The coolest late June air mass in decades spills over into Wednesday, but it is to loosen its grip on the area later this week in time for the 4th of July holiday weekend. The abnormally cool 65-degree high predicted Wednesday would deliver the Chicago area its coolest July opening in 79-years--since a 65-degree reading in 1930. A temperature at that level at this point in the season is more typical of early May and 18 degrees below normal for the date. It comes on the heels of the coolest June close in 23 years. Clouds and northwest winds were so pervasive that highs struggled to reach 66 at O'Hare International Airport. Northern Wisconsin and Upper Michigan highs failed to make it out the 50s. Rockford's 65 degree high Tuesday broke a record for the coolest June 30.
Cloudiest June in 4 decades
June 2009, which ended at midnight, closed as the Chicago area's cloudiest in the four decades since 1969, having only 51 percent of its possible sunshine. A typical June sees 68 percent.
A mass of cool air more typical of May than late June is in firm control of Chicago's weather and appears to have the area headed for one the coolest July openings in 79 years. While temperatures struggle to a high of 70 Tuesday, the predicted 67-degree high Wednesday would make it the city's coolest July 1 since a 65-degree reading in 1930.
The temperature pullback is in dramatic contrast to last week's heat and humidity, which featured a string of three 94-degree highs. The cool pool of air is of Canadian origin, with a faster than normal vertical temperature decline. Such air masses are said to be "unstable" because milder air remains buoyant as it ascends into the chilly air aloft. It's a process that may produce widely scattered light showers Tuesday and Wednesday.
Quiet to the north
Not a single report of severe weather occurred in May and June across northeast Wisconsin north into Upper Michigan. It's the first time that's happened since severe weather records started there 30 years ago.
Much drier and cooler air follows the thunderstorm-producing cold
front that passed through
Chicago overnight. Severe thunderstorm
warnings were issued for counties west of the metro
area with a 70
m.p.h gust reported in Franklin Grove, Lee County and 60+ m.p.h. gusts
reported at Ottawa, Mendota, and Earlville in LaSalle County. A strong
low pressure center is
forecast to develop and intensify over the
eastern Great Lakes early this week with the
resulting northwest flow
pulling much colder air into the western Great lakes and Midwest.
Clouds associated with the low will spread out far to the west,
covering most of northern
Illinois as well as a good portion of
Wisconsin, Michigan and Indiana. Showers, perhaps even
a few
thunderstorms are possible both Monday and Tuesday under this
unseasonable setup
which should see high temperatures some 10 to 15
degrees below normal.
Warmer, closer-to-normal readings later in the week
As the low pressure system slowly moves northeast, clouds will break
and temperatures are
expected to slowly modify later in the workweek.
Friday's break in the three-day string of 94-degree highs Chicago area residents sweltered through Tuesday, Wednesday and Thursday, ends briefly Saturday afternoon and evening when a resurgence of heat is expected to result in the week's fourth 90-degree-plus high--and set the stage for potentially powerful thunderstorms expected to hit with a cold front Saturday night.
Friday's official 86-degree high at O'Hare International Airport occurred at 11:29 a.m. before readings declined slowly through the afternoon as northeast winds delivered cooler air.
Perhaps even more significant was Friday's humidity pullback. Dew points--a measure of atmospheric moisture--dropped 15 degrees from the low 70s Thursday to the mid-50s late Friday.
Changes ahead
Big weather changes loom--including the threat of potentially severe storms Saturday night--as
temperatures fall to the low to mid-80s Sunday then the low to mid-70s Monday and Tuesday.
The first break in the heat and humidity of the past three days rides into the city on northeast winds Friday.
The air's moisture content retreats from levels more typical of the Gulf of Mexico to those more more closely identified with the Midwest's North Woods region.
Thursday's 94-degree high was the third in as many days, making the three-day spell Chicago's hottest in nearly three years.Only two other occasions since temperature readings have been taken at O'Hare International Airport have highs as warm or warmer than those observed the past three days occurred this early in the summer.
