July closed with eye-catching temperature deficits over a wide swath of the northern U.S. overnight. Chicago's 69.4-degree average July temperature at O'Hare International Airport was the coolest of the past 17 years. But at Midway Airport, the month's 71.0-degree average temperature was the site's coolest in 42 years. Estimates based on the month's temperatures suggest the need for air conditioning was 30 percent below the long-term average.
Cool as it's been in Chicago, in a number of Midwest cities July has never been cooler. Records were established in Rockford; Madison, Wis.; South Bend and Ft. Wayne, Ind.; and Benton Harbor, Saginaw and Flint, Mich. The month's temperature in those cities finished 4.5 to more than 7 degrees below normal.
The month's lack of rainfall was impressive -- and a huge change from the wet spring that kept farmers out of their fields. Only 1.53 inches of rain was measured here in July, less than half the 3.51 inches considered normal. The dry weather has led to browning lawns.
Thursday afternoon's atmospheric setup was hardly one to produce a major severe-weather outbreak. But a bit of sun peeked through the day's clouds allowing temperatures to rise and winds did vary in speed and direction with height---a situation which caught the eye of forecasters at the Storm Prediction Center. They issued a late-day advisory cautioning that thunderstorms under development across sections of northern Illinois and southern Wisconsin might become capable of producing a few weak funnels. When Doppler radar scans of air movement within an eastbound cluster of thunderstorms over Boone County exhibited strong rotation, a tornado warning was issued around 4:20 p.m. for eastern Boone into McHenry Counties. Within moments of the appearance of circulation on radar, trained ground-based storm observers spotted a funnel cloud above far northwest suburban Capron. It soon extended to the surface where it produced 72 m.p.h. wind gusts that tossed dirt and tree debris into the air. Gusts strengthened to 83 m.p.h. by 4:30 p.m. as the parent thunderstorm, with cloud tops extending to 31,000 feet, continued east into McHenry County at nearly 30 m.p.h. The twister remained small and weak and went on to produce no damage before dissipating.
Pacific Northwest Temperatures
Cool breezes developed in some coastal areas of the Pacific Northwest, lowering temperatures late Thursday. But another record occurred in Seattle (95-degrees) and blazing heat is predicted to continue in interior sections of Oregon and Washington into the weekend.
July 2009 closes as Chicago's coolest in 118 years
The month closes at midnight Friday night and appears likely to finish as Chicago's coolest July in 118 years.The average temperature of 69.4-degrees over the first 30 days is more than 4-degrees below the long term average. It becomes the first July in 139 years of records here which has failed to produce a temperature greater than 86 degrees. An 86 degree high occurred earlier this month on July 6--a reading never exceeded.
As July winds down, the brutal heat responsible for a swarm of record high temperatures across the Pacific Northwest and triple-digit readings in many sections of the West and Southwest is showing no sign of making a move on Chicago. Temperatures here will remain comfortable, with readings near or a bit below typical mid- and late-summer levels. While July's average temperature in Chicago ranks 3rd coolest of the past 81 years--running nearly 4-degrees below normal--Rockford and South Bend and Ft. Wayne, Ind., are all on track to close the books on the coolest July on record. The breadth of the month's cooler-than-normal weather has been, and continues to be, remarkable, literally covering the entire Midwest. Some weather observation stations are reporting July temperature deficits approaching 8 degrees.
Wednesday's 81-degree high in Chicago marked only the 34th time this year the temperature has reached 80 degrees. Records reveal a typical year has logged 49 such days by now--44 percent more than this year's tally.
Tuesday proved one of July's warmer, more humid days. Midway Airport's 86-degree high equaled the month's warmest reading while O'Hare's 84 degrees fell two degrees short. A line of thunderstorms bubbled to life during the afternoon and evening across the southern suburbs from Streator to Michigan City and La Porte, Ind., emanating from clouds which towered to 50,000 feet. The storms hit a 10-mile-wide corridor paralleling Indiana's Lake Michigan shoreline from Porter into La Porte Counties especially hard over a nearly three-hour period, unleashing repetitive downpours which began around 5:30 p.m., and ultimately led to nearly 5 inches of rain at Indiana Dunes State Park. Burdick, Ind. -- just east of Chesterton -- was drenched by 2.78" while 1.30" was reported in nearby Portage in just over 75 minutes.
