather Center Meteorologist

The last week of July in Chicago will certainly be summery -- with daily highs mainly in
the 80s and moderate levels of humidity along with some scattered showers and
thunderstorms -- but lacking the heat, as has been the case nearly all summer.
Nineties have been scarce in Chicago so far this year, with the tally of only three days
at O'Hare International Airport and five at Midway Airport to date -- far below the
typical 15 or 16 usually logged here by the end of July. Another one is possible on
Tuesday.
Hot weather remains anchored from the lower Mississippi Valley to the Southwest
where readings are reaching triple-digits daily. A variety of heat warnings and
advisories are posted for Sunday from Mississippi west to Texas and Oklahoma.
ATLANTIC BASIN QUIET FOR THE MOMENT
After a flurry of activity last week with Hurricane Dolly hitting far south Texas and
Tropical Storm Cristobal skirting the Northeast coast, the Atlantic Basin is currently
storm-free.
However, a well-defined area of disturbed weather about 800 miles east of the Leeward
Islands is moving to the northwest and could develop into Edouard, the season's fifth
named tropical cyclone, later in the week.
--By Steve Kahn, WGN Weather Center Meteorologist

Lake Michigan's water level has risen 8 inches above the same period a year ago. Once
just 6 to 12 inches above all-time lows, lake levels are up in response to the same
downpours that caused many area rivers to flood. The U.S. Army Corps of Engineers,
which monitors the Great Lakes, predicts the higher levels are to hold through the
coming months -- though, barring new waves of heavy rains, the biggest rises have
probably already occurred. Interconnected Lakes Michigan and Huron are unlikely to
change significantly in the next month.
The corps reports other Great Lakes have experienced increased levels as well, with
Lake Superior 16 inches higher than a year ago. The rise in Lake Michigan means the
lake has added approximately 3.12 trillion gallons since a year ago.
Blistering heat continues to grip the southern Plains. The heat has anchored northwest
jet-stream winds over the area, which have slowed the eastward expansion of hot air in
recent months.
ABNORMALLY COOL ALASKAN SUMMER: ANCHORAGE'S 6TH-CHILLIEST SINCE 1917
So far this year, Anchorage has seen only seven days where the temperature
reached 65 degrees. Their coolest summer on record (1970) recorded a total of 16 such
days.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

The country's most humid air sits over a large swath of the Midwest on Friday -- more
humid over sections of the Heartland than the perennially muggy Gulf Coast. That's not
an accident. The Midwest is home to much of this country's most productive cropland
and crops send moisture airborne through a process known as transpiration -- the
evaporation of water from the leaves of plants. Strolling by a mature cornfield, you'll
feel a surge of moisture. Dew points, the preferred measure of moisture among
meteorologists, are expected to reach the 70s later Friday in Chicago and could surge
to near 80 degrees in sections of Missouri and Iowa -- a level most often associated
with tropical rain forests.

Truly hot weather continues to be a surprisingly rare commodity this summer in
Chicago. The highest temperature to occur has been 91 degrees. Not a single summer
in the past 80 years (since 1928) has failed to produce a higher temperature.

DOLLY'S TORNADO-PRODUCTION SPARSE BUT ITS RAINFALL HAS BEEN PLENTIFUL

The remnants of Hurricane Dolly managed only two twisters Thursday -- surprisingly
few for a landfalling Gulf Coast tropical cyclone. However, rains have been prolific.
Laguna Madre, Texas, was hit by more than 16 inches of rain.

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

Hurricane Dolly, after days of ingesting humid, energy-rich Gulf air over bathtub warm
waters, roared onto South Padre Island in Texas with 100 m.p.h. winds at 1 p.m.
Wednesday. In so doing, it became the first hurricane to make landfall on the U.S.
mainland since Hurricane Humberto moved ashore on the Texas/Louisiana border Sept.
13, 2007. Dolly pounded south Texas with rain in amounts that reached 12.85 inches at
Harlingen by nightfall Wednesday. The storm's 80 m.p.h. gusts whipped Padre Island,
transforming adjacent Gulf waters into an angry caldron and producing extensive
damage from the area's beaches to the inland community of Raymondville. Rainfall at
Brownsville topped a half-foot making it the wettest July on record. Concern turned to
the potential for serious inland flooding as the storm moved deeper into the Texas Hill
Country.

