Meteorological Autumn
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For astronomers, autumn begins in three weeks at 11:03 p.m. Friday, September 22. That’s the instant the sun’s most direct rays fall on the equator—the so called autumnal equinox. From that point forward through winter, these direct rays will shift into the southern hemisphere allowing colder air to accumulate over sections of the northern hemisphere.
But, for meteorologists and climatologists, Sept. 1 appears a more natural demarcation between the summer and autumn seasons. From today (Sept. 1) through the coming three months, normal daily highs will decline from 78° to 40.
Meteorological summer 2006 closed at midnight, finishing 1.5° above normal—the 35th warmest summer of the past 136. The area received just 61% of its possible sun as a result of more than usual summer cloudiness—the most of any summer in 9 years. 67% is considered normal.
-Tom Skilling WGN-TV Meteorologist
August 2006 closes far differently than it opened. Though the month has averaged 74.3°—nearly 2.5° warmer than normal—it’s closing on a cool note. Thursday’s predicted 75° high is 24° below the blistering 99° reading recorded here on Aug. 1. The sizzling temperature was part of the summer’s hottest spell of weather and led to a number of heat related deaths. In stark contrast, NE winds around the southern flank of a sprawling Canadian high, sweep off Lake Michigan Thursday. It marks the 17th day this month to feature lake winds winds. No other August in the past 73 years (since 1933) has featured as many days with east or northeast winds here.
With the current pattern locked in place beyond Labor Day (next Monday), at least 12 consecutive days of 70s seem a good bet here by mid-next week, making the pre-autumn cool spell the areas longest in 12 years.
-Tom Skilling-WGN-TV Meteorologist
Autumn was in the air again Tuesday. October-level temperatures paid the Chicago area a visit for a second consecutive day. Midway Airport’s 69° high temperature was the coolest on an August 29 in 41 years—since a 66° high in 1965. The reading ranks among the three coolest for the date since weather observations began at Midway in 1928. The late summer “chill” is especially noticeable coming at the end of a season in which 61% of daily average temperatures have finished above normal.
By early next week, Chicago will have logged 11 consecutive highs below 80°—its longest pre-autumn cool spell in 12 years.
Late arriving reports on Monday’s deluge indicate even heavier rain totals than first reported across southern sections of the metro area. Among the heaviest totals were 3.50” at Hammond, Lansing and Munster, 3.13” at Park Forest, 3.32” at Morris and 2.84” at Rensselaer, Ind.
-Tom Skilling, WGN-TV Meteorologist
These Beverly Shores, Indiana damage photos further underscore the fury of last Wednesday evening's microburst-generating thunderstorm. These are but the latest images to illustrate the devastating effect of last Wednesday evening's 100+ m.p.h. wind-generating thunderstorm complex as it roared onshore in northwest Indiana from Lake Michigan. Curt Kendall has sent along these photos from Beverly Shores, Indiana along with the following e-mailed comments:
"On Wednesday evening (August 23), I arrived home in Beverly Shores at 5:45. I took out my leaf blower and started blowing leaves off the steps and driveway. It started to sprinkle. At 6:00 the tornado sirens went off, I thought it seemed strange. At 6:01, I turned on the TV and an emergency announcement said that a tornado was headed toward Beverly Shores and Pines, Indiana and it would hit at 6:05. By 6:05, the winds were over 100 miles per hour, the rain was falling horizontally. Trees started to fall. My stainless steel gas grill was picked up and thrown across the yard. By 6:10, the winds slowed and my neighborhood devastated."
Many thanks to Curt for sharing his harrowing experience in one of the worst storms to sweep any section of our area in some time.
PHOTO COURTESY: Curt Kendall
Jack and Kate Anderson share this spectacular August 28, 2006 sunset on their lake in Watersmeet, MI. Seldom, they tell us, is the lake so calm you have such a spectacular reflection of the sky visible!