Blistering heat in the Western U.S. included record-breaking triple-digit readings at a number of unlikely locations across the Pacific Northwest including 106-degrees at Vancouver, Wash. -- the hottest not only for July 28 but a new all-time high there -- and 106 degrees in Portland, a record-breaker for the date and just one degree shy of its all-time high.
"Wake low" produces damaging pre-dawn winds in west/northwest suburbs
Powerful pre-dawn winds gusting as high as 55 to 60 m.p.h. downed trees and snapped limbs over a swath of the Chicago area Monday night and Tuesday morning extending from west suburban Huntley in the far northwest suburbs west of Algonquin east to Roselle and Waukegan. Dissipating thunderstorms were behind the powerful gusts -- the product of what meteorologists refer to as a "wake low". The winds occur when a region of low pressure develops north of dissipating thunderstorms, strengthening the outflow winds which flow from them. The strongest gusts occurred between 11 p.m. and 1 a.m.
The cooler than normal July temperatures which have slashed air conditioner bills across much of the Midwest and East Coast appear all but certain to establish a new temperature benchmark by the time the month ends at midnight Friday. With the reading of 86 degrees set back on the 6th likely to stand as the month's warmest since July 1, the month is likely to become the first July in 139 years of official records here which fails to produce a temperature of 87 degrees or warmer. Monday's 84-degree high -- far from an exceptionally warm reading -- was the city's warmest in 12 days.
Several clusters of thunderstorms are likely to sweep the Chicago area Tuesday. Half inch diameter hail accompanied storms in Ogle County Monday evening just northwest of Polo.
Severe storms produce tornado touchdown south of La Crosse, Wis.
Thunderstorms have erupted five of the past seven days somewhere in the mid and upper Midwest. Monday's storms produced a tornado touchdown 37 miles south/southeast of La Crosse, Wis., around 5:18 p.m. Law enforcement officials indicated the twister generated numerous reports of damage there. Storm downpours across southwest Wisconsin -- from the towering 50,000-foot-tall thunderheads responsible for that twister -- were impressive and included 1.62" at Friendship, 1.58" at Muscoda, 1.50" at Mineral Point and 1.46" at Fennimore.
Thunderstorms pounded southern Minnesota, portions of Wisconsin, eastern Iowa and northern Illinois Friday afternoon and evening with hail, high winds and driving downpours -- and were expanding into sections of the Chicago area late Friday evening. Doppler radar scans detected tornadic circulations, prompting tornado warnings north of Dubuque in sections of eastern Iowa and south of Platteville in southwest Wisconsin.
Trained spotters in Dubuque reported rapid rotation within a funnel cloud which hovered above the city around 6:30 p.m. Gusts of 65 m.p.h. hit the city a short time later -- while 70 m.p.h. winds and torrential downpours combined to knock out power to the National Weather Service Office in Davenport while flooding downtown streets there. Rockford was hit with 60 m.p.h. winds around 9:10 p.m. Reports of heavy rain were widespread: In just 45 minutes, 2.75" swamped Aurora, Iowa, while 1.10" of rain fell in 15 minutes in Freeport.
The storms, which produced nearly 11,000 cloud-to-ground lightning strokes from eastern Iowa into northwest Illinois in just 6 hours, were produced by thunderstorms towering as high as 54,000 feet where temperatures plummeted to 69 degrees below zero. Little wonder the storms were prolific hail producers. Hailstones the size of tennis balls -- 2.50" in diameter -- lambasted an area 2 miles northwest of Oneida in Iowa's Delaware County. The day's largest hailstones, measuring 4.25" in diameter (grapefruit size) pounded Winneshiek, Iowa. And hail was responsible for severe crop damage along U.S. Route 20 just west of Dubuque.