State of the lake
Lake temperatures have warmed to 2009's warmest levels. Satellite estimates of Lake Michigan's average surface temperature now stand at 68 degrees. And the U.S. Army Corps of Engineers reported Thursday that lake water levels are 10 inches higher than a year ago.
Thursday evening threat fizzles under "nose" of powerful jet stream
Heat and humidity as high as Thursday's typically facilitate thunderstorm formation. But area residents caught a break Thursday. Thunderstorms to the city's north and west--including one with 62 m.p.h. gusts at Whitewater, Wisconsin, dissipated as they moved in Chicago's direction, once they encountered storm-extinguishing sinking air beneath the nose of a pocket of
powerful jet stream winds.
Thunderstorms exploded to life along a narrow 20 mile wide corridor from Cook County southeastward into northwest Indiana midday Wednesday. An inland-moving lake breeze front was the meteorological culprit. It ushered easterly winds off Lake Michigan into a hot, humid air mass dripping with 1.50 inches of evaporated water. The inland racing flow encountered a windless tropical air mass, producing a pile-up of air which was forced to rise and cool. Thunderstorms soon resulted and towered above 50,000 feet unleashing torrential downpours. As much as 2.12 inches was measured at the Weather Bug rain gauge at Frazier Magnet School in Chicago as 63 m.p.h. winds raked Midway Airport and floodwaters submerged streets and basements in Cicero. The storms erupted over the same corridor repeatedly between 1 and 3 p.m.---a process referred to as "training." They generated more than 1,700 cloud to ground lightning strokes in just over two hours.
Heat enters third day Thursday; more storms due
Three consecutive 90-degrees have occurred at this early stage of the summer season in only one of three years at Midway Airport since 1928.
The mercury reached 90 degrees in Chicago for the first time in 2009 at 12:09 p.m. Tuesday on its way to the warmest June high temperature in the city in four years.
The 94-degree high at O'Hare International Airport equaled last summer's hottest temperature.
This year the heat is late to arrive in Chicago. Since 1928 at Midway Airport, an average of five highs of 90 degrees or warmer have occurred by this date.
Heat fuels Iowa storms
Near triple-digit heat in Iowa fueled powerful thunderstorms with cloud tops that towered to 57,000 feet and sent temperatures diving more than 20 degrees while producing 60 m.p.h. wind gusts and numerous reports of large hail.
The storm cluster began Monday evening in Colorado and is the latest in a series to rotate around the periphery of a dome of hot air in what meteorologists refer to as a "ring of fire" pattern.
The same hot air mass responsible for 89-degree highs Monday-the warmest
temperatures to date in 2009 at O'Hare International and Midway Airports
tightens its grip on the Chicago area Tuesday and Wednesday. Heat
advisories have been hoisted for all but lakeside areas where light
onshore (easterly) afternoon winds should temper highs to the 80s while
90s occur inland. Wednesday may prove to be the hottest of all with heat
indexes approaching a dangerous 106 right up to the lake.
Monday's heat and humidity in southwestern Iowa reached extreme levels
when the country's highest dew point, 82 degrees, combined with a high
of 93 degrees to produce a 117-degree heat index at Shenandoah, Iowa.
Florida heat
After several days of suffocating heat and humidity, Florida is in line
for somewhat cooler weather Tuesday. More temperature records tumbled
Monday with Vero Beach leading the heat parade with a record high of 102
degrees and a heat index of 111.
As if taking a cue from the calendar, Chicago's weather has finally turned summery and will remain so through the week. It won't be oppressively hot or oppressively humid.
And thunderstorms--an integral component of the warm season around here--will be in and out of the picture through Friday, but the great majority of hours during the five days will be dry.
Chicago sits at the northern edge of hot air to the south, and that air mass will repeatedly splash into the city this week, then retreat slightly.
Southern heat is on
Sweltering summer temperatures and sticky humidity are no strangers to the southern half of the United States in June, July and August. Residents there accept it and deal with it. This year, though, oppressive heat and humidity arrived early and hit hard from Kansas,
Oklahoma and Texas east across the Deep South. Many cities there have been establishing daily high temperature records since early last week, and computer models indicate no significant change to the sultry pattern this week.