PHOTO COURTESY: Jack and Kate Anderson, Watersmeet, MI
Wind-driven rain—well over 2" of it Monday across Chicago’s southern suburbs and one of this summer’s seven heaviest rainfalls—pushed August precipitation tallies across a large swath of the metro area to nearly five times higher than the same period a year ago. Monday’s 1.08" at Midway Airport brought the month’s total at the South Side site to 7.08"—the sixth greatest August rainfall on the books since observations began there in 1928. Flooding was reported along the Little Calumet River and Thorn Creek in the hardest hit areas. South suburban Lansing was drenched by 2.71" while Highland Indiana tallied 2.50" and Joliet recorded 2.47".
The rain fell in the midst of an October-level afternoon chill. Northeast winds gusted as high as 38 m.p.h. at Calumet Harbor and 35 m.p.h. at Gary while NOAA’s offshore buoy 30 miles east of Kenosha rode 5 ft. waves.
-Tom Skilling, WGN-TV Meteorologist
We've posted images of the damage inflicted by the thunderstorms that swept into Michigan City and the areas surrounding last Wednesday. What we've not posted are distant views of the storms responsible for that evening's severe weather—at least not until now! National Weather Service Cooperative Observer Roberta Slaby sends us these eyecatching photos of the towering cumulonimbus cloud responsible which spawned the damage in Michigan City. This view of the thunderhead is from 60 miles away in Bourbannais. (For those outside the Chicago area viewing these photos and not familiar with our local geography, Bourbannais is located 48 miles south of Chicago's Loop in Kankakee County). These photos were taken around 6:30 pm--about an hour after the first supercells rolled into Indiana off Lake Michigan. Roberta points to the "alpenglow" effect evident in these remarkable shots---that's the orangish glow often seen on snow covered mountaintops especially in winter as the sun sets. Radar scans at the time this photo was taken indicated cloud tops near 50,000 feet and cloud to ground lightning discharges approaching 690 with this storm complex and other thunderstorms within a 225 mile radius of Chicago.
-Tom Skilling, Chief Meteorologist, WGN-TV
PHOTO COURTESY: Roberta and Ed Slaby, NWS Cooperative Observer, Kankakee, Illinois
Days of mugginess are ending in Chicago as a drier northeast flow sets in for the better part of the week. Dew points plunged from near 70º early Sunday to around 60º by evening as the drying out process began. However, one more shot of showers will skirt the city Monday as a weather disturbance slips by to the south before several days of sunny and pleasant weather set in.
Storminess moved south with the humid air, bringing tornadoes, hail and torrential rain to parts of the southern Midwest. Several flash floods stranded motorists in portions of Missouri and southern portions of Illinois and Indiana Sunday. An inch and a half of rain in just 40 minutes closed roads in North Kansas City Sunday evening.
Meanwhile, Ernesto—temporarily weakened to a tropical storm after interaction with Haiti’s mountainous terrain—is expected to regain hurricane strength Monday as it crosses Cuba and takes aim at Florida.
--By Steve Kahn, WGN Weather Center Meteorologist
A sluggish front hung up across Chicago for several days has spawned repeat waves of potent showers and thunderstorms. While the city proper has escaped the bulk of the rain since last Thursday’s dousing, surrounding areas have not, with a trail of storm damage from northwest Illinois to northwest Indiana. All that should change by Tuesday as the front finally exits the region.
On Monday, rain should target downstate and brush the south suburbs. By Tuesday high pressure should depresses the rain south of the Ohio River, ensuring sunny, warm and less humid weather for the final days of August and meteorological summer 2006.
While Chicago’s weather improves with time, Gulf Coast residents are in a state of heightened alert as strengthening Tropical Storm Ernesto churns west through the Caribbean threatening to become a major hurricane in the Gulf of Mexico.
-Steve Kahn-WGN-TV Meteorologist
The week’s third wave of organized severe weather blasted areas northwest of Chicago Friday with thundery rains peppered by literally thousands of cloud-to-ground lightning strikes while bombarding areas in Boone and Winnebago counties with cascades of 1” diameter hail. The blinding downpours resulted as thunderstorms erupted repeatedly over four hours across a multicounty area of north-central Illinois. Deluges began around 2 p.m. near Rockford and continued nearly non-stop through 6 p.m. Two inches of rain hit the area around Illinois Highway 251 and the U.S. 20 bypass, while nearby Pecatonica recorded 1.15” of rain in just 15 minutes. But the heaviest rain appears to have hit near Belvidere where at least one unofficial report indicated 5.50” had fallen. A roof was blown off a house and a semi was overturned in Boone County; widespread flooding was reported there as well. High winds also downed trees and power lines in Genoa.