Storms headed this way---but Friday has a shot at becoming July's warmest first
An impressive thunderstorm outbreak looms Friday night. The potential for severe weather will have to be monitored. But it's Friday's warm-up which is front and center as the day dawns.Never in the 81 years of weather observations at Midway Airport have Chicagoans found themselves 24 days into the month of July without a reading above 86-degrees on the books. Never, that is, until this summer. But with daytime heating and the healthy assist of strengthening southwest winds, Friday temperatures have a respectable shot at surging past that reading and reaching 88-degrees. The extent of cloudiness filtering the day's sunlight will play an important role in determining just how daytime temperatures go. An 88-degree high would be the city's warmest in the four weeks since June 27 when an 89-degree reading occurred.
Thunderstorms exploded to life in Thursday's unstable atmosphere and doused the evening rush hour over sections of the metro area. Wauconda was hit with 1.67 inches of rain in 20 minutes. Other totals included 1.48 inches at Resurrection High School's Weather Bug rain gauge in Chicago, 1.35 at Harwood Heights where 40 m.p.h. thunderstorms gusts delivered the rain, and 1.26 at Des Plaines and Forest Park. The downpours were selective. No rain was recorded at O'Hare.
The evolving pattern the next 2 weeks is looking wet; regular t-storms could bring 2 to 5-inch totals.
Daytime heating ignited scattered but vigorous thunderstorm development over Chicago's northwest suburbs Wednesday afternoon. The slow moving storms unleashed localized downpours--including the 1.24 inches which drenched west suburban Huntley--at the same time triggering the funnel clouds reported at 1:50 p.m. over Woodstock in McHenry County and around 3:50 p.m. near Ogle County's Rochelle. The funnels--a product of strong thunderstorm updrafts brought on by the fast rate at which temperatures dropped with height Wednesday---also produced small hail, much of it nickel sized. Radar scans at several points during the afternoon indicated the storm's towering parent clouds reached heights of up to 42,000 ft.
In southern Wisconsin's Elkhorn, situated in Walworth County, a thunderstorm cluster stalled producing a deluge which spanned several hours---peaking between 3 and 3:45 p.m. Serious flooding was the result.
Easterly winds off Lake Michigan cooled the air just enough in lakeside counties of northeast Illinois and northwest Indiana Wednesday--that storms were unable to develop.
While haze, low clouds and areas of fog greet area residents as Thursday gets underway, clouds are predicted to break allowing some sunshine to emerge. This should re-heat the still unstable atmosphere, setting the stage for a repeat of the scattered thunderstorm development which drenched part of the area Wednesday.
Chicago's official high temperature Tuesday topped out at 80 degrees--only the ninth time readings have reached 80 or higher this month--as driving downpours drenched sections of northwest Illinois and eastern Iowa, with some areas reporting 3 inches or more of rain. Hardest hit was the area surrounding Dubuque and Galena. Totals included 3.10 inches at Asbury and Maquoketa, both in Iowa, and 2.24 inches in Dubuque. The totals equaled a full July's rainfall at many locations and began just after daybreak. Downpours increased, becoming heavy by late morning and through much of the afternoon. The big rains set up in moist, highly unstable air beneath diverging branches of stronger than usual late July jet stream.
The Chicago area is not alone in stunning lack of summer 90s.
Cooler than normal weather has been the rule this summer not only in Chicago, but in much of the eastern half of the nation. While Chicago has logged only about a third of its normal 90s to date, Boston and New York have both recorded 25 percent or less.
The cool summer has impacted Great Lakes water temperatures. Each lake
is running 5 to 9 degrees below levels observed at this time a year
ago. Chicago's water temperature near Navy Pier is 5 degrees off last
year's 74-degree reading.