Saturday's sunshine gave residents across northern metropolitan Chicago a chance to recover from the flooding rains and damaging winds that swept through the area Friday afternoon. Commonwealth Edison expects power to be fully restored today to all of the 120,000 households that lost electric service. Having dealt with periods of swollen rivers, impassible roads and flooded basements literally since September, 2008, waterlogged Chicagoans are increasingly voicing sentiments like, "Enough, already!" Nothing would please them more than a couple weeks of sunny, rain-free days.
The "Ring of Fire"
Unfortunately, an extended period of dry weather is not in the picture. A massive "dome" of very warm, humid air sprawling across the south half of the nation is expected to remain in place for several days. Chicago sits in a turbulent boundary zone at the northern periphery of that heat dome -- within a meteorological "ring of fire" that is a fertile breeding ground for thunderstorms.
The atmospheric ingredients for severe thunderstorms --warmth, high humidity, an approaching cold front, a 45-m.p.h. low-level (5,000 feet) jet stream and a vigorous disturbance at higher levels---are falling into place Friday. It's a situation that favors the development of thunderstorms with large hail and damaging outflow winds this afternoon and evening. Heavy rainfall and flash flooding are additional concerns, especially considering
our soggy soils.
Summer arrives, big time
Until now, the temperatures that Chicagoans associate with summer have been sporadic and short-lived. By this time next week, however, summer heat and humidity will have arrived in Chicago, and computer models suggest it will be more than a one- or two-day tease. Rather, the onset of a new and warmer weather regime across the Midwest suggests, for Chicago, a multi-day string of afternoon temperatures near or above 90 degrees, accompanied by uncomfortably high humidity. The timing is appropriate: Summer (astronomical summer) begins on June 21.
A dramatic weather pattern shift (for which the Midwest is notorious) is beginning to unfold. The change from a cool, cloudy and rainy weather regime to sunny, hot and humid conditions gets under way Thursday, though it will be a multi-day transition. The Storm Prediction Center advises that a powerful impulse moving across portions of the central and southeastern United States is likely to trigger severe thunderstorms here (and elsewhere in a band from Minnesota to the Carolinas) later today. Storms move out of the Chicago area by Saturday morning and the weekend looks dry.
Warm, muggy days ahead
A broad swath of the nation from Oklahoma and Texas east to Georgia has been sweating through 90-degree temperatures and oppressive humidity for several days. That air mass is expanding northward and is due to arrive in Chicago in about a week. And once it gets here, the muggy weather is likely to persist for several days. Beginning one week from today, computer models indicate a string of five to seven days here with afternoon temperatures in the 90s.
A few showers may linger into this morning following Tuesday's thunderstorms that unleashed street-flooding rains over far southwest suburban Chicago, and another round of thunderstorms is likely late today into Friday. It's a story that we're getting used to hearing: Those storms could bring locally heavy rain. Looking ahead, an abrupt change signals at least a few 90-degree days by month's end.
Where are the mosquitoes?
It's a question that we're beginning to hear, prompted by the frequent and heavy rains that we have been enduring this spring. Dave Zazra of the North Shore Mosquito Abatement District says culex mosquitoes (the carriers of West Nile virus) breed in standing water, but our frequent rains have prevented stagnant pools from forming. "If all of a sudden we stopped getting these flushing rainstorms, that could be a problem," he said. Mosquito abatement officials caution that, due to the uncertainty of the weather, it is too early to predict the nature of this mosquito season.
Warm temperatures have been notable in their absence so far this season, a
fact not lost on the area's warm-weather devotees. History tells us that an
average spring delivers about 16 days (Midway Airport data) on which the
high temperature reaches at least 80 degrees by this date, and three days at
or above 90 degrees. Thus far, Midway has logged only nine 80-degree days
and no days in the 90s. That's about to change. Heat and humidity that has
been resident across the south third of the nation for several days is
expanding northward and arrives here in strength later this week.
Kansas battered
Warm, humid and unstable air that extended from the southern Great Plains
east to the Appalachians proved to be a fertile breeding ground for severe
weather in all its manifestations. A tornado near Dodge City, Kansas, was on
the ground for ten minutes late Monday afternoon and another twister struck
near El Dorado. Hail 2.75 inches in diameter bombarded Alta Vista, Kansas,
Monday evening, shattering windows and damaging roofs.
