EXPLAINER: August 2006 Archives

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

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

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

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

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

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

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

For a month with a reputation of delivering its heat with lots of haze and humidity, Tuesday’s warm temperatures, low humidities and haze-free sunshine seem anomalies. Were it not for the wisps of high clouds predicted Tuesday afternoon off distant thunderstorms, the day would become only the 6th of meteorological summer (since June 1) to deliver the Chicago metro area 100% of its possible sun.
Quite a spread has developed between daytime and nighttime temperatures over the past 24 hours—a variation predicted to reoccur Tuesday and Tuesday night. With moisture levels as low as they are, the air takes on the character of a desert environment in the sense that it warms quickly by day then cools rapidly once the sun sets. With just 2 weeks left in the three month meteorological summer period, the season is running a modest 1.8° above the average since 1871 and ranks 33rd warmest of the past 135 years.
-Tom Skilling

A more tranquil weather regime is taking shape across the Chicago area this week as the atmosphere temporarily settles into a rather quiet and seasonable pattern. Extremes of heat or cold are not in the cards, and except for some thunderstorms early Monday and again late in the week, precipitation is not expected. Instead it appears that daytime temperatures will bounce about through the 80s.
Monday morning’s thunderstorms here will be the remnants of storm clusters that moved through the Mississippi Valley Sunday evening. Hail as large as golf balls pelted portions of southern Iowa and northern Missouri, while winds up to 70 m.p.h. downed trees and power lines; torrential downpours caused some street flooding.
Record heat was confined to south Florida Sunday with blistering highs of 99º at West Palm Beach and 96º at Miami, which followed a record-tying morning low of 81º there.
--By Steve Kahn, WGN Weather Center Meteorologist

Hot 90º weather is on hiatus as Chicagoans look ahead to a seasonably warm week with daily highs fluctuating within the 80s. Signs are subtle, but as daylight shortens, the atmosphere is slowly beginning to shift to a more fall-like pattern as meteorological summer winds down. Record heat was confined to Florida Saturday, while chilly morning lows established new records at Eugene, Ore. (43º), Hartford, Conn. (47º), Avoca, Penn. (48º) and Eureka, Cal. (47º).
Last week’s rains in the Chicago area targeted west and south sections while northern areas were left high and dry. Just the opposite was true 19 years ago when northwest portions were inundated by as much as 9.35” of rain in the Great O’Hare Flood of Aug. 13-14, 1987.
Rainfall chances this week appear limited to a Monday frontal passage and scattered activity late in the week as higher dew point air invades the region.
-Steve Kahn, WGN-TV Meteorologist

This weekend is to rank among the summer’s most beautiful and most comfortable since early June. Today is likely to be the first Saturday in which the “official” high fails to reach 80° since June 10. And, the coolest inland lows tonight in the metro area—i.e. the Fox Valley, DeKalb, Morris, Kankakee and Valparaiso—may end up not far from the record low of 51° set only two years ago in 2004.
Two days of northeast winds have sent the oppressively humid air responsible for Thursday’s thundery downpours packing. The atmosphere, from which 2.10” of water could have been squeezed earlier this week, holds a quarter that amount (0.50”) Saturday, a development obvious in the complete absence of haze. Interestingly, the driest air of all resides above 6,000 feet where relative humidities are predicted at a bone-dry 13% or less. Some of that dry air sinks to the surface and moves inland Saturday afternoon once daytime heating takes hold.
--By Tom Skilling, WGN-TV Meteorologist

The heaviest rain to hit the city’s South Side in four years began modestly Thursday in the midst of the evening rush hour. Sprinkles started falling across the area just after 5 p.m. But within two hours a full scale deluge was underway. Repetitive downpour-generating t-storms were to sweep southwestward over a narrow 20 mile wide corridor extending south from the Eisenhower Expressway westward into northern Will County. Strengthening NE winds appeared to provoke the rainy atmospheric set-up which unleashed 2.28" of rain on Midway Airport in just 78 minutes. A process known as “speed convergence” contributed to the area’s latest cloudburst. Strong NE winds off the low-friction environment of Lake Michigan converged once onshore with lighter winds slowed by friction produced by the land. Towering thunderstorms resulted halting the Sox game and flooding the Archer/63rd street intersection.

Residents of the Plains, scorched by blistering heat, would no doubt pay for the “cooler”, more comfortable air headed for Chicago in coming days. To characterize the weather ahead as “cool” is relative. The 70s predicted Friday and much of Saturday are actually seasonable—but a far cry from last week’s near 100°. Cool spells in August don’t mark the end of hot weather. Eight 90s typically occur from this point forward.
Oklahoma City hasn’t experienced a temperature below 90° since June 26. Fifteen of the past 16 days have exceeded 100°. New records were established Thursday at Joplin (102°) and Vichy/Rolla (100°) in Missouri and in Mississippi at Greenwood (102°) and Vicksburg (101°).
Downpour-generating rains flared at the periphery of the hot air. Lincoln was swamped by 1.77” Wednesday while a record-breaking 2.79” drenched Evansville, Indiana.
-Tom Skilling

