July 2006 Archives

Stifling heat and extremely high humidity grip Chicago Tuesday, threatening the hottest open to an August in nearly two decades and a run on 100°—including a second consecutive record-tying (or breaking) high. The heat is so intense that an automobile, air conditioned to 83° and parked outside the National Weather Service office in Sullivan, Wisconsin, warmed to a lethal 119° in just 10 minutes Monday, underscoring the danger of leaving children or pets for even brief periods when the car’s been turned off.
Sunburns occur more quickly in weather this hot, warns dermatologist Dr. Bryan Schultz. And, allergy sufferers suffered through the year’s highest mold count of 57,771 (spores per cubic yard) Monday, the product of elevated humidities which foster mold spore formation.
Monday’s 99° high at Midway and O’Hare was 16° above normal and the hottest July close here in the 61 years since 1945.
-Tom Skilling-WGN-TV Meteorologist

The high heat phase of Chicago’s late-July heat wave was put on temporary hold Sunday as unexpected thunderstorms clipped the city, bringing a midday serving of clouds and cooler air. Highs fell short of anticipated readings in the upper 90s but still managed to reach 90º, extending the current string of 90º-plus days to three with three more expected before the heat wave breaks on Thursday.
The hot air should move into Chicago in earnest Monday and Tuesday with readings expected to top out around 100º, threatening the record highs for both days. Nightfall will offer little relief with readings in the city likely to remain above 80º both nights.
Clouds and showers should temper the heat a bit on Wednesday, but real relief won’t arrive until Thursday as northeast winds finally usher in low-80º air with comfortable humidity.
--By Steve Kahn, WGN-TV Weather Center

Kurt of Harbert, Mich., (10 miles north of New Buffalo) sent us this great picture of Sunday's thunderstorm clouds. "This is what today's storm looked like before it rolled through," Kurt said. "The photo was taken from our deck looking north in Harbert."

Thanks Kurt!

Two consecutive 90º+ days are already on the books and four more are expected as the city braces for what may turn out to be its most intense heat wave in 11 years. After Friday’s official high of 93º and Saturday’s 94º, the heat is expected to kick up a notch Sunday through Tuesday, with afternoon highs forecast to peak around 100º. The intense heat will be coupled with tropical-level dew points in the 70s that will raise heat indexes to dangerous levels around 110º.
Chicago has not broken or tied a summer record high since the city’s deadly 1995 heat catastrophe, but that may change as some of the forecast high and low temperature values challenge existing records—some of them dating back more than 90 years.
Chicago is finally getting its share of the heat that’s been baking the Plains and West for weeks now. Many record highs were established Saturday, including 111º in Pierre and 108º in Mitchell, both in South Dakota.
--Steve Kahn WGN-TV Meteorologist

The blisteringly hot air mass which is to tighten its grip on Chicago in coming days pushed 100s into northwest Wisconsin and Minnesota Friday—and may send readings within striking distance of 100° over parts of the Chicago area Sunday through Tuesday.
Portions of Duluth, Minn., more than 400 miles northwest of Chicago on Lake Superior, registered a high of 102° Friday while nearby Washburn, Wis., broiled at 101°—readings 25 degrees above normal. Official weather records in Duluth date back to the 1880s and include only three 100°-plus highs!
California’s mounting heat-related death toll reached 141 late Friday even as temperatures retreated from extreme levels for the first time in nearly two weeks. But the temperature rollback across much of the West is merely the by-product of an eastward shift in the dome of hot air.
Sixteen states reported 100s Friday. Temperature records were shattered in six of them—among them a 111° high at Pierre, S.D.
--By Tom Skilling, WGN-TV Meteorologist

Tornadoes all too often assemble beneath "wall clouds". A wall cloud is the isolated lowering of a thunderstorm's cloud base often in the southwest quadrant of such a storm and frequently situated within or close to a rain-free region at the back of the storm. These dramatic wall cloud photographs were captured by John Denk during Thursday evening's severe thunderstorms, dramatically illustrating why trained spotters across Chicago's southern suburbs were concerned about possible tornado development. John reports the wall cloud was, quite ominously, rotating. Tornadic circulations have been known to occur beneath wall clouds even before a complete funnel is visible. This wall cloud was spotted and photographed by John near 177th and Central Avenue just east of Tinley Park. Many thanks to John Denk for sharing these shots with us!
--By Tom Skilling, WGN-TV Meteorologist