Enjoy today's sunny sky and pleasant temperatures. Those conditions won't last because Chicago's weather pattern is set to be stormy by mid-week.
Two distinct weather systems will be surging across the Midwest in upcoming days. The first arrives with showers and thunderstorms late Tuesday and continues into early Thursday.
Total rain accumulations could exceed 1.5 inches. A second system arrives late Thursday and brings another round of showers and thunderstorms from late Thursday through Friday into Saturday.
The impact of a cold lake
Away from the shore, Lake Michigan water temperatures are now running from 48 degrees to 54 degrees. That's why air blowing off the lake is so chilly at this time of the year. On sunny days with east winds, lake-cooled air warms as it moves inland, typically moderating 10 to 15 degrees by the time it arrives at the Fox Valley. On cloudy days, the moderation is less than
5 degrees.
After a June that opened with record chill following a spring characterized by clouds, sub-normal temperatures and deluges of rain, Chicagoans increasingly anxious for summery warmth, sunshine and rain-free days must face another meteorological disappointment. A consensus of computer models suggests that below-average temperatures are likely to persist here through the week. In addition, persistent east winds blowing more often than not off the chilly waters of Lake Michigan will keep lakeshore areas especially cool in upcoming days. A good deal of sunshine today and Monday is just a tease. Another storm system is headed toward Chicago and the Midwest.
The bad news
In a weather situation more reminiscent of January than June, computer models indicate the development of a "closed upper low" over the Midwest. This feature is a large and slow-moving pool of chilly air 15-30 thousand feet aloft, beneath which the weather is mainly cloudy, showery and cool. That system arrives here Tuesday and persists into Saturday.
The cloudy, chilly and rainy open to June here has been the talk of the town. So far this June is running more than 12 degrees cooler than last year, and the clouds, rain and chilly lake winds have been persistent. The average temperature at O'Hare International Airport through Friday has been only 59.5 degrees: nearly 7 degrees below normal and the coldest since records there began 50 years ago.
More bad weather is on the way Saturday with a cold rain expected to linger through the bulk of the morning. Rainfall could be heavy -- especially north of the city, which would be a reversal of Thursday's deluge that targeted the southern suburbs.
Better days ahead
Encouraging signs in recent computer runs signal a change to more typical June weather which by now should feature daily highs around 80 degrees. A return of sunshine should boost temperatures well into the 70s Sunday and Monday, though lake cooling will continue. By midweek a northward shift in the jet stream promises a steady diet of highs in the 80s, though showers and thunderstorms are likely to accompany the warm-up.
Enjoy today's dry interlude -- it won't last long: The next storm system is quickly heading this way. Area rivers, swollen with runoff from heavy rains across southern metropolitan Chicago on Thursday, won't have much time to drain before a new round of thunderstorms rolls in Friday night. Rain continues through much of Saturday, but Sunday looks dry. Temperatures continue on the cool side through the weekend and persistent winds off Lake Michigan will keep it especially cool in lakeshore areas.
Looking ahead, a major weather pattern shift is in the works and it signals summery warmth -- finally -- but its effects won't arrive here until the middle of next week. Temperatures well into the 80s are likely by next Wednesday, accompanied, unfortunately, by humidity that also carries an ongoing threat of thunderstorms.
Thursday's deluge
Thursday's rain was a study in contrasts. Little or no rain fell across the north half of the metropolitan area (only 0.01 inch at O'Hare, for example) and residents there probably wondered what the fuss was about, but torrents of rain struck southern sections and northwest Indiana. Kankakee County in Illinois and Lake and Porter Counties in Indiana were especially hard hit by flash flooding. The rain finally ended late Thursday afternoon.
We're anxious for some sun and warmth, especially after we've put a moderately harsh winter behind us, but it's not to be. Wednesday's sun was uplifting, but temperatures -- held down by northeast winds off Lake Michigan -- remained in the 60s across much of the city area. Southern sections, less affected by lake cooling, warmed into the 70s. Chicago's
official high of 67 degrees was nine degrees lower than usually chilly Anchorage, Alaska, which basked in 76-degree air. But things get worse today. Another storm system sweeps from the Great Plains across Illinois, and Chicago finds itself with clouds and rain, and even cooler temperatures.