Chicago isn't alone with cooler than normal July temperatures. Monthly temperature deficits--a number of them quite impressive--are on the books for July at every major Midwest reporting station. A nationwide analysis of July temperatures from NOAA's Climate Prediction Center indicates nearly half the Lower 48--from the northern Rockies across the Midwest and up and down a wide section of the East Coast--have experienced sub-par temperatures. While Chicago's July 1-20 average temperature is running 5.4-degrees below the area's 138 year average, other July deficits include 6.5-degrees at Marquette, Mich., 6.1-degrees at Cincinnati, 5.7-degrees at Grand Rapid, Mich. and 3.7-degrees at Des Moines, Iowa.
The cool air has had consequences. In its weekly update on U.S. crops, the USDA reported only 26 percent of Illinois' corn crop has reached the pollination stage--the lowest level at this point in a season in 12 years. At the same time, estimates of air conditioning usage based on temperatures to date suggest levels 58 percent off the normal for July and 31 percent off typical summer levels.
Area residents have seen the second fewest 80 degree or higher July temperatures in 81 years---only nine of them! Weather records reveal it's hard to turn the tide on cool patterns once they've dominated this much of the summer season. Of 13 years with comparably cool temperatures through July 21, only 3--just 23 percent---have managed warmer than normal August temperatures.
Unseasonably cool weather continued to grip the Midwest and upper South Sunday, with highs failing to reach 80 degrees as far south as Tennessee. Nashville recorded a record low high of 77 degrees, while Louisville did the same with a high of just 73. Readings fell into the 30s in northern Minnesota Sunday morning, with Embarrass registering a frosty 33 while International Falls logged a record-breaking 37. Since Friday, the highest temperature Chicago could muster was 72 -- great for mid-May, but rather chilly for mid-July.
In stark contrast, intense heat is baking the Southwest. Death Valley recorded its ninth straight day of 120-degree-plus temperatures Sunday with a high of 126. That California desert site hosts the nation's all-time record high of 134 established on July 10, 1913. Record highs also tumbled in Texas, with Corpus Christi at 98, Brownsville at 100 and McAllen at 106.
Readings will gradually warm into the 80s this week in Chicago, but the below-normal temperature trend is expected to continue and 90s aren't due anytime soon. Scattered showers and storms also will affect the city this week, with the most widespread and heaviest activity expected late week.
July begins climb to regain summer status
So far, July 2009 has been a cool one with temperatures averaging well below normal. Though no 90 degree days appear to be in the immediate picture, there is growing confidence that readings will return to normal midsummer levels in the middle 80s this week. Though Sunday's mid-70s high will be warmer than Saturday's 72-degree reading, high temperatures will still be nearly 10 degrees below typical mid-July levels. Under clearing skies and a light wind regime, lows Sunday night are expected to dip into the middle 50s threatening Monday's record low of 53 degrees established in 1970.
As the week progresses, the center of the cool air will slide slowly east and southerly winds will bring an increase in both warmth and humidity. Early in the week precipitation will be limited to scattered hit-or-miss afternoon and evening thunderstorms. A more significant system is expected by week's end bringing with it a threat of more widespread thunderstorm activity.
What a summer! Many Chicago area residents are just shaking their heads -- some pleased by the lack of heat, others disappointed at the failure of hot weather to gain a foothold here. Extremely rare mid-summer lake-effect rains were pouring down on sections of La Porte and Berrien Counties in Indiana and Michigan Friday evening -- just the latest meteorological twist in a summer of topsy-turvy weather across the region.
July has slipped to the coolest to date here in 42 years -- its 68.7 degree average temperature running nearly 5 degrees behind the long-term (138-year) average. Friday's 70-degree high was the first time in 53 years a July 17 temperature failed to rise above 70 -- you'd have to travel back to a 64-degree high 85 years ago to find a July 17 that was cooler. In Rockford, Friday's 67-degree high broke the record for the date, becoming the coolest July 17 high on the books. The reading was Rockford's fourth record-low daytime maximum to fall since June 30.
July's average Chicago highs rank among the two lowest in 50 years at O'Hare
The average high for July's first 17 days has been 77.5 degrees -- the second coolest in the 50 years of O'Hare Airport weather records dating back to 1959. Only 1967's 76.2-degree tally has been cooler.