Photos courtesy of John Denk

The thunderstorm’s awesome rain-generating capacity was on display over parts of the Chicago area late Thursday, fueled by daytime heating and an enormous supply of moisture. The explosively unstable atmosphere produced by surging temperatures triggered the rainy storm clusters. While O’Hare and Oak Brook were teased with just a trace of rain, converging ground-level winds along a weak lake-breeze front across Kendall and Will Counties appeared to focus repetitive downpours on Joliet and Chicago’s southern suburbs. A lightning-punctuated cloudburst swamped one section of Joliet with 6.13" while a nearby weather observer measured 5.50" in only 90 minutes. Northern suburbs weren’t completely spared. Mundelein in Illinois’ Lake County was hit with 1.70".
Funnel clouds and tornadic wind circulations detected by Doppler radar prompted tornado warnings, though no touchdowns were confirmed by late evening.
-Tom Skilling

The Chicago Tribune's John Smierciak, on his way back from covering the Bear's training camp in south suburban Bourbonnais, photographed these storms over farmland north of Beecher, Illinois. They are part of storm clusters which produced an unofficial rainfall of 5.50" in Joliet in just 90 minutes time!


PHOTO COURTESY: John Smierciak

This was the ominous scene in Round Lake Beach in Lake County this afternoon as downpour-generating t-storms erupted as photographed by Pam Sobieski. Radar cloud top scans indicated cumulonimbus clouds have grown to heights of 50,000 ft. this afternoon. To the south, tornado warnings were issued in response to numerous funnel reports—among them in Orland Park, Joliet, Shorewood and Minooka—and Doppler indicated tornado circulation signatures. Rain was torrential under the heaviest cells totaling 1.88" in 45 minutes in Joliet. Doppler precipitation estimates indicate several corridors of 1-2" of rainfall. But storms weren't universal. Estimates of areal rain coverage suggests 20-30% of the Chicago metro area has been visited by the storms. A severe t-storm
watch covers the entire area until 11 p.m.

PHOTO COURTESY: Pam Sobieski

It's not often lightning strikes as dramatic as these are captured in photographs. These photos were shot in Harvard, Illnois back on Thursday, July 20. Powerful storms, which swept Mc Henry County, unleashed these cloud to ground strikes captured by Michael Janesak. Many thanks to Michael for allowing us to post these here—and many thanks to Michael's co-worker Mary Davis who first called these shots to my attention!--Tom Skilling

PHOTOS COURTESY: Michael Janesak

The thick haze and mugginess of Thursday’s opening hours signal an atmosphere awash in tropical moisture. The haze may be just enough to limit warming a few degrees Thursday, holding a number of area highs just shy of 90°. Daytime heating is to coax the moist air to produce isolated t-storms.
Real heat hits this weekend. This year’s second extended string of 90s appears all but certain to produce highs above the 97° peak set Saturday, July 15.
Powerful t-storms spawned three twisters in central Illinois just after 7 p.m. Wednesday. One in Vermilion County downed trees, destroyed a tool shed and damaged several buildings. Parts of Champaign County were inundated by 1-3” of rain.
The 2006 hurricane season is running well behind a year ago. Only two named systems have occurred compared to 7 a year ago—including two Category 4 (131-155 m.p.h. winds) hurricanes.
-Tom skilling

A new round of summer heat looms. The first in what may end up a string of six consecutive 90s appears poised to arrive Thursday afternoon. Building moisture levels in the days ahead promise to make the impending hot spell a muggy one. Just how high temperatures ultimately go will depend, as always, on wind direction, the extent of thunderstorm formation (or the lack of it) and just how much sunshine occurs.
Some clusters of thunderstorms combined with Wednesday’s widespread cloudiness restrain warming. Highs hold short of Tuesday’s 90° peak at O’Hare and 91° at Midway. It marked the 10th time this year the mercury has reached or exceeded 90° at the South Side site—only 43% last year’s 23 Midway 90s to date.
Past years with similar 90° counts to date have gone on to produce an average of nine additional 90° readings.
-Tom Skilling