SHIFTS IN LONGER RANGE COMPUTER RAIN FORECASTS BEING MONITORED

Earlier forecasts play up dry weather for Chicago, but the latest longer-range forecasts
are hinting at a shift to wetter weather here that could begin as early as late Sunday
with another round of precipitation next week.

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

Chicagoans haven't experienced daytime temperatures cooler than Tuesday's
77-degree high at O'Hare since July 4. These readings fall 7 or more degrees short of
84 degrees, a level considered normal this time of year, and come only two days ahead
of the 74th anniversary of the city's hottest official temperature on record: 105 degrees
on July 24, 1934.

The 2008 warm season has been noteworthy for its lack of extreme or extended heat.
While the city's 39 days of highs of 80 degrees or higher to date are close the
long-term (80 year) average of 43 at Midway Airport, the 2008 warm season has
produced only three days at or above 90 degrees at the official thermometers at O'Hare
and five days at Midway, well short of the 13 days which have occurred by July 23 on
average since 1928. Northeast winds continue off Lake Michigan on Wednesday
promising another day of very moderate summer temperatures.

DOLLY THE FIRST HURRICANE OF 2008 TO LAND ON U.S. TURF

Dolly, a minimal hurricane, crashes into the south Texas coast Wednesday. The 2008
hurricane season is really humming in the Atlantic Basin. Normally the fourth named
storm of the season occurs around Aug. 26 -- making Dolly more than a month early.

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

Heat and humidity are taking a midsummer break in the Chicago area after a stormy,
muggy weekend that brought as much as 2.8 inches of rain to portions of Will County
since Friday. While the Chicago area escaped with just some light rain Monday morning,
other parts of the state were raked by damaging winds. Gusts estimated at 90-100
m.p.h. killed one and injured nine just east of the Quad Cities while winds reached 75
m.p.h. at Momence, 65 m.p.h. at Marseilles and 60 m.p.h. at Bourbonnais. City
precipitation totals approaching 9 inches since June 1 are making this the wettest open
to meteorological summer since the benchmark flood year of 1993, but drier, cooler
and less humid weather is headed for this area as a buckling jet stream delivers a
Canadian air flow.

STRENGTHENING DOLLY HEADS FOR SOUTH TEXAS

Tropical Storm Dolly, packing 50 m.p.h. winds, is expected to strengthen Monday as it
traverses the bathtub-warm waters of the western Gulf. Dolly could become a hurricane
before it makes an expected landfall near the south tip of Texas Wednesday afternoon.

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

Despite several rounds of showers and thunderstorms that brought significant rainfall
totals to the metropolitan area, Chicagoans still had enough sunny and dry hours to
salvage some outdoor activities on a warm, muggy midsummer weekend.
The week ahead promises a respite from last week's hot and muggy conditions with
readings most days expected to top out with seasonable highs in the lower 80s coupled
with comfortable humidity levels.
After some lingering showers and thunderstorms move out of the area Monday, dry
conditions are expected to hold until Friday when showers may develop in a surge of
warmth and humidity ahead of an approaching cold front.

ATLANTIC BASIN QUITE ACTIVE
Even though Bertha has lost its tropical characteristics as it heads for Iceland after a
record 17-day trek through the Atlantic, it was still packing 70 m.p.h. winds Sunday
evening. (Bertha set a new record for the longest-lasting tropical storm in July.)
Elsewhere in the tropics, Tropical Storm Dolly appears headed for a rainy rendezvous
with far south Texas by the end of the week, while Tropical Storm Cristobal will lay a
swath of heavy rain as it skirts the Atlantic coast as it heads for Nova Scotia.
--By Steve Kahn, WGN Weather Center Meteorologist