--By Tom Skilling, WGN-TV Chief Meteorologist
Garry England shares these photos with us of the widespread damage at Michigan City's Washington Park Zoo in the wake of Wednesday's 106 m.p.h. thunderstorm gust. Wind velocity data off the National Weather Service's powerful Romeoville-based radar at the time signaled a strong rotary circulation near that area, and the National Weather Service is asking anyone with photos or video of a tornado or funnels to contact Warning Coordination Meteorologist Jim Allsopp: jim.allsopp@noaa.gov
--By Tom Skilling, WGN-TV Chief Meteorologist
Severe weather troubles weren’t limited to the Chicago area Thursday. Nearly 24 twisters, some with multiple vortices (smaller twisters rotating within a larger vortex) skipped across the Dakotas and Minnesota with thunderstorms which bombarded the region with mammoth hailstones. The hail reached 4.25 inches in diameter—the size of grapefruit—at New Prague, Minn., and Selfridge, S.D. And in Stanton, N.D., the hail is reported to have destroyed vehicles and induced severe structural damage to some buildings. Northfield, Minn., was pounded for 20 minutes by hail which varied from golf ball to softball size. Crop damage was reportedly severe in the hardest hit areas. That’s not surprising: No form of weather has historically inflicted heavier damage to U.S. crops other than flooding.
Lake and Mc Henry counties in Illinois hosted the area’s heaviest rains Thursday. Hebron, Ill., where 0.80” had fallen in the preceding 32 days, was walloped by 2.40”.
--By Tom Skilling, WGN-TV Meteorologist
Storm described as the worst in memory by many in Michigan City, Indiana downs trees, powerlines; National Weather Service survey team suspects damage straightline wind induced
Chicago Tribune photographer John Smierciak shares these shots of Wednesday night's storm damage in Michigan City. John reports he took these photos at Washington Park next to the marina in Michigan City. A Great Lakes Environmental Research Laboratory wind sensor there recorded an extraordinary gust at the height of last night's storms of 106 mph. A trained spotter reported a tornado touchdown around 6:12 pm. However, the National Weather Service's Steve Eddy, Warning Coordination Meteorologist, and John Taylor, lead forecaster---both from the Northern Indiana NWS Forecast Office--have been on scene surveying the damage across northwest Indiana. Their observations and those of a helicopter overflight of the area suggest the trees knocked down are oriented in the same direction, a signature of straightline wind damage. A full report on the damage produced by that storm will be issued later today. Subsequent storms in the Chicago area produced 1.20" of rain at Midway Airport, reports the site's official NWS observer Frank Wachowski, bringing the South Side's August rainfall tally to 6.00"--the 9th heaviest since observations began there in 1928. Other storms across Wisconsin overnight have produced rain gauge measurements of 4"+ rain near Madison at Cottage Grove and Reedsburg in southern Wisconsin. There are Doppler rain estimates across the Badger State as high as 9-10" in areas over which t-storms have trained overnight and Thursday morning. Many thanks to former intern Chuck Heaver for his many reports from the scene in northwest Indiana last evening. Thanks, as always, to Jim Allsopp, our Chicago National Weather Service Warning Coordination Meteorologist for information on the ongoing storm survery there.
Tom Skilling, WGN-TV Chief Meteorologist
Gary Lawrence picks up wood from a roof that crashed into his antique shop from a closed factory in the backround while John Stelke looks at his van which was damaged by falling trees outside his home. Photos provided by John Smierciak
Damage on the lakefront in Washington Park next to the marina.
Viewer Robert Fesus of Round Lake captured these amazing photos this morning of the storm cells that rolled through.
Valaparaiso was among the northern Indiana communities swept by Wednesday evening's powerful thunderstorms. These photos, submitted to us by Gerry Jasinski, show quarter-size hailstones covering the ground at his home. Hailstones in other sections of northern Indiana reached diameters as large as 2.5"—large enough to be termed "tennis-ball size".