Waves of thunderstorms—some hail-bearing—pounded a swath of central Wisconsin repeatedly Monday. It’s a pattern likely to repeat with some regularity in various sections of the Midwest in coming days as humidities build.
Isolated storms, the leftovers from Monday’s assault to the north, threaten an appearance in parts of the Chicago area as Tuesday begins—then may re-fire with daytime heating over 20-30% of the region in Tuesday’s muggy near-90° air. Better storm coverage—up to 70% of this area—may be visited by sometimes downpour-bearing storms Wednesday.
Golf-ball size hail pounded Thorp, Wis., in Clark County to the east of Eau Claire, for 10 minutes Monday. And a “wet” microburst, the blast of damaging winds which spreads radially as air after crashing to earth in t-storm downpours, generated 58 m.p.h. straightline wind gusts which damaged two aircraft on the east side of the Green Bay’s Austin Straubel Airport.
--By Tom Skilling, WGN-TV Meteorologist

This picture of an atmospheric phenomenon known as a circumhorizontal arc (sometimes called a fire rainbow) was taken in the northern suburbs Saturday afternoon July 22. It is caused by the refraction of light through the ice crystals in cirrus clouds. It only occurs when the sun is high in the sky, 58º or higher above the horizon, so at Chicago's latitude it can only occur from about mid April to late August.

The American Meteorological Society's Glossary of Meteorology explains that the most colorful circumhorizontal arcs occur when the sun is at an elevation of about 68º above the horizon. On Saturday afternoon July 22, the maximum solar elevation was 68º!

Photo taken by Jodi Kahn

This past weekend brought Chicagoans a welcome respite from last week’s heat and humidity, but all that is about to change as the city braces for a week highlighted by heat, humidity, and frequent showers and thunderstorms. Highs should approach 90º on Monday but with only moderate humidity levels. By Tuesday, dew points should reach the uncomfortable 70º threshold, where they should remain for the rest of the week. Excessively high temperatures are not expected as cloudiness and an almost daily occurrence of showers and thunderstorms should keep daily highs between the upper 80s and lower 90s. That was not the case last year when the mercury soared to 102º on July 24, bringing the city its first triple-digit high since the heat wave of July 1999.
Intense heat continues to scorch the West as temperature records tumbled. Fresno, Calif., reached 113° Sunday. Pasco in south-central Washington sizzled at 112°; nearby Yakima reached 109°.
--By Steve Kahn, WGN-TV Weather Center Meteorologist

"WOKE LAST NIGHT TO THE SOUND OF THUNDER"

Talk about coincidences! Back in the 1970s and 1980s it seemed that Chicago was frequently in the path of numerous derechos—fast moving clusters of thunderstorms that formed during the evening in the northern Plains or Upper Mississippi Valley on the northern edge of a dome of intensely hot air. These storms would then move into the Chicago area at speeds approaching 60 m.p.h., arriving during the pre-dawn hours with torrential rain, hail and damaging winds. Detroit rocker Bob Seger's 1976 song "Night Moves" is one of my all-time favorites. The last verse of the song begins with the the line "I woke last night to the sound of thunder" and it has always reminded me of those late night derechos.

Well, Bob Seger has been on a long hiatus from the music scene and it's been a long time since late-night derechos have swept into Chicago. After more than 10 years Seger is finally releasing a new CD this September, and as if to mark the occasion, around 4 a.m. last Thursday morning as storms swept into the Chicago area, I once again "woke to the sound of thunder".

The last verse of "Night Moves" by Bob Seger

I woke last night to the sound of thunder
How far off, I sat and wondered
Started humming a song from 1962
Ain't it funny how the night moves
When you just don't seem to have as much to lose
Strange how the night moves
With autumn closing in..

(Night Moves by Bob Seger Capitol Records 1976)

HAIL IN CAROL STREAM

Thunderstorms developed in Wisconsin on Saturday afternoon and moved south into northeast Illinois during the early evening hours. Several of the storms became severe producing penny-sized hail (.75") along with heavy downpours. Robert Guico of Carol Stream was kind enough to send us these photos as a barrage of pea-sized (.25") covered the ground at his home.

Photo by Robert Guico

Photo by Robert Guico

A gorgeous Saturday across the Chicago area turned nasty in the evening as thunderstorms moved south out of Wisconsin. The Fox Valley was hardest hit as penny-sized hail fell in Crystal Lake, Wheaton and West Chicago. Local downpours produced radar estimates of more than 2” of rain. The heat-driven storms faded quickly as sunset approached.
More thunderstorms should frequent the Chicago area in the upcoming week as another surge of heat and humidity arrives. Temperatures should approach 90º by Monday and fluctuate around that level the rest of the week, while 70º-plus dew points will give the air a muggy feel.
Intense heat continues to bake the West as records tumbled Saturday from Texas to Oregon. Downtown Los Angeles sweltered at a record 101º while Burbank’s 112º came within one degree of its all-time high. Even Stanley, Idaho, known for its lowest-in-the-nation temperatures, tied its record high for July 22 with a 92º on Saturday.
--By Steve Kahn, WGN-TV Weather Center Meteorologist