A frontal system squirming through a very warm air mass loaded with moisture sets the
stage for more thunderstorms Sunday, Sunday night and Monday. This morning the
southern edge of a strong complex of thunderstorms moving east into central Lake
Michigan will pass over northeastern Illinois. Scattered downpours and possible severe
weather may be experienced in the Chicago area, especially to the north near the
Wisconsin line. Some sailboats in the Mackinac race could get caught in the
thunderstorms over Lake Michigan and bucking easterly winds the remainder of the race
to the Straits of Mackinac. The sun should break out over the metro area later Sunday
morning. Then heating will push temperatures back to the 90-degree level, triggering a
possible redevelopment of thunderstorms.

ANOTHER SURGE OF STORMS TONIGHT AND EARLY MONDAY

One last low-pressure disturbance is expected to ripple through northern Illinois
Sunday night and early Monday, driving the frontal system south beyond the Ohio River.
Heavy downpours may occur. Later Monday, the southern portion of high pressure
centered over Canada will push into the southern Great Lakes and Midwest, bringing
milder, less humid air to Chicago.

Acting on a moisture-laden atmosphere, heating by ample sunshine triggered widely
scattered thunderstorms across the Chicago area Friday afternoon, and the storms
continued into the evening hours.
While many areas went rain-free, other locations experienced very heavy downpours. A
weather observer in Arlington Heights recorded 3.26 inches of rain between 6:30 and 8:45
p.m., while in the late afternoon, an observer in Wilmington, just south of Joliet in Will
County, measured 1.90 inches in one hour. As a large heavy rain area developed and
persisted over northern Cook County, the National Weather Service issued a flash flood
warning at 8:45 p.m. for that area.
ADDITIONAL HEAVY RAINS POSSIBLE
With a frontal system acting as the stimulus, thunderstorms could trigger rainfalls in
excess of 2 inches at many locations in northeast Illinois Saturday through Monday.

--By Paul Dailey, WGN Weather Center Meteorologist

Thunderstorm "debris" cloudiness -- remnants of dissipating thunderstorms that
flared to our west Thursday -- has spread across the area overnight. It's a development
that might bring an errant shower or two to parts of the area -- but is more likely to
reduce the amount of sun blazing down on the area Friday, possibly preventing a fourth
day of 90-degree temperatures over much of the area. Highs Thursday fell just short of
90 degrees at O'Hare (89 degrees) but surged to 91 degrees for the third consecutive
day at Midway. Other area highs included 93 degrees near U.S. Cellular Field on the
South Side and 92 degrees at New Lenox and at Griffith, Ind.

The storms which erupted to Chicago's west Thursday over Iowa and Nebraska may
hold clues to the weather ahead here. Drenching thunderstorm rains, which fell at the
rate of 1.90 inches in just 35 minutes near Table Rock, Neb., and 1.76 inches at the
National Weather Service Office at Hastings in just 25 minutes, caused widespread
street flooding.

TROPICAL FORECASTERS MONITORING T-STORMS DRENCHING SOUTHEAST

Conditions favor possible development of a disturbance off the Florida coast.

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

A gush of cooler air, generated by downpours out of powerful Wisconsin
thunderstorms, raced into the city on 35 m.p.h. gusts late Wednesday, offering
Chicagoans a burst of heat relief. The storms spent the day traveling southeast across
the Badger State, unleashing 70 m.p.h. winds gusts at Sheboygan and more than 4
inches of rain near La Crosse, before swiping extreme northeast Illinois. At one point,
clouds within the storm cluster towered to more than 52,000 feet. The outflow's arrival
sent Chicago temperatures tumbling from the mid-80s to the upper 60s. The plunge
followed a second day of 90s -- including 94 degrees at Alsip and 93 at Lincolnshire.
O'Hare and Midway Airports recorded the third 90-degree readings of 2008 topping out
at 90 and 91.

Combined with muggy, Gulf Coast-level 70-degree dewpoints, heat indexes peaked at
97 degrees on the South Side and 96 degrees at O'Hare -- the year's highest.