It's not often a set of mid-to-late July days produce temperatures which fail to break above 70-degrees. Yet that's what's predicted for the Chicago area Friday and Saturday. A mass of unseasonably cool air, which only days ago was 1,100 miles north of Chicago over Canada's chilly Hudson Bay, is riding well developed northwest winds associated with a buckling North American jet stream into the city. It's a development likely to deliver a good deal of instability cloudiness and passing light showers in addition to highs of 68-degrees Friday and 70-degrees Saturday--the city's coolest mid-to-late July two-day spell in 28 years. On only three other occasions over the 81 years in which temperatures have been recorded at Midway Airport have back-to-back days at this point in a summer failed to break above 70-degrees.
Thunderstorms erupted over sections of the Chicago area late Thursday. Radar scans put maximum cloud tops at 36,000 ft. Winds gusted to 60 m.p.h. as the storms swept across south suburban Crete Thursday evening. Earlier, 55 m.p.h. had been clocked west of the city in Glen Ellyn and 38 m.p.h. winds raked Midway Airport. Small hail accompanied some of the storms and downpour just at Plainfield totaled 1.17 inches in just 22 minutes right before 7 p.m. Valparaiso, Indiana was doused with 0.88 inches of rain in 20 minutes.
A buckling jet stream is behind the cool-off here and heat plagued Oklahoma and north Texas, where a powerful storm hit Thursday lowering Oklahoma City's temperature from the day's high of 99-degree to 82-degree by nightfall. Coming days will see the country's hot air shift west into the Rockies and Southwest while May level temps take over across into the weekend in the Northeast U.S.
The cool summer of 2009 is poised to deliver another round of below normal, May-level daytime readings Friday and Saturday.
Thursday's predicted 82-degree high may be the last 80-degree reading likely to occur in the Chicago area until Tuesday. With extensive cloudiness expected to accompany the abnormally cool incoming air mass, readings will be hard-pressed to break above 70 degrees. Temperatures at such levels this time of the year are truly rare--81 years of weather observations at Midway Airport show only six instances in which back-to-back highs in late July have been as cool as the 68-degree and 70-degree highs predicted for Friday and Saturday. A buckling jet stream is behind the predicted cool-down. Northwest winds stacked vertically from the ground tens of thousands of feet aloft assure the flood of cool air from Canada will be hard to stop.
Widespread cloudiness and the fact that Midwest days are nine hours shorter than those in the Arctic this time of year are among the factors helping southbound air masses to grow cooler as they sink into our area.
Thunderstorms--some potentially strong and capable of generating wind-driven downpours and hail--greet at least some residents of the Chicago area as Wednesday dawns. Atmospheric moisture levels have surged to Gulf Coast levels just west of the area overnight. Up to 1.84 inches of evaporated moisture is available for thunderstorms to tap. An expeditious retreat of these storms is predicted by mid morning, clearing the way for emerging sunshine and the most humid surge of air this month. Dew points, a measure of atmospheric moisture, are to rise above 70-degrees for first time in two weeks--levels comparable to those found on the Gulf Coast. At the same time, sunshine is to send temperatures to within striking distance of 90-degrees. And, despite predictions of May level temperatures with an impressive late week and early weekend cool-off here, weather records reveal hot temperatures aren't history just yet. In 81 years of observations at Midway Airport, only one year---1967--- has failed to produce at least one 90-degree high beyond July 15.
Flooding rains drenched sections of Minnesota Wednesday. Pillager, Minn.--not far from Duluth---was swamped by 6.30 inches of thundery rainfall. Near Brainerd in the northern section of the state, 5-inch rains were common---much of it falling in just 2 to 3 hours.