Some rain-starved areas of northern Wisconsin may be visited by thunderstorms Saturday as rising temperatures encourage air to ascend and cool. This process leads to afternoon thunderstorm formation Saturday and could be enhanced as a pocket of powerful jet stream winds dives into the region from the northwest. Recent days have seen copious rainfall in parts of the Chicago area; however, much of northern Wisconsin, Upper Michigan and Minnesota have been dry. Lake and river levels are down, and some rain there would be welcome. Since June 1, Rhinelander, Wis., has recorded rainfall 5.68” below normal.
Timing will be everything in terms of any impact of these scattered storms on the Chicago area. Clouds may increase slowly from the northwest, and scattered storms could reach north and west sections of the metro area later today—a few could even reach the city. Daytime heating may brew additional storms Sunday afternoon and early at night.
--By Tom Skilling, WGN-TV Weather Center Meteorologist

Extreme drought gripped the area a year ago. Lawns were brown, crops were struggling and sprinkling bans loomed. To be sure, the recent rainfall bonanza has bypassed some parts of the state. But, Chicago isn’t among them, and the 7.52” of rain on the books since the beginning of meteorological summer (June 1) dwarfs the 1.49” which had fallen by this date a year ago.
For up to eight hours Thursday beginning at 4 a.m., a 30-50 mile-wide corridor extending from Rockford and McHenry county across Chicago and into northwest Indiana was swept by waves of thunderstorms—repeatedly. The phenomenon, known as training, generated 2.05” at O’Hare—the site’s largest calendar day rain total since Aug. 1, 2003 (2.24”). That’s over a half an inch more rain than had fallen to date during the entire summer season a year ago. Other heavy totals Thursday included 2.54” at Schaumburg, 2.45” at Algonquin and 1.79” at Mt. Prospect.
--By Tom Skilling, WGN-TV Weather Center Meteorologist

Midway Airport storm photo courtesy of Dom Mancuso

Waves of powerful thunderstorms, which produced tree-downing wind gusts and flooded Chicago and a northwest-to-southeast corridor 30-40 miles across from Rockford to Chicago to the Indiana Dunes and Valparaiso areas of northwest Indiana, knocked power out to tens of thousands in the Chicago metro area. Trees were down in Carpentersville, and water was standing in portions of Chicago in the storm's wake.

Cloud tops towered as high as 52,000 feet Thursday morning. The heaviest rain totals came from Boone and McHenry counties. For some of the most heavily affected areas there, it was the third round of storms to produce flooding in the past two weeks. The heavy, lightning-peppered rains occurred as thunderstorms "trained" (reoccurred over the same area) over the areas with the largest rain totals, subjecting these areas to wave after wave of downpour-generating thunderstorms. In Arlington Heights, my colleague meteorologist Steve Kahn reports lightning and thunder lasted eight hours there and extended through midday, having started around 4 a.m--an observation reported to us from Schaumburg as well. Chicago's official rainfall at O'Hare topped out at 2.05" with Midway Airport recording 1.17".

Some preliminary rainfall totals through midday Thursday include:
Algonquin 2.30"
Arlington Heights 1.57"
Midway Airport 1.17"
O'Hare Airport 2.05"
Schaumburg 2.54"
Wilmington (Will County) 0.90" (6" reported since June 1)
Mundelein 1.60"
Parts of McHenry County received 3-4" rain tallies, and the same corridor of rain hosted 5-6" Doppler estimate rainfalls to the northwest in sections of south-central and southwest Wisconsin.
--By Tom Skilling, WGN-TV Meteorologist

A fast-moving cluster of violent thunderstorms—what meteorologists refer to as a derecho—swept south across Illinois Wednesday afternoon and evening with cloud tops as high as 65,000 feet, raking portions of western Illinois as well as the St. Louis metropolitan area with wind gusts in excess of 90 m.p.h. Damage to trees and power lines was widespread, and windows were blown out of many buildings.
More than 40,000 baseball fans huddled in the interior of St. Louis’ brand-new Busch Stadium as the storm front swept the area with the high winds blowing windows out of the press box, ripping the field tarp and downing trees outside the stadium. Temperatures in St. Louis peaked at a steamy 100º before the storms hit but plunged more than 25 degrees to the mid 70s in their wake.
It was but the opening salvo of a prolonged barrage of thunderstorms that was expected to last into Thursday morning.
--By Tom Skilling and Steve Kahn, WGN-TV Weather Center Meteorologists