WORRISOME ATMOSPHERIC COMBO COULD IGNITE BIG RAINS THIS WEEKEND
Winds converging along a southward sagging cold front in an atmosphere saturated
with more than 2 inches of evaporated moisture could set the stage for clusters of
downpour-generating t-storms this weekend in parts of the Midwest.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

The area's most persistent hot spell of the summer is under way and predicted to hold
into the weekend. The heat encompasses sections of 36 states and produced highs
approaching 100 degrees in Nebraska and Kansas. Here in Chicago, three -- and
possibly four -- additional 90-degree highs are on the way by Saturday. Temperatures
first reached 90 degrees at 1:50 p.m. Tuesday at Midway Airport and at 2.49 p.m. at
O'Hare -- only the second time this year the city's official thermometer has made it to
that benchmark reading. Other area highs included 93 degrees in New Lennox, Alsip
and Chicago's Lincoln Park and 92 degrees in Berwyn and Harwood Heights.

The heat accompanies the season's first build-up of ozone. The Illinois EPA's Chris
Price cautions those with respiratory ailments to avoid overexertion outdoors.

REPETITIVE T-STORMS THREATEN MAJOR RAINFALLS IN COMING DAYS IN THE WEST
AND NORTHERN MIDWEST

With the jet stream locked into its summer position paralleling the U.S.- Canadian
border, impulses are likely to ignite t-storms which travel over the same terrain
multiple times in coming days. It's a prime set-up for big totals in sections of the
Dakotas, Iowa, Nebraska, Minnesota and Wisconsin.

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

Strings of 90-degree days -- like those predicted here for the remainder of the
workweek -- have occurred in 98 percent of the city's summers since 1928. But, the
first of them typically occurs on or about June 7. That makes the hot-weather period
predicted to dominate the area almost five weeks late. As many as four consecutive
90-degree highs are likely to occur here by the end of the week, something that has
occurred on 53 of the past 80 warm seasons -- or nearly two-thirds of the time.

The rain-cooled outflow of thunder- storms has reduced temperatures in each of this
year's warm spells to date. But warming aloft is to "cap" the atmosphere in coming
days, reducing prospects of rainfall. Though a steep vertical temperature drop this
afternoon may support a few thunderstorms in the area, most storm development in
coming days is to shift north into Minnesota, Wisconsin and Michigan near the jet
stream, which has migrated to its typical mid-summer location.

NORTHERN ILLINOIS CORN NEARING WEATHER SENSITIVE PERIOD

Illinois corn is nearing its pollinating stage. Regular rain and moderate temps become
important during this period.

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

After warming into the mid-80s away from Lake Michigan Monday, the remainder of the
work week may well see a series of days hitting 90 degrees or higher.
Readings of more than 90 degrees in the northern and central Plains are poised to cross
the Mississippi River, riding strong west to southwest winds Tuesday. With the jet
stream forecast to remain along the U.S.-Canadian border, Tuesday through Friday may
be the first time in nearly a year that Chicago will experience four consecutive days of
90 degrees or higher. The last time this occurred was July 31 through Aug. 3 of last
year.
So far this year, the official observation site at O'Hare International Airport has recorded
only a single day with a 90-degree high, 91 degrees on June 12. Last year by this time,
Chicago had experienced 10 90-degree days.
RAINS MAY HOLD OFF UNTIL WEEKEND
So far this month O'Hare has received 2.05 inches of rain, more than half the monthly
normal 3.51 inches. Unless thunderstorms drift south out of Wisconsin Wednesday
night, the next best chance of rain will be late Friday and Saturday in advance of a cold
front. Because this system is expected to be slow moving, downpours of an inch or
more may be possible.
--By Paul Dailey, WGN Weather Center Meteorologist

A northwest flow aloft will bring a brief period of cooler, less humid air over northern
Illinois and Wisconsin through Monday. However, the primary jet stream then moves back
north, establishing a strong west-east flow along the U.S.- Canadian border. This setup
will allow warmer and more humid air to surge back into the Midwest on the nose of
strengthening southwest winds. For three straight days, Tuesday through Thursday,
Chicago's highs will most likely exceed 90 degrees, while readings at night will hold just
above 70 degrees. Should these conditions occur, daily heat indexes will peak in the
mid-to-upper 90s, with little respite at night.