Tuesday's sunshine and comfortable temperatures and humidities belie the severe weather threat predicted to come together after midnight and into the predawn hours Wednesday. That's when strong fast-moving thunderstorms are to sweep across the Chicago area from the west, possibly delivering downpours, hail and potentially strong winds. The vigorous, jet stream-borne disturbance expected to ignite these storms was behind an eruption of severe weather Monday afternoon across the northern Plains and was still in progress as night fell. Several storms generated cloud tops scanned by radar to have heights of 67,000 feet. The worst of these storms unleashed grapefruit to softball-size hail that broke windows in buildings and cars at Hulett, Wyo. Another bombarded St. Francis, S.D., with hailstones the size of baseballs. At least five reports of twisters were filed with the Storm Prediction Center across four states, from Montana to the Dakotas, a region covered by five severe weather watches-two for tornadoes and three for thunderstorms.
This summer's days have generated much larger temperature deficits than the nights
Chicago is in the midst of its coolest July open in 40 years. The month's average temperature through late Monday was 68.5-degrees---four degrees below the long-term (50-year) average at O'Hare International Airport. The month has produced fewer than half the 80-degree or higher temperatures during the same period a year ago. The cool readings have had a beneficial effect. It's estimated these lower temperatures may have reduced the need for air conditioning by more than half.
While the southern half of the country continues to bake, cooler Canadian-source high pressure looks to dominate Chicago and northeast Illinois weather during
the week ahead.
The weather pattern along the Gulf Coast states and the southwestern U.S. is expected to change very little, so daily highs in the 90s over the Southeast and the lower 100s over the Southwest should persist.
But across the northern tier states, including Illinois and Indiana, average highs are forecast to remain at or slightly below mid-July normals.
Cool summer in city
Chicago's average temperature from June 1 through July 10 has been 67.5 degrees. This is the coolest since 1992, which followed the eruption of Mt. Pinatubo in 1991 north of Manila. That eruption spread a layer of dust aloft around the world that cut back on the amount of solar radiation. This year's average summer-to-date temperature is 2.1 degrees cooler than the normal of 69.6 degrees and only 0.9 degrees above the 66.6 recorded in 1992.
This year's average temperature as of July 10 was 2.1 degrees cooler than the normal of 69.6 degrees and only 0.9 degrees above the 66.6 recorded in 1992.
July's opening days have hit Chicagoans with a double meteorological whammy: subpar temperatures and far less sun than normal. The area has seen only 35 percent of its possible sunshine from July 1 to 10. Not since 1969 has the period hosted so little sunlight. A typical July sees 68 percent of its possible sunshine.
Saturday morning's clouds and scattered showers give way to sunshine and declining humidities by afternoon. A pre-dawn cold frontal passage is allowing drier Canadian air to move slowly into the area -- an air mass that will dominate the weekend and produce warm midsummer temperatures.
But while seasonable readings are predicted here, a fourth consecutive day of brutal heat is to blaze across the central and southern Plains. In Oklahoma, Friday thermometer readings topped out at 112 degrees at Gage and 111 degrees at Enid, Medicine Lodge and Clinton. Warnings for excessive heat cover sections of states from Arizona to Texas, Louisiana, Oklahoma and Arkansas.
Severe thunderstorms threaten to rake sections of the Chicago area Friday. The warmest temperatures here in two weeks this afternoon are to heat an atmosphere dripping with 2 inches of evaporated moisture, initiating the process of thunderstorm formation. Air rises and cools when that happens, especially when temperatures decline with height at a faster-than-usual rate. The atmosphere is labeled unstable by meteorologists in this situation. Add an unusually energetic jet stream with winds diverging overhead and the stage is set for atmospheric fireworks. That same roster of conditions late Thursday generated 52,000-foot-tall thunderstorms that bombarded north-central Iowa with golf-ball-size hail and wind-driven downpours. Weather watches may become necessary in the Chicago area later Friday and Friday night as the volatile situation unfolds.
Where are the 80s?
Thursday's official Chicago high fell just short of 80 degrees--hitting 79. There have only been 20 days with readings 80 degrees or warmer at O'Hare International Airport (31 is average). It's the lowest tally of 80-degree-or-higher days here in 35 years--since 1974 when July 10 arrived with only 19 days of 80s on the books.