While most people are aware of the wildfires associated with the hot weather out West, there's also a raging wildfire burning in the Boundary Waters region of northeast Minnesota. Winds have pushed the smoke plume all the way to the Upper Peninsula, according to John Dee of Michigan’s Keweenaw Peninsula. "We have been smelling the smoke from time to time, basically whenever there is a west-northwest wind," Dee said.

Below is a satellite photo of the smoke plume. In addition. here's a link to some recent dramatic pictures of the wildfire, courtesy of Barb Tuttle, Carol DeSain, Betsy Bowen and Dawn Ohmes.

For many, Tuesday’s temperature-slashing NE winds arrived not a moment too soon. Tuesday’s 83° was 12° below Monday’s steamy 95° thermometer reading. But, an even more impressive plunge in atmospheric moisture levels—clear in the dramatic dew point pullback from Monday’s 76° to late Tuesday’s 56°—really hit home for most area residents. The air here, from which 2” of evaporated moisture could have been squeezed Monday, held just 0.72” late Tuesday—only 35% as much! While downstate Illinois residents retired late Tuesday amid muggy 80° dew points and 90° evening temperatures, heat indexes threatened to surge into the dangerous 105-115° range Wednesday. By contrast, Chicago area residents were able to open windows Tuesday night and enjoy more normal nighttime cooling. Drier air retains less heat. But surging moisture Wednesday night threatens new t-storm clusters.
-Tom Skilling

The heat grew oppressive—even dangerous—Monday. No single summer day in the seven years since 1999 has generated a more stifling temperature/humidity combination. Mid-afternoon thermometer readings of 95° combined with stifling Amazon Valley-level 76° dew points—a level higher than at most weather reporting stations on the Gulf of Mexico—to produce a 109° heat index at O’Hare and 108° at Midway. At Northerly Island, where the dew point hit 80°, the heat index soared to 114°.
Had all that moisture been uniformly squeezed from the air Monday, more than 2" of rain would have fallen across the area. Late evening t-storms, some 12-miles tall, produced damage and power outages in Rockford amid their dazzling lightning displays. More than 3,200 cloud to ground strokes occurred in one 10 minute period late Monday within a 225 mile radius of Chicago.
-Tom Skilling

As hot and humid conditions persist into a second day, the National Weather Service continues the Excessive Heat Warning and the Illinois EPA continues the Air Pollution Action Day for Chicago. The approach of a cold front should increase the chance of thunderstorms—a few could be severe—later this afternoon and more likely tonight. These storms will bring needed rain and also cool things off a bit.
Northeast winds Tuesday will drop highs down into the “normal” mid 80s; but where it rained, sunshine will enhance evaporation, and the added moisture into the air will make it feel humid. A quick warm-up Wednesday will be cut off by the approach of a second cold front with more significant rains possible later that day and night into Thursday. Cooler, less humid conditions are in store Thursday-Friday.
More 100°-plus record highs were reported Sunday across the central Plains, including 113° at Valentine, Neb.
--By Paul Dailey, WGN-TV Weather Center Meteorologist

Temperatures should hit or exceed 100° around the Chicago metro area this afternoon. An official heat index between 105 and 110° is likely. Chicago has experienced a 110° heat index only once ( 114° on July 30, 1999) since the all-time record of 125° was set during the deadly 1995 heat wave. The Excessive Heat Warning takes effect at 1 p.m. this afternoon. The impact of the heat will be further enhanced by the mostly sunny skies—the sun will beat down on dark rooftops which will absorb and reradiate the heat into the buildings below.
The city has cooling stations and the emergency aid 311 telephone number for those in need of assistance.
Chicago sits on the eastern edge of 100° readings which reach back west into the Rockies and as far north as Bismarck, N.D. A 120° reading was observed near Usta, S.D. yesterday tying the all-time record high for that state.
--By Paul Dailey, WGN-TV Weather Center Meteorologist