PHOTO COURTESY: Gerry Jasinski, Valparaiso, Indiana
Boats were snapped from moorings, a semi-trailer was flipped and at least two cars of a freight train in Michigan City were blown off the tracks as the area’s most powerful summer thunderstorms began roaring ashore Wednesday evening. Hail the size of tennis balls crashed to earth in the stormy downpours which were delivered by wind gusts so powerful as to be almost off the charts here. A Great Lakes Environmental Research Laboratory anemometer (wind sensor) near the harbor in Michigan City clocked a gust of 106 m.p.h. at about the time (6:12 p.m.) a trained observer reported a tornado touchdown in the city. Only the rarest of the planet’s estimated 50,000 daily thunderstorms produce triple digit wind speeds. The report of a touchdown was bolstered by the presence a Tornado Vortex Signature (TVS) on the National Weather Service’s powerful Doppler Radar—an indication of an especially strong rotation.
-Tom Skilling WGN-TV Meteorologist
Tuesday’s 87° high at both O’Hare and Midway was the city’s warmest temperature in the 18 days since the 89° high on Aug. 4. While only 7° above normal, only two Aug. 22 daytime highs have been any warmer here in the past 30 years. The 87° reading here was the same high recorded at Oklahoma City Tuesday. But there, the reading was significant because it marked the first time in 56 days readings failed to exceed 90°.
Cordoba, Alaska, on the state’s southern coast, has been swamped by 13” of rain in just the past two days. Like Chicago, August is southern Alaska’s wettest month. But the rains of the past two weeks have been extraordinary from the southeast Alaska Panhandle north to the Alaska Range. Normally the result of typhoon remnants, this year’s rains have been spawned by non-tropical systems and have buried glaciers above the 4,000 ft. level under snow.
-Tom Skilling
After this month’s blazing start with highs in the upper 90s and lows near 80º, August has taken on a much more temperate nature. Daytime highs have fluctuated between the upper 70s and upper 80s with overnight lows mostly in the 50s and 60s.
Despite the fact that the city has not experienced a 90º day in nearly three weeks, and Monday’s 55º low was the chilliest since July 7, August 2006—with a current average temperature running at 75.2º—still ranks as this city’s 27th warmest of the 136 on record since 1871.
Readings the rest of the week should cluster in the 80s, possibly reaching 90º on Friday.
An isolated shower may accompany Tuesday’s frontal passage, but the city’s best threat for additional rain is from late Wednesday into Saturday. Dew points will be on the rise during this period and the increased moisture levels will aid thunderstorm development as a series of fronts pass the area.
-Steve Kahn-WGNTV meteorologist
The southern tip of cool Canadian high pressure will be reinforced by a cold front Tuesday, begin to retreat north Wednesday, and reside north of the U.S.-Canada border by Thursday.
Temperatures will average only about 3 degrees above normal through Wednesday, but from that point on a significant increase in heat and humidity can be expected. The mean jet stream flow and storm track is forecast to shift north, allowing warmer and more moist air into the Midwest. Computer models suggest this pattern may persist the better part of a week with temperatures during that period averaging some 8 to 10 degrees above normal.
Humidity will be high with dew points in the upper 60s to lower 70s, and there will be an almost daily chance of showers or storms. As is the nature of convective storms, some parts of area will get more rain than others—but there is a good chance August’s almost 1-1/2 inch official rainfall deficit will be erased by month’s end.
--By Paul Dailey, WGN Weather Center Meteorologist
Persistent low-level cloudiness that covered Chicago yesterday and held over the area last night will thin out as it slowly drifts south and east this morning. The influence of high pressure centered over the western Great Lakes will finally result in abundant sunshine this afternoon. Visibilities will be unlimited along the lakefront, but gusty northeast winds could make near shore waters a little choppy. During the week ahead temperatures at O’Hare’s official observation site are forecast to reach at least 80° each day, allowing the string of 80s to reach 15 by next Saturday. Nearly an inch of rain fell at O’Hare (0.85 inch) late Friday and early Saturday, but the monthly precipitation is still over an inch below normal (totals are much above normal in southern sections). Showers and t-storms associated with a cold front Tuesday and then a warmer more humid unstable air mass later in the week could significantly cut this deficit.