Temperatures across Chicago's south and southwest suburbs surged above 90 degrees
Friday. Highs there included 92 degrees at New Lenox and Markham, and 91 degrees at
Alsip and Griffith, Ind.
But the rain-cooled outflow from a diminishing cluster of thunderstorms sent easterly
lake breezes across much of Cook and Lake Counties in Illinois and into southeast
Wisconsin -- again sparing that portion of the Chicago area a 90-degree temperature.
New waves of thunderstorms were predicted to sweep the area overnight into this
morning. They come on the heels of five separate thunderstorm clusters the past two
days -- the most dramatic of them responsible for Thursday evening's widely observed
and photographed "shelf clouds."
Saturday's storm threat is the product of an approaching cold front that spawned at
least eight twisters in Minnesota -- some from 58,000-foot-tall thunderstorms.
RECORD RAINS SWAMP TUCSON
Monsoon-type rains hit the Southwest on Friday, scuttling the extreme heat of recent
weeks there while dropping 1.66 inches of rain on Tucson, Ariz. -- that city's
11th-wettest single calendar day in July.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

A powerful squall line -- at one point racing southeast at 60 m.p.h. and generating 700
cloud to ground lightning strikes every 10 minutes -- arrived with eye-catching fury
late Thursday. Downpours accompanied by wind gusts as high as 75 m.p.h. swept
Janesville, Wis., then moved on to north suburban Wheeling (63 m.p.h.) and McHenry
County's Lake in the Hills (60 m.p.h.). Some trees were downed primarily across the
northwest suburbs. The evening squalls began 600 miles to the northwest at around 6
a.m. Thursday in North Dakota. The southeastbound and persistent line of storms,
referred to by meteorologists as a derecho, produced damage over four states --
lambasting the Twin Cities around lunchtime and downing trees in the Madison, Wis.,
area mid-afternoon. Hail up to 3 inches in diameter bombarded Winsted, Minn. The
storms came on the heels of a nearly stationary cluster of storms responsible for hours
of lightning and rain centered on Lee County west of Chicago, where as much as 4.75
inches of rain fell at Sublette and 3.50 inches at Amboy.

MERCURY HEADED FOR 93 DEGREES THEN NEW STORMS TO HIT

New, potentially powerful storms develop in the wake of Friday's 93-degree heat late
Friday night.

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

Air conditioners will be humming Friday as some of the year's hottest temperatures and
a fresh surge of muggy Gulf air bear down on the Chicago area. A thermometer high of
91 degrees would equal this year's highest reading to date while a 93-degree high
would qualify as the Chicago area's hottest since a 94-degree reading on July 9 last
summer. The elevated temperatures originate from a vast reservoir of hot air which has
broiled the West in record-breaking triple-digit heat for days. Among Wednesday's
records in California was the 113-degree high at Redding, 110 degrees at Ukiah, 108
degrees at Sacramento and 107 degrees at Stockton. The addition of moisture as the
heat reaches Chicago threatens to push heat index readings into the 95-100-degree
range. Hurricane Bertha strengthened far at sea in the Atlantic on Wednesday and
threatens to attain Category 3 winds Thursday.

62% OF CHICAGO'S HOTTEST DAYS TYPICALLY ARRIVE AFTER JULY 10

Despite the lack of heat thus far this summer, history suggests that 62 percent (15
days) of Chicago's 90-degree or warmer days occur beyond this date.