Severe weather Wednesday afternoon
Severe thunderstorms rumbled across a huge area of the Great Plains Wednesday afternoon and evening. As of 9 p.m., the Storm Prediction Center had logged 12 tornadoes in seven states: Wyoming, Colorado, Nebraska, Kansas, Missouri, Oklahoma and Texas. A thunderstorm complex produced straight-line winds of 70-90 m.p.h. across large portions of the Dallas/Fort Worth area.
Tuesday's 67 degree high made it the coolest June 9 in 11 years, a reading more typical of early May and 11 degrees below normal.
Temperatures through the opening nine days of June are running 11.5 degrees below the same period a year ago, ranking June's opening among the 20 coolest here in 139 years of weather records. Myriad factors drive weather patterns, but it appears the persistence of wet weather through spring--it was the wettest spring on record at Midway Airport--on the heels of the wettest year on record in 2008 has produced a huge swath of wet soil across the Midwest. Wet soil inhibits warming by contributing to increased cloud cover and rain. Chicagoans have seen only 40 percent of the area's possible sunshine--well below the 68 percent considered normal.
Twisters and hail
Thunderstorms slammed sections of Kansas and Missouri producing seven twisters, more than 3 inches of rain and bombarding some locations with windshield-shattering hail. Sleeper, Mo., was hit with 2.75-inch diameter hail.
Monday's thunderstorms hit in several waves. Downpours in pre-dawn
storms totaled more than 2 inches (heaviest at DeKalb, 2.20 inches and
Dixon 2.05 inches), prompting flood warnings in the west and northwest
suburbs.
Afternoon storms hit hardest in northern counties and
areas of southern Wisconsin. The strongest storms developed in
southeast Wisconsin towering to heights of 45,000 feet. Ping-Pong-ball
size hail struck near Mukwonago and high winds toppled trees. Several
funnel clouds were sighted in the area. Blinding downpours also
accompanied the Wisconsin storms, with nearly an inch of rain flooding
streets in the Janesville area.
The storms formed on the heels
of the area's most humid air mass since last September. Dew points, a
measure of atmospheric moisture approached 70, readings typical along
the Gulf coast.
Cooler weather will dominate the rest of the
week, with another round of rain and thunderstorms on Wednesday. Warmer
weather will return by the weekend, with highs returning to around 80
degrees.
As June enters its second week, Chicago continues to experience cool
weather. Few area residents have even considered turning on the air
conditioning so far this season and some still have had their furnaces
running on recent cool mornings. Heat and humidity have remained bottled
up across the Southern states while a preponderance of north and
northeast winds have kept the city quite chilly. Except for a brief
intrusion of warmth and humidity Monday, little change in the cool
pattern is expected in the week ahead.
Showers and thunderstorms are expected to traverse the area today and
Monday. With temperatures in the 80s just south of Chicago colliding
with chilly 40s and 50s to the north, strong storms are possible with
the potential for some heavy rainfall through Monday evening. So far this spring there has been little severe weather in the Chicago area. While frequent rains have targeted the area, the lack of true warmth and 70 degree Gulf-level dew points have kept severe weather espisodes to a minimum.
Record late-season snow hits North Dakota
The latest-in-the season measurable snow on record whitened portions of western North Dakota Saturday as two to three inches of snow fell near Dickinson. Several record lows were set across the upper Midwest Saturday including 27 at International Falls, 31 at Rhinelander, Wis., and 32 at Marquette,
Mich.
Friday's bright sunshine, aided by gusty west winds that overwhelmed any attempt by the cool air hovering over the lake to surge ashore, produced the city's warmest temperature readings of June. Temperatures peaked at 80 degrees at Midway Airport for only the sixth time this year-equal to the number of 80-degree days by this date a year ago, but only half the 12 considered average.