Few here would have thought Tuesday’s official 78° Chicago high temperature was possible so soon after last week’s deadly intense heat. There’s been only one daytime reading in the past 28 days—a 77° high back on July 21—which has been lower. The cooler air arrived within a Canadian high pressure responsible for producing nighttime temperatures in the low 40s in northwest Wisconsin.
Careful observers here no doubt note the first subtle signs that summer is maturing and that autumn draws closer. Wednesday hosts 67 fewer minutes of daylight after six weeks during which days have grown shorter. Days, once 913 minutes in length as summer commenced on June 21, have shrunk to 846 minutes and the sun treks across Chicago skies 8% lower in the sky. This reduces the solar energy August sunlight delivers by 11% compared to June, the month with the most energetic sunlight.
-Tom Skilling

Only a week ago, brutally hot temperatures punished the area with a fifth consecutive day of 90° readings. Chicago was in the grip of the season’s most oppressive and ultimately deadly heat wave. This week’s weather couldn’t be more different.
Tuesday’s 84° predicted high on the heels of an 86° Monday promises the restoration of of late summer “thermal sanity”—which arrived amid thundery cloudbursts late this past Wednesday—intact.
Overall, Summer 2006 temperatures—those which have occurred since June 1—are firmly in surplus territory. Two-thirds of days have been warmer than normal and August is on its way to becoming the 14th of the past 15 months to post a temperature surplus.
News that Chicago is well into its latest “warm” month follows Monday’s announcement from NOAA that July finished 2nd warmest of any on record in the U.S. since 1895.
-Tom Skilling

Daily high temperatures will hold in the 80s and vary less than 10 degrees if forecasts pan out the next seven days. Overall readings look to average nearly 2 degrees above normal.
A cold front that moved slowly through the metro area Sunday gave mostly light showers on the order of a tenth to two-tenths of an inch of rainfall. Remnant cloud cover from that cold front will drift out of the area later tonight, leaving northern Illinois under the influence of high pressure Tuesday and Wednesday.
Computer models agree that a complex low pressure system will then move east out of the northern and central Plains, spreading clouds over northeast Illinois and providing several periods of showers and thunderstorms Thursday and Friday that could add up to over an inch of rain before precipitation ends early Saturday.
Next weekend may find Chicago under weak high pressure with significant low pressure systems to the east and west.
--By Paul Dailey, WGN Weather Center Meteorologist

Ahead of a cold front approaching from the northwest, a warm southwesterly flow will pull moist unstable air into Illinois today. Saturday saw a couple tornadoes and numerous reports of large hail in North Dakota and Minnesota ahead of the front, and severe storms could redevelop over northeast Illinois this afternoon and early evening. The front is expected to slowly move through and just south of the area overnight with remnant clouds and showers possibly hovering over southern portions tomorrow. Tuesday and Wednesday will see the area under the influence of high pressure. Then a complex low pressure system is forecast to move east out of the northern and central plains. This will result in extensive cloud cover along with showers and thunderstorms here the remainder of the week. Tropical Storm Chris made landfall in eastern Cuba Saturday, and has become just a weak low pressure system.
-Paul Dailey, WGN-TV Meteorologist

It’s hard to imagine only days after bidding one of the hottest air masses here in 11 years adieu that Summer 2006 could possibly be averaging cooler than a year ago. But, it’s true. Temperatures since June 1 are running 2.2 degrees behind last year. And, while the set of 90°-plus highs predicted Saturday and Sunday are to produce the Chicago area’s third warmest weekend of the 10 since the season began, the city’s official tally of fifteen 90s lags behind last year’s 19 to date.
Friday’s 28 percent late-day relative humidity underscored the dramatic decline in atmospheric moisture of the past two days. The once oppressive tropical rain forest-like 76° dew point midweek had yielded to dry 48° dew point air. To the eye, the area’s haze-shrouded midweek horizons were sharply defined Friday. Humidities went into an afternoon free-fall as air heated by strong August sunshine ascended, tugging cooler air off Lake Michigan and encouraging dry air aloft to sink to the ground.
--By Tom Skilling, WGN-TV Meteorologist

The hum of air conditioners, dominant here for more than a week, faded dramatically Thursday afternoon with the arrival of an air mass bearing 44% the moisture of its humid predecessor and responsible for temperatures which “felt” 24-degrees cooler. Chicago’s Friday morning 60s are the area’s coolest readings of the past 10 days. The 2"+ deluge (2.03" at Midway Airport) responsible for the weather shift which lambasted the area Wednesday night into early Thursday, qualifies as the city’s heaviest 24 hour rain tally on the South Side since November 18, 2003.
Plunging temps aren’t limited to the Midwest. A mammoth 1,500 mile swath of the U.S., involving all or parts of 20 states, is in on the stunning weather change. The eastward-charging cool air will extinguish record highs like Thursday’s 101° at Washington, D.C., 100° at Central Park in New York City and 100° at Baltimore, Maryland.
-Tom Skilling

Chicago enters a sixth day of 90s Wednesday and the third consecutive day of brutal heat and humidity. It’s part of a dome of heat which first entered the national spotlight weeks ago as a wildfire-producer in the West, then grew even more ominous as temperatures within it surged ever-higher and heat related deaths began to mount. By late Tuesday, sections of 29 states were in its grip.
Chicago logged a rare second official 99° high Tuesday—a reading 16° above normal and only a degree shy of the day’s record. Sets of readings at such oppressive levels have occurred here only 13 of the past 135 years.
The last 6 days has produced the most oppressive heat here since the deadly 1995 episode, and constitutes the second warmest late July/early August period on record since 1871.
Area heat indexes Tuesday soared to 120° at Gary and 117° at Northerly Island.
-Tom Skilling-WGN-TV Meteorologist