WGN Weather Center Blog

The agricultural community, always weather conscious, is well aware that moisture deficits across Illinois are becoming critical, but, for most of us oblivious to the consequences of meteorological abnormalities, dry weather usually means sunny, pleasant days and a dry commute.
With a precipitation total of 5.00 inches for March 1-May 31, spring of 2005 takes its place in Chicago weather history as the seventh driest in 135 years of precipitation records. The long-term average for that period is 9.39 inches, and Chicago’s departure from average, 4.39 inches, has prompted the United States Department of Agriculture to designate the area’s soil moisture deficit as “incipient drought.” That’s the first stage in a five-step tier of increasingly harsh soil moisture deficits that extends from incipient to moderate, severe, extreme and finally exceptional drought.

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Today’s bright sunshine, low humidity, reasonable wind speeds and moderate temperatures define a perfect day, and they come on the final day of the season that meteorologists and climatologists refer to as “meteorological spring”—March, April and May.
May has been on the cool side locally and across much of the central and eastern United States, and in Chicago fully two-thirds of its days registered below-normal temperatures.
Tomorrow, of course, marks the beginning of meteorological summer, so chosen because at most locations in the Northern Hemisphere it consists of the year’s three warmest months: June, July and August.
Appropriately enough, the advent of summer this year coincides with the onset of a warming trend that will ultimately deliver the season’s highest temperatures to date. It won’t be a heat wave by any means, but readings in the middle and upper 80s this weekend will be summery.

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Today’s expected high temperature near 70º should be the coolest of the week, because a multiday period of rising temperatures begins tomorrow. The culmination of the warming—Saturday’s anticipated high of 88º—should it come to pass, will be Chicago’s warmest temperature in 294 days (that’s four-fifths of a year!) since the city registered 90º last Aug. 3.
A realignment of upper-level winds (above 10,000 feet) is triggering the warming—not just here but across the two-thirds of the nation east of the Rockies. Computer models tell us that persistent northwesterly upper-flow, instrumental in recent days in directing cool Canadian air to the Midwest, is about to give way to a multiday period of upper-level southwesterlies.
Six consecutive days of warming, while noteworthy, challenges no records. From April 22 through May 2, 1901, Chicago logged an 11-day spell of rising temperatures that carried daily highs from 40º (April 22) to 87º (May 2).

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Chicagoans anxious for a return of summer’s heat will have to keep waiting. The consensus of computer models is that a major weather pattern change is in the works, and though it will take several days for the entire realignment to occur, its implications for Chicago are significant. Area temperatures that have been running near or below seasonal normals in recent days will be heading into the surplus category by next weekend.
It will be warmer—readings into the 80s—but it certainly won’t be a heat wave.
For most of us, 90º is the definition of a hot day. Midway Airport logs 24 of them in an average year, the first one typically arriving on May 29. With no 90s yet in sight, this year’s first occurrence will be delayed.
Midway’s temperature climatology suggests patience in that regard. Every summer has delivered 90° temperatures, but in 1928 the season’s first 90° day did not arrive until July 2.

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Seattle on Friday was under a Heat Advisory with highs in the lower 90s expected—some 20 degrees higher than normal. At the same time, northern Illinois experienced readings 20 degrees cooler. It will take the first half of the week ahead, but the cold upper-level low that has dominated Great Lakes weather will slowly drift east, allowing a ridge of high pressure to build out of the southwest into the Midwest. The resulting southwest flow will push 80° readings into northern Illinois by next Thursday with the first 90s of 2005 possible next weekend. However, the immediate interest is in this Memorial Day weekend with latest indications of a significant rainfall Sunday night as low pressure tracks just to south and east of Chicago. Memorial Day may start off with rain, but as the low moves east, clouds should thin as sun breaks through in the afternoon.

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Inland locations of California, Oregon, and Washington experienced highs well into the 80s and 90s Thursday; meanwhile, New England shivered in the 40s and lower 50s with freezing rain and wet snow observed in the mountains of Maine and New Hampshire. Chicagoans located in between, ended up with readings in the lower 70s, about half-way between the two extremes. Today could see more of the same although skies over northeast Illinois will start out sunny but quickly see popcorn-like cumulus clouds develop during the forenoon with scattered showers even thunderstorms during the afternoon. Cold air aloft and heating at the surface will create very unstable atmospheric conditions over northern Illinois today. By early next week the upper low should be well to east, still dominating New England weather, while Illinois appears to be establishing a slow warming trend culminating in 80° temps Thursday.