The summer’s most intense, longest-lasting round of heat gets underway Saturday, threatening seven straight days of 90s. An eastward expansion of the superheated air mass behind the raging wildfires out West produced highs of 104° at Rapid City, S.D., and at Chadron, Neb., Friday—only the latest records to occur in the Plains in recent weeks.
Though temperatures here become hot Saturday afternoon, light lake breezes and moderate humidities (compared to what’s on the way in coming days) may spare sections of the city the truly blistering level of heat predicted Sunday. That’s when peak afternoon heat indexes may approach 110°. Readings that high mean overexertion can bring on heat exhaustion or even heat stroke—a condition in which body temperatures surge, and dizziness or unconsciousness have been known to occur. The predicted high of 100° Sunday would mark only the 85th time a triple-digit reading has occurred at Midway Airport since 1928.
--By Tom Skilling, WGN-TV Meteorologist

Alaskans refer to Mount McKinley, North America's tallest mountain at 20,320 feet, by its native name: Denali. The mountain, in this photo forwarded to us by Tom MacPhail, was "out" (visible) in all its glory this past weekend. We're looking at Denali and the Alaska Range from a distance of about 30 miles as taken a little over two hour's drive north of Anchorage.
-- Tom Skilling, WGN-TV Meteorologist

The area’s most prolonged hot spell looms. Clouds, clusters of thunderstorms and winds off Lake Michigan, while unlikely to temper the muggy “feel” of the air Friday, are likely to hold most area temperatures just shy of 90°. Temperatures are to take off in Saturday’s unlimited sunshine. Mid 90s are likely in all but immediate lakeshore areas by afternoon—readings Sunday and Monday may flirt with 100°. The heat marks the beginning of seven consecutive days of 90s—2006’s longest to date. Lake breezes Saturday and Tuesday limit daytime highs a bit but have minimal impact on temperatures. That’s because lake waters are warming. Great Lakes water temperatures Thursday reached the highest levels of the year. Though 1° cooler than a year ago, Lake Michigan’s satellite observed 68° average Thursday (Chicago’s shoreline reading was 73° near Navy Pier) and is more than 30°above early March levels.
-Tom Skilling-WGN-TV Meteorologist

July usually brings to mind images of “lazy, hazy days,” an adequate description for Chicago’s weather in upcoming days, but some major weather extremes have been July events. Chicago’s worst weather-related tragedy, the heat disaster of mid-July, 1995, claimed 700+ victims. On July 10, 1913, the temperature zoomed to 134º in Death Valley, Calif., establishing a U.S. heat record. Wisconsin’s all-time high, 114º, occurred at the Dells 70 years ago (July 13, 1936), and Indiana’s highest, 116º, was logged the next day (July 14, 1936) at Collegeville, 70 miles southeast of Chicago.
It’s summer here but July is the heart of winter at Vostok Station, Antarctica, which established a world record low: -129º on July 21, 1983.
In July, 1861, 366.14 inches of monsoon rain swamped Cherrapunji, India, setting a world one-month rainfall record that still stands (an amount ten times Chicago’s annual total).
-Richard Koeneman, WGN-TV Meteorologist

Tuesday’s rain totals varied widely across the area, but 1-2” doused some locations, prompting weather observer James Buckman of Bonfield, Kankakee County, to remark, “The farmers are smiling this morning. This is a million-dollar rain.”
Not only is July Chicago’s most thundery month, it is also the city’s warmest month. And history tells us that within July, the period from the 16th through the 29th is the city’s very warmest. A typical day during that time features an afternoon high in the middle 80s and an early-morning low in the upper 60s (Midway Airport data).
But, cool interludes are a frequently-occurring part of Chicago’s July climate. In fact, a few July days on which afternoon temperatures linger in the 70s (as happened yesterday and Monday) are a virtual certainty. In 78 Julys since 1928, every July except one (1955) has delivered at least one 70° day.
-Richard Koeneman, WGN-TV Meteorologist

The ingredients necessary for turbulent weather are falling into place and the atmosphere is poised to deliver heavy rain to the Chicago area today. Severe thunderstorms, too, are likely, and much of Illinois and Indiana lies within a broad area which the Storm Prediction Center has highlighted for potentially violent activity this afternoon.
The boundary between air masses of contrasting temperature often acts as a focus for thunderstorm generation, and such a boundary lies just to the south of the city area. While Chicago experiences daytime temperatures in the 70s, afternoon readings will top 90º in sunny locations downstate.
Moisture, also, is abundant. Dew point temperatures 70º+ lie just to the south of the city and storms tapping that juicy air will be copious rain-producers.
Finally, steering winds aloft are rather weak and thunderstorms will be slow moving, adding further to the rain potential.
-Richard Koeneman, WGN-TV Meteorologist