East winds off Lake Michigan had temperatures on a downward trajectory Tuesday afternoon. Instead of warming, readings slipped nine degrees at O'Hare International Airport over 5 hours---falling slowly from 77 degrees at noon to 68 by 5 p.m. An incoming overcast and a few sprinkles combined with the air flow off the cool lake water, which still hovers in the 60s, reversed the typical surge in temperatures that occurs through mid and late afternoon. The resulting May-level temperatures spill into a second day Wednesday with lakeshore readings unlikely to escape the 60s because of extensive cloudiness expected to limit any warming sun. Cool winds off the lake have a stabilizing effect on the atmosphere, slowing the upward motion of air that might otherwise produce a few thunderstorms. This will deflect the day's southeastbound thunderstorms well west and south of Chicago, leaving sprinkles that could build to a few showers. The dominance of cooler than normal temperatures has produced Chicago's coolest July in 25 years.
Wildfires in Alaska
Visibilities from Prince William Sound into Alaska's interior have been limited in recent days as smoke from 64 active wildfires burning in the state settled over the region. In the state's Interior, Fairbanks---where temperatures reached the 80s Tuesday---reported visibilities slashed to just 5 and six miles. McGrath, Alaska recorded an 88-degree high.
July is off to cool start, averaging more than 5 degrees below normal. The month's first six days have come in at just 67.3 degrees, well short of the 50 year average of 71.6 at O'Hare International Airport. This makes the opening six days of July 2009 one of the eight coolest July openings since weather observations began on the Northwest Side in 1959. Monday's high of 86 degrees and the 81-degree high on Sunday provided quite a contrast to July's cool trend. Monday was the warmest day of the month to date.
But 80s aren't likely to be repeated Tuesday. The re-emergence of northeast winds off Lake Michigan brought on by Canadian high ridges southward into the Chicago area, pressure will slash Tuesday afternoon's highs by at least 12 degrees even as blistering heat expands into the Plains. The developing clash in coming days between the two widely varied air masses will promote the formation of thunderstorm clusters--expected to initially track to the west and south of Chicago, brushing the area with several showers Tuesday and Wednesday. But by Thursday, the growing dome of heat threatens to nudge storms farther north, potentially affecting Chicago.
Latest stats confirm summer among the coolest/wettest on the books here
The three month meteorological summer period, which gets underway June 1, has averaged 67.5-degrees--more than degree below normal and ranks among the coolest third of all summers on the books here since 1871. The 7.43 inches of rain nearly twice the 4.34 long term average and places the period since June 1 among the wettest 9% on the books.
A sunny and warm Sunday afternoon turned showery late as rains developed along a wind-shift line moving southeast out of Wisconsin. Though the showers were low-topped and produced little thunder and lightning, they did spawn numerous funnel clouds west of the city along a corridor between Interstate Highway 39 and the Fox Valley. These funnels were "cold air-type funnels," the kind not associated with severe thunderstorms that almost always dissipate without producing any damage.
After a chilly 4th of July, temperatures rebounded into the comfortably warm lower 80s Sunday, a level expected to repeat here through midweek. Hot weather has been noticeably absent from the city since a streak of 90s in late June, but the latest suite of computer forecasts hints at a brief surge of hot weather that should reach the city by Friday. The downside to the expected warm-up will be a threat of showers and thunderstorms that will continue to add to the city's growing 2009 precipitation total that has now reached 26 inches -- nearly three-quarters of the city's normal annual total of 36.27 inches.
Chicago's 4th of July weather was a bummer: cool and rainy. The official high of 69 degrees at O'Hare marked the first time since 1997 (66 degrees) that the holiday failed to break 70, and the 0.20 inches of rain was the most since 1.72 inches fell in 1995. The only positive note was that most of the rain ended during the early evening, a few hours before scheduled holiday fireworks. Warmer weather is on the horizon as a persistent dome of hot air that has been baking the central and southern Plains and lower Mississippi Valley with record-breaking heat appears to be making a move toward the area. Triple-digit heat shattered 4th of July temperature records in Texas Saturday, led by a 107-degree high at McAllen. Chicago-area temperatures are expected to surge into the 90s by Thursday and again on Friday for the first time in two weeks. Gulf-level dew points in the 70s will accompany the heat, assuring that recently silent air conditioners will be humming again. The heat will also bring another round of thunderstorms -- adding to area rain totals that are nearly 9 inches above normal for the year.