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Temperatures take off Thursday, reaching the highest levels here since Sunday’s 80°. Chicago sits beneath the nose (leading edge) of powerful 110 m.p.h. jet stream winds. Air sinks on a vast scale there, drying and compressing in the process. Skies clear when that happens and temperatures soar. The meteorologoical situation is stunningly similar to this past Sunday, which began cloudy and turned gloriously sunny and windy. Though moisture is limited, an isolated gusty t-storm could flare in several spots late today.
Florida broiled in record heat while New Englanders shivered through record daytime temps Wednesday. Ft. Lauderdale’s 92° and the 93° in Miami contrasted with Boston’s 46° afternoon reading—a mid-March level temp.
A brief tornado touchdown at Port Saint Lucie, Florida around 3:15 p.m. Wednesday afternoon moved a police patrol car 100 feet and uprooted a large tree.

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It comes as quite a surprise for many U.S. residents east of the Rockies, especially after an unusually mild winter. But, with the exception of intermountain West and the southern Plains, most of the eastern U.S. has entered the final days of a very cool May. By the time the month ends next Tuesday, a number of Eastern cities will close the books on one of the coolest May’s on record. In Boston, where gale force winds accompanied March level 40° temps Tuesday, the month is running 5.8° below normal and likely to become the city’s 3rd coolest since records started in 1872. Philadelphia is running a 3.7° deficit for the month. Baltimore is headed for the conclusion of its 2nd coolest May since 1870 while the Nation’s Capitol may post its 8th coolest May—also since 1870. Chicago’s May temp deficit (-1°) is surprisingly modest given the cool days which have so often dominated.
-Tom Skilling

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Northeast winds sent temps here tumbling as they took hold around 3 p.m. Monday. They’ll continue to blow off Lake Michigan Tuesday for a 15th day this month. It’s a stat which means the city has been cooled by lake winds 60% of the time in May, 2005. Little wonder so many become frustrated by the slow pace at which warming takes place here each warm season. The flow returns May to its cool ways, limiting shoreline highs to the 50s—though readings warm to 67° at some inland locations Tuesday.
The cool temps here contrast with the record-breaking triple-digit heat, which has blazed for a week to Chicago’s west—and with March-level 40s predicted in New England Tuesday amid the powerful 40+ m.p.h. coastal winds of an unusual late season Nor’easter. Gusts at Nantucket and on Martha’s Vineyard are to reach 50-60 m.p.h. at times later Tuesday.
-Tom Skilling

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The good news is that Chicago area temperatures soared as high as the lower 80s Sunday as morning cloudiness and a few passing sprinkles gave way to brilliant afternoon sunshine. The bad news is that Sunday’s highs will likely not be approached again this week. Cooler air will be filtering into the area in the week ahead as jet stream winds turn northwesterly, sending air of Canadian and arctic origin into the area. Most days should see highs in the 60s and lower 70s right into the Memorial Day weekend.
Hot air is making an early season statement in areas from the southern Plains to the desert Southwest. Temperature records tumbled Sunday from Louisiana to southern California. The Dallas area recorded its second consecutive 99º record high while blistering triple-digit heat set records in the Southwest, including Needles (114°) and Palm Springs (112°) in California, and Tucson (109°) and Yuma (110°) in Arizona.

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A cluster of t-storms is expected to roll through the city this morning with a second batch possible during a period of afternoon heating. With cold air aloft along with a strong NW jet stream, some storms could bring hail and strong winds similar to the storms that struck this area late last Thursday.
Chicago’s high officially made it into the lower 70s Saturday, but lakeshore areas could not get out of the 60s courtesy of this spring’s seemingly persistent northeast winds. Max temperatures in the upcoming week should be capped in the 70s on the warmest days, and on Monday readings may struggle to even reach the lower 60s.
In contrast, the season’s first wave of 100° temps continues to expand in the Desert Southwest, while early season temperature records tumbled from Louisiana to Colorado as readings there soared into the 90s. Dallas-Forth Worth established a new record high Saturday topping out at 99º while the 98º high at Oklahoma City also rewrote the record books.