Somewhat cooler air dips into Chicago today and Tuesday, but it’s only a tease. In the atmospheric tug-of-war between today’s cooler air borne in by pleasant northeasterly winds and warm, humid air being pushed out, the warm air will yield briefly but ultimately triumph.
An atmospheric boundary (known to meteorologists as a front) that marks the transition zone between the cooler and warmer air masses will penetrate only to central Illinois by Tuesday morning, then stall and return north late Tuesday. Chicago’s daytime temperatures, cooling modestly only to the lower 80s today and Tuesday, climb well into the 80s midweek as warmer and more humid air returns. Then real heat and humidity arrive: 90º on Friday and lower or middle 90s over the weekend—and that might be only the beginning. The jury is still out, but computer models now suggest a lengthy period of hot weather, interrupted only by weak and modest cooling, lies ahead.
--By Richard Koeneman, WGN-TV Weather Center Meteorologist

After several days of pleasant temperatures, comfortable humidity and sparklingly clear air, summer weather more typical of July will characterize Chicago weather this week. That means heat, humidity and haze by day and noticeably higher nighttime temperatures as well.
The mercury will fluctuate through the 80s on most days through midweek, but readings push close to 90º on Thursday and then into the 90s on Friday and Saturday. A 90° high on Friday, should it occur, would mark only the sixth 90º-plus day this year.
In nine other cool-starting summers with only five days in the 90s through July 8 (Midway data), the remainder of those summers went on to produce an average of 14 more days at or above 90º, and therefore a full-year average of 19 days with 90º-plus temperatures—a value significantly lower than the long-term average of 24 days.
--By Richard Koeneman, WGN-TV Weather Center Meteorologist

Today’s afternoon readings in the middle 80s mark the return of summery temperatures to the area, and the highest value since the city logged 90º on July 1. Computer models indicate this is merely the first in a multiday string of warmer days that will ultimately carry the city’s temperatures into the lower 90s. Humidity, too, creeps up this weekend and becomes oppressive by midweek.
Today marks the 326th anniversary of an often overlooked weather event that stands as a U.S. meteorological milestone: the occurrence of the nation’s first confirmed tornado. A tornado touched down during the early afternoon hours of July 8, 1680, in Cambridge, Mass. The twister was filled with “stones, bushes, boughs, and other things,” as reported in “Significant Tornadoes,” an authoritative text by noted weather historian Thomas P. Grazulis. The tornado snapped many trees, unroofed a barn and killed one person.
-- By Richard Koeneman, WGN-TV Weather Center Meteorologist

We’ve come to expect blazing heat and oppressive humidity in a typical Chicago July, but you would never know it by looking at the temperatures and humidities that have prevailed across the city recently: three consecutive days with afternoon readings in the 70s coupled with pleasantly low relative humidity.
All of this has come to us compliments of a sprawling high pressure system that has delivered to Chicago and the Midwest fair, cool and dry Canadian air relatively devoid of pollutants.
The air mass, however, is “aging” and, starting today, its pleasant characteristics will give way to a gradual increase in temperatures and moisture in upcoming days—each day being incrementally warmer and more humid than the day before.
Showers and thunderstorms eventually return to the area, possibly by late Sunday.
-Richard Koeneman, WGN-TV Meteorologist

These pictures were shot on a hike this past Monday (July 3, 2006) through Portage Pass—which sits about 40 miles southeast of Anchorage and adjacent to the Portage Glacier. The weather was beautiful during this hike with my friend and meteorological colleague Tom MacPhail, who's currently an aviation forecaster at the National Weather Service Forecast Office in Anchorage and a long-time Alaska resident. Portage Pass can be home to some of south-central Alaska's most volatile weather, including driving rains and channeled high winds (70+ m.p.h.) and blinding, often horizontally-falling winter snows. Pilots use the pass frequently, but do so with a careful eye toward the weather. Though the weather was beautiful on this hike, a marine-layer overcast shrouded Whittier on the Prince William Sound side of the pass from sunny skies to the east. Terrain drives many weather changes in Alaska and the sharp weather shift on this relatively short hike was quite fascinating! Portage Pass sits between the port town of Whittier on Prince William Sound and the Turnagain Arm, an inlet off Cook Inlet that hosts "boar" tides—visible as a single wave sweeping up the inlet which can reach 12 feet in height on occasion when winds are just right—and which boasts the largest North American tidal swings (as much as 35 feet from high tide to low tide) outside Canada's famous Bay of Fundy. Turnagain Arm, known to channel its own powerful winds, extends some 45 miles from its source at Anchorage on the Cook Inlet.
--Tom Skilling