Eastbound low pressure, which first developed late Thursday with an eruption of thunderstorms across the western Plains, is behind Saturday's gray, cool weather so reminiscent of much of this area's spring and early summer. Blazingly hot air charged with a huge supply of tropical moisture is fueling Saturday's cloud and shower-producer here. But, its heaviest downpours are to drench Missouri, Downstate Illinois and Indiana with thundery deluges that may deposit local rains of 4 inches or more. More conservative totals appear a good bet in the Chicago area. An average of 30 widely varied computer rainfall estimates suggests precipitation here may average 0.61 inches -- though individual projections range from as little as 0.02 inches to as much as 2.61 inches. Summer rains are fickle and often widely varied, which supports the huge spread in projected rain totals. With clouds expected to limit temperatures to levels more than 10 degrees below normal and winds off the lake likely to limit shoreline highs to the 60s, Saturday may end up the area's coolest in 12 years.
Friday afternoon's predicted 80-degree temperatures over much of the metro area will mark the first time this week it's truly felt like summer. Many Chicagoans have openly voiced disappointment over the recent succession of lackluster daytime highs which have been more reminiscent of May than late June and early July. But increased sunshine Friday is to allow temperatures to surge. It's a move that finally returns temperatures here to seasonable levels.
Storm clouds loom Friday night into Saturday over sections of the Midwest. Thunderstorms that flared late Thursday over the Plains (with cloud heights towering as high as 57,000 feet and prompting a series of severe weather watches) are targeting sections of Iowa, Missouri, Downstate Illinois and Indiana.
A suite of computer projections has shifted these storms progressively farther north in recent days. Individual projections of potential Chicago rainfall late Friday night into Saturday varies widely across 15 models. The average of these forecasts calls for a total of 0.52 inches. A consensus of these forecasts places the axis of potentially heaviest rainfall across central Illinois and Indiana.
Much improved weather is due Sunday with sunshine allowing temperatures to surge back into the 80s in all immediate Lake Michigan shoreline locations where upper 70s are likely. Evidence that hot weather is preparing to stage a comeback later next week continues to mount. A dome of hot air is predicted to become established over the nation's mid-section by Thursday---a development which may well produce the Chicago area's next round of 90-degree temperatures. The heat could lead to increased rainfall. Rainfall estimates in the 1-2 week range here passed two inches in several computer projections, evidence a sporadically stormy "ring of fire" pattern could take shape, sending a succession of thunderstorm clusters running along the northern flank of the predicted dome of hot air across the Chicago area with some regularity.
What has happened to summer? That was the question from many area residents Wednesday amid May-level 60-degree temperatures. The day's high of 65-degrees marked the chilliest open to a July here since 1930 and was one of the three coolest July 1 readings on the books in 139 years of weather records since 1871. Summer temperatures at that level are truly rare. Of 7,452 meteorological summer (June through August) highs on the books since 1928 at Midway, only 184 of them--just 2 percent---have registered temperature as cool or cooler.
Scattered lake-enhanced rain showers amid the Wednesday's chill lowered cloud bases in the downtown area, obscuring the tops of skyscrapers while producing periods of upper 50-degree temperatures.
While Chicago missed the July 1 record low maximum of 61-degrees set 1904 and 1924, record low daytime highs occurred at Rockford (65-degrees) and downstate at Lincoln where the high was just 70-degrees.
Thundery downpours could be part of the holiday weekend downstate
Thunderstorms expected to erupt in the Plains later Friday threaten to track east/southeastward into sections of downstate Illinois and Indiana where they may produce downpours totaling 2 or more inches for a portion of the upcoming July 4 holiday weekend.