-Paul Dailey, WGN-TV meteorologist
Saturday opens with muggy 70° dew points and relative humidities flirting with 100%—an indication the atmosphere is saturated with moisture. That moisture fueled overnight downpours and had reduced visibilities late Friday to an eighth of a mile at times near Waukegan. For areas adjacent to Lake Michigan, fog vulnerability is a major issue because air and water temperatures equal the dew point—and the dew point marks the temperature at which fog forms. With only limited wind Saturday, the prospect of sweeping clouds and haze from the sky with a push of dry air is low. That’s why it’s a good bet the first day of the Air and Water Show is to feature extensive haze, a good deal of cloudiness, and in some lakeside locations, the potential for fog.
Temperatures, as a result of all the moisture in the air, remained above 70° Friday for the 30th time this year at Midway—nearly twice the normal of 16 to date. Only seven years since 1928 have logged more 70°-plus overnight lows.
--By Tom Skilling, WGN-TV Meteorologist
More rain falls in August on average than in any other month of the year here. August’s 4.62” tally is nearly an inch higher than runner-up April’s 3.68”.
By this time of year, months of warm weather have allowed a huge volume of moisture to accumulate in the atmosphere over the U.S.—moisture which can be harnessed by thunderstorms that tend to move more slowly than their counterparts at other times of the year. This makes them especially prolific rain-producers. More 1”+ and 2”+ downpours have soaked Chicago in August than in any other month. The month is 3.5 times more likely to generate a 1”+ rain than February (the month with the fewest days of heavy precipitation historically) and 45 times more likely than February to host a 2”+ rain.
Interestingly, rainfall Friday will bring the number of days of measurable precipitation since records began in Chicago back in November, 1870 to 16,850.
-Tom Skilling
Cumulonimbus clouds produce the thunderstorms we experience on the ground. Larry Jahn of Macomb, IL photographed this cumulonimbus along a frontal system on a flight from Seattle to O'Hare around 4:30 pm Wednesday, August 2 while passing over Iowa. Ironically, it wasn't Larry's last encounter with this weather system. After a quiet arrival in Chicago shortly taking this picture, the same disturbance unleashed thunderstorms on Chicago "with a vengeance", Larry reports, canceling a connecting flight to Moline. Cumulonimbus clouds are the tallest on the planet and can reach altitudes of 70,000 ft. at times. The cloud pictured here appears to be about 30,000 ft. tall. Thanks for the photos, Larry!
-Tom Skilling
PHOTO COURTESY: Larry Jahn, Macomb, Illinois
The air heated by this Wyoming wildfire, captured by Tim and Sarah Sandman while driving toward their home in Buffalo, is behind the formation of the towering cumulus clouds evident at the top of the smoke plume. Heating encourages air to become buoyant and rise. Water vapor within the rising air cools with height, a process which leads to cloud formation as moisture condenses into droplets and becomes visible as a cloud. Thunderstorms have been known to develop above fires. Many thanks to Tim and Sarah for a chance to see wildfire-induced cloud formation through these photographs.
-Tom Skilling
PHOTO COURTESY: Tim and Sarah Sandman
South Siders, soaked on more than one occasion by August downpours, may find the dry weather gripping the city’s North Side this month hard to believe. But, rainfall at Midway Airport is running more than six times the amount which has fallen at O’Hare Field. The dry conditions extend to an impressive swath of the metro area north of I-88. Summer rain distribution is often a feast or famine affair. But, the variation since August 1 is truly eye-catching, ranging from 4.40" at Midway to just 0.72" at O’Hare. Only one year since 1990 has been drier at O’Hare—1999 with 0.67" to date. The disparity has only emerged in recent weeks. O’Hare’s 18.45" total since March 1 equals the 135 year average since 1871.
Rain has been in anything but short supply over the monsoon drenched Southwest. Tucson, Arizona’s 7.84" since June 15 makes it that area’s wettest monsoon season in over half a century—since 10.54” in 1955.
-Tom Skilling