Photos: Courtesy Tom MacPhail:

Chicago’s feast of refreshing Canadian air continues for a third day today. On Wednesday, temperatures remained in the comfortable 70s, with nearly unheard of dew points in the 40s. Besides the delightful temperatures and humidity, visibility was especially keen. Chicago’s skyscrapers were clearly visible 25 to 30 miles out into the suburbs.
With time, the air mass slowly warms in the long days of intense July sunshine. Humidity and haze creep into the mix, as more normal summer weather returns on Friday. Thereafter, temperatures and humidity slowly climb, with a slight chance of t-storms returning by Sunday or Monday. For Tuesday and Wednesday, computer models suggest that an upper level disturbance invades from the southwest, with Gulf moisture and widespread rainfall. As a result, temperatures fall off here, while sizzling heat builds in Wisconsin and Minnesota.

A refreshing dose of cooler, drier Canadian air reached O’Hare Airport at 8:30 a.m. Tuesday morning, sweeping south of the region a few hours later. The effects were dramatic: Winds switched to the north, visibility sparkled and humidity began to drop. By afternoon, Chicago was reporting some of the nicest holiday weather in the country.
In the days ahead, this air mass inches eastward, passing Chicago Thursday night, and finally settles in the Southeast as the western extension of the Bermuda high by early next week. In summer, slow-moving Canadian highs tend to warm up, entrain humidity and haze, and eventually become the source of summer heat and humidity. As a result, temperatures and humidity should gradually warm with time. Fresh air with a lake breeze turns warmer and more humid over the weekend, and hot and humid with a chance of thunderstorms early next week.
--By Dennis Haller, WGN-TV Weather Center Meteorologist

Monday morning’s rain yielded to afternoon sunshine at Chicago, but the added moisture caused dew points to surge between 70°-75° by evening.
South and east of Chicago, strong thunderstorms erupted in late afternoon, prompting severe weather warnings south of Kankakee, and even a tornado in St. Joseph County in southern Michigan.
All of the turbulent, muggy weather comes to an end later today, with refreshing north winds and falling humidity by evening. The next few days that follow will be delightful. Wednesday and Thursday both feature a fresh lake breeze with comfortable temperatures and humidity.
Thereafter, the cool Canadian high pressure responsible for the pause in summerlike temperatures begins to moderate in the intense July sunshine.
As a result, temperatures climb a little each day, reaching 90° by next Monday.
-Dennis Haller, WGN-TV Meteorologist

Thunderstorms with some severe weather have failed to materialize over Chicago during the past few days despite favorable storm conditions.
Instead, thunderstorms have popped in all directions around Chicago both Friday and Saturday. Conditions remain favorable for thunderstorms Monday and showers until about noon Tuesday, so holiday plans later in the day should go off without a hitch, especially from Chicago northward.
By Tuesday night, cooler, drier air from Canada sweeps in, followed by several days of sunny skies and a refreshing afternoon lake breeze. Temperatures and humidity creep higher later in the week and into next weekend, but scorching July heat should hold off until the following week. Current models indicate a string of 90°-plus days seem likely in a week to 10 days from now.
--Dennis Haller, WGN-TV Weather Center Meteorologist

Saturday’s high temperatures topped out at 90° at O’Hare, 91° at Midway, and 92° at the lakefront, the fifth time this year Chicago crossed the 90° threshold. Normally, Midway’s seasonal total of 90° days would be 7 days by July 1, with O’Hare at 6 days. Sunday’s chance at 90° diminishes as the chance for clouds and thunderstorms increase.
An unstable atmosphere and nearby respectable summer jet stream team up for a chance of severe weather and heavy rain at Chicago. This severe weather threat covers a wide swath from Wyoming and Colorado eastward to the Atlantic seaboard right through Monday.
Chicago’s thunderstorm and rain threat finally diminishes early Tuesday as a strengthening cold front backed by refreshing Canadian air sweeps through in the morning, with the rest of the holiday rain free and with lowering humidity. Similar pleasant days continue right into next weekend.
-Denis Haller, WGN-TV Meteorologist