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

Meteorological Summer 2008 has moved into its 6th week with an overall temperature
surplus (about 1.5 degrees) but with its surprising lack of truly hot days still intact. It's
single 90-degree high ranks it with only three other summers since 1928 with so few
90s this late in the season. The warm season to date has registered only 28 days in the
80s -- a 28 percent reduction from the 39 days recorded a year ago. Tuesday's
85-degree high temperature and steamy 70-degree Gulf Coast-level dew points ignited
several downpour-generating late afternoon thunderstorms. In Oak Brook, one
downpour from a towering thunderhead, scanned by area radars at 40,000 feet high,
unloaded 0.68 of an inch of rain in 50 minutes. Midway Airport was hit with 0.25 of an
inch in just 14 minutes.

Hurricane Bertha encountered wind shear -- shifting wind direction and speeds with
height -- which stole a bit of the storm's punch. Sustained winds dropped to 85 m.p.h.
-- further weakening is predicted

WILDFIRE-RAVAGED CALIFORNIA SIZZLES WITH 110-DEGREE INLAND HIGHS

Temperatures hit 111 degrees at Lancaster and Paso Robles -- and 110-degrees at
Palmdale in California -- all records.

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

Thunderstorms rumble across parts of the Chicago area Tuesday morning. As on other
occasions in recent days, the storms strike an ominous pose as they gather in Iowa and
western Illinois then scatter and only selectively distribute their wind and rain once
here. Nowhere has this been more evident -- and for farmers and gardeners, more
frustrating -- than in Chicago's southern suburbs. There rain has been in short supply
this month. Lawns have gone brown in recent days and there have even been reports
that the leaves of corn plants have been curling, indicating stress from lack of
moisture. The irony is this has transpired at the same time rivers have flooded in the
northwest suburbs.

Monday evening's thunderstorms towered to 60,000 feet while pounding sections of
Iowa and Wisconsin with 70 m.p.h. winds and heavy rains.

BERTHA ONE OF 13 'MAJOR' EARLY SEASON HURRICANES TO FORM SINCE 1851

Hurricane Berth's winds strengthened to 115 m.p.h. late Monday, making it a Category
3 storm. It becomes one of only 13 early season hurricanes to attain "major" (Category
3) status.

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

A slow-approaching cold front will allow extended warmth and humidity punctuated by
frequent showers and thunderstorms over the same areas recently hit by copious rains
and flooding. There will be a risk of severe storms, but renewed flooding could be the
greatest concern as heavy downpours from some of the stronger storms may leave
many locations across southern Wisconsin and northern Illinois with rainfall totals in
excess of 2 inches before rains end with an expected cold frontal passage Tuesday.
As the southern edge of a cooler, less humid Canadian high-pressure region pushes
into the Midwest, the band of heavy rains should drift into parts of Missouri, Oklahoma,
Arkansas and Tennessee Wednesday and Thursday. Humid southerly flow and more
thunderstorms return to the Chicago area later Friday and Saturday.

--By Paul Dailey, WGN Weather Center Meteorologist

As cool Canadian high pressure recedes to the east, southerly winds return to Chicago,
bringing warmer and noticeably more humid air back into the area. An approximate
two-day period of mid-summer-like heat, humidity and thunderstorms is expected to
begin later tonight. As a cold front approaches from the west, strong storms with heavy
downpours become more likely later Monday into Tuesday. Monday-Tuesday rainfall
totals could easily exceed two inches at many metro area observation points. The
southern portion of cooler less humid Canadian high pressure should hold over the
Midwest Wednesday and Thursday, with a shift in the jet stream flow allowing an
increasing southerly flow and the return of warm humid air next weekend.

--By Paul Dailey, WGN Weather Center Meteorologist

TROPICAL STORM BERTHA COULD BECOME HURRICANE THIS WEEK

The summer's warmest days typically follow in the weeks just beyond July 4. But you'd
never know it from the weather of recent days. Void of the stifling humidities so typical of
summer, the dry air of recent nights has permitted temperatures to drop quickly to levels
more typical of a month earlier. Friday opened with a 52-degree official low at O'Hare --
just two degrees off the 1980 record low of 50. Friday night's temperature decline was
predicted to yield 40s in far west suburban locations a second consecutive night.