Alaska has had more warm weather this June than the Chicago area. Fairbanks has recorded highs of 70 degrees or higher every day so far this month while Chicago has only been able to muster two.
Frost advisories for the North Woods
Temperatures will drop into the 30s Saturday morning across portions of the upper Midwest from northern Minnesota to far northern Wisconsin and Upper Michigan, where rare June frost and freeze advisories were issued. Another chilly night is expected Saturday night with lows near 40 degrees.
It hasn't been as warm as Friday's predicted 76 degrees in nearly a week.
The
break in this week's chilly weather is welcome after one of the seven
coolest June 1-4 periods here in the last half century. But, the warmth
wanes Friday night and Saturday with a cold front passage and wind
shift to the northeast. And the potential for downpour-generating
thunderstorms for least a portion of Sunday calls into question just
how much warm air may return to the area that day.
Weekend
rains won't be continuous. But when precipitation does occur, it may
arrive within clusters of thunderstorms capable of downpours,
especially Sunday. By the time the developing wet pattern exits
Tuesday, 2 or more inches of rain may have fallen here.
Storms erupt in record Pacific Northwest heat
Seattle
baked at 91 degrees Thursday--a record. Heat in the region produced
uncharacteristic severe thunderstorms, with 70 m.p.h. gusts and 0.71
inches of rain in 20 minutes near Harrisburg, Ore. Fairbanks, Alaska,
hit 83 degrees.
Chicagoans can bid farewell to the area's coolest early-June weather in
eight years Thursday. Not since 2001 has a June opened here with
back-to-back readings as cool as Tuesday's 60 degrees and Wednesday's 61
degrees. Wednesday's high made it one of the six coolest June 3 since
1928.
Unlimited sunshine is to boost Thursday afternoon readings by 7 degrees
with far more modest northeast winds likely to limit the reach of lake
cooling to areas within a mile or two of the lake. Southwest winds
Friday are predicted to send temperatures into the mid-70s-warmth likely
to spread to the lakefront.
80-degree days ahead
Though warm temperatures have been in short supply of late, warm weather
enthusiasts should take heart. Weather records reveal a near 100 percent
chance that the coming month will bring five or more 80 degree or higher
temperatures. The first may occur as early as Sunday if thunderstorms
don't impede the northward movement of a warm front.
It's the third day of meteorological summer-but it certainly doesn't
feel that way. Wednesday's predicted low 60s would be right at home in
mid-April. Highs as chilly as Tuesday's 60 degrees at O'Hare
International Airport and 61 at Midway Airport have occurred this late
in the season only 29 of the past 81 years (or, on average, about a
third of the time).
Though it's far too early to write off summer heat, many Chicagoans
sense warm seasons haven't been as hot as they once were. It's a
proposition we investigated-and there's more than a shred of truth to
it. While Chicago's overall June-through-August average temperatures
have risen slowly the past five decades (from 72.5 degrees in the 1960s
to 73.9 degrees in the 1990s), the number of truly hot 90+-degree days
has waned. Since 2000, the annual average of 18.3 days at or above 90
degrees at Midway is down from 23.2 days in the 1980s and 21.1 days in
the 1990s. Summer days have cooled an average of 0.46 degrees since the
1990s while summer nights have warmed 1.64 degrees during the same
period.
The weather of two seasons visited Chicago on Monday, setting the stage for downpour-generating thunderstorms that prompted a late-day weather watch.
Waves of thunderstorms towering 44,000 feet into the atmosphere unleashed local rains of 1 to 2 inches and flooding was reported in areas near Rockford and Belvidere, where 4 to 6 inches of water covered some roads late Monday.
Meantime, severe thunderstorms hit east central Illinois, producing a reported tornado touchdown near Hoopeston.
The wet pattern that dominated the just-completed meteorological spring is to continue. The past two weeks have seen 2.23 inches of rain fall at O'Hare--almost a half inch more than normal for the period. A suite of computer models suggest about the same amount of rain the next two weeks.
As the weather system moves off to the east, showers will gradually diminish Wednesday morning. Cooler drier air will feed into northeast Illinois and persist the remainder of the workweek.
The next chance for significant rains occurs on the weekend.