Warming takes hold the remainder of the holiday weekend. The same air mass
responsible for a 102-degree high in Billings, Mont., and Denver's 97-degree peak
reading Friday is expanding eastward. Southerly winds within it are to tap Gulf moisture
in the next two days. In absolute terms, the amount of moisture in the air on Friday
here will quadruple by Monday. Its moisture is expected to fuel some clusters of
thunderstorms.
LAKE MICHIGAN STILL RISING
The Army Corps of Engineers reports Lake Michigan's water level is now 7" above a year
ago. That means the lake now holds 2.73 trillion gallons more water than it did the
same time last year.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

While hot weather aficionados long for a dose of 90-degree temperatures, it's hard to
complain about Friday's weather. The gusty northeast winds responsible for readings
more typical of May or September during evening fireworks displays Thursday have
departed. Light east winds linger Friday, but will travel a fraction of the distance over
chilly lake water before reaching the city. That's likely to limit shoreline highs to the
upper 60s and low 70s for the Taste of Chicago, an improvement from Thursday's low
60s there.

Thursday's 71-degree official high at O'Hare ranks as the city's chilliest July 3 in 45
years. Not since a 67-degree high in 1963 has it been cooler.

Storms that drenched Chicago's northern suburbs late Wednesday went on to produce
record early morning rains in Michigan. Grand Rapids was hit with 3.18 inches -- the
third wettest daily July tally on record.

IT'S THE DAY EACH YEAR WHEN EARTH IS FARTHEST FROM THE SUN
July is Chicago's warmest month. But it's also the month Earth is farthest from the sun.
At 3 a.m. Friday, Earth was as far from the sun as at any point in the year -- what
astronomers call aphelion.

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

Chicago's north and northwest suburbs suffered a direct hit by powerful thunderstorms
late Wednesday, with flooding and wind-whipped downpours even as lightning arched
earthward up to 1,300 times in just 10 minutes. Tree limbs snapped from Crystal Lake
in McHenry County into sections of southern Lake County while motorists scrambled
for the shoulders of area roads as visibilities diminished in the blinding deluges. Gusts
hit 60 m.p.h. in far northwest suburban Lake in the Hills and 50 m.p.h. at Long Grove
while hails measuring 0.5 to 1 inch in diameter peppered Arlington Heights and
Algonquin. In Barrington, 2.10 inches of rain came down in just 30 minutes sending
temperatures diving 20 degrees.
After radar scans measured cloud tops which reached to 55,000 feet. A second wave of
storms, erupted late Wednesday evening from towering 49,000-foot clouds.

CITY OFFICIALS DECLARED A SWIMMING BAN AS LAKE LEVELS GYRATED

Wednesday's fast moving thunderstorms produced at least two seiches Wednesday
afternoon and evening. Seiches occur when thunderstorms set up gyrating lake levels.
Water levels shifted as much as 2 feet in Wednesday's seiches.

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

A potent weather situation threatens to come together Wednesday afternoon and
evening -- one which threatens downpours and lightning-generating thunderstorms
accompanied at some locations by potentially powerful wind gusts. NOAA's Storm
Prediction Center has Chicago and surrounding areas of the Midwest outlooked for
possible severe weather. A cold front crashing southward on powerful northwest
jet-stream winds sweeps into humid, near-90-degree air -- an environment in which
atmospheric levels soar. It's this energy which powers t-storm winds and with nearly 2
inches of water evaporated in the atmosphere, the specter of local rainfalls of 1-3
inches isn't out the question in the hardest hit sections. It confirms a climatological
trend that has been observed in many Julys. Measurable rains become less frequent this
time of year -- occurring an average of 9 times per month. But the rains that fall can
be much heavier -- producing quick 1-2 inch tallies.

71% OF CHICAGO 90+-DEGREE DAYS OCCUR BEYOND THIS DATE

While hot weather's been in scarce supply this year, the area has typically recorded 7 of
the 24 days of 90-degree temps by July 2. That means summer is only getting going
with 71 percent of the areas's 90s to come.

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