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Sweaters and light jackets were back in style in Friday’s northeast winds. The flow limited Northerly Island on Chicago’s lakefront to 57°. But, peak readings the next two days surge 17° above last weekend’s levels.
Blistering Plains heat produced tornado-bearing t-storms late Friday in North Dakota. At least five twisters were reported from mammoth t-storms which towered nine miles above the region’s rolling landscape. While the heat remains locked in place to Chicago’s west this weekend, the t-storms may not. Patches of clouds off these storms blow into the metro area and mix with the day’s sun Saturday. Thundery weather could reach some sections late Saturday night. But, the atmosphere threatens to produce a fast-moving breed of t-storm beneath powerful jet stream winds Sunday. Such storms are notoriously high wind producers.
-Tom Skilling

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The heavens opened Thursday —not once, but twice! The first thundery wave of rainfall swept the area before sunrise. Then, brief midday sunshine produced warming and ignited a new round of storms in the afternoon. Downpours, within which cloud-to-ground lightning flashed at a rate of 600 times every 10 minutes within a 200 mile radius of Chicago, produced larger rain totals than any storm since last summer and included hailstones which ranged from nickel to baseball size. By day’s end, 1.26” had fallen at O’Hare. The last time more rain fell there was the 1.41” total recorded last Aug. 28. Totals were impressive at other locations as well, including 1.34” at Romeoville, 1.39” at DuPage County Airport and 0.72” at Midway Airport.
The storms, which reached heights of 42,000 ft., produced 25 reports of large hail across the metro area and 145 reports of severe weather in sections of 10 states Thursday.

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Powerful t-storms had unleashed ten twisters in Iowa and Minnesota by late Wednesday. Three of the ten were in Minnesota, where debris was reported by two law enforcement officials on Highway 29 near Benson in the west-central section of the state. Farther south, a tornado was on the ground at least 10 minutes in western Iowa near Fort Dodge.
A large spring storm is encouraging winds to converge over the Chicago Thursday. The resulting pile-up or convergence of air helps brew especially well developed t-storms when—as is occurring Thursday—powerful jet stream winds blow cold air into the area aloft, encouraging air to rise with vigor. Parts of the area run the potential for severe t-storms in this environment.
Blistering early season heat is to bake the Southwest. Heat watches have been hoisted in Phoenix and the adjacent desert communities as 110° afternoon temps take hold later this week.
-Tom Skilling

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Area residents revelled Tuesday in 70° warmth. O’Hare’s official 71° high marked the 18th time this year that daytime readings have reached or exceeded 70°. But, even warmer temps are ahead Wednesday. And, the easterly winds of recent days have shifted SSE Wednesday, essentially paralleling the Lake Michigan shoreline. It’s a set-up which sends lake-chilled air into only the most eastern sections of Cook and Lake Counties.
A bit of convergence between the lake-cooled air and the warmer air inland—a process which produces heating through compression—may be enough to produce isolated 80° readings at the warmest inland locations.
The Plains broiled in 90° heat Tuesday. McCook, Neb. recorded 93° as did Garden City, Kansas. Powerful t-storms erupted in the late day heat bombarding Sutherland, Neb. with golf ball size hail. 60 m.p.h. gusts whipped Purdum, Neb. tearing shingles off roofs.
-Tom Skilling

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The sun never sets this time of year north of the Arctic Circle, 2,500 miles north of Chicago near Victoria Island in far northern Canada. That’s been the source of the eastern and central Midwest’s chilly air in recent days. Even the abundance of sun at such high latitude locations this time of the year isn’t able to overcome the lingering chill of winter. With north winds aloft in recent days directing the late season arctic chill south into Chicago, it’s little wonder this month is running more than 2° below normal—the coolest May here in 9 years.
Charged particles off a massive solar flare Friday produced one of the country’s best auroral displays in 15 years over the weekend. Northern lights were visible from the Chicago area south to Alabama, Texas, southern California and Arizona. Even a scientist wintering at the McMurdo Station in Antarctica reported auroral activity.

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If skies cleared out, Chicagoans might have had a glimpse of the Aurora Borealis overnight caused by a giant solar geomagnetic storm over the weekend. It was classified as an extreme event which disrupted satellite operations and electrical systems. Scattered light frost may greet early risers in the suburbs this morning, and even with abundant sunshine, today will be the second straight day this week high temps may not warm out of the 50s. With low pressure approaching from the west, readings are expected to warm into the 70s Tuesday and Wednesday accompanied by potentially heavy rains later Wednesday. Northeast flow cools the area Thursday and Friday. In advance of the next cold front a warmup into the 80s appears in store for NE Illinois next weekend. However, if preliminary longer-range computer projections are correct, the last week in May could be a cold one for Chicagoans, with north winds tapping Canadian cold air much of the week.

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NORTHERN LIGHTS ILLUMINATE CHICAGO'S SKIES LAST NIGHT

Chicagoans were treated to a dazzling display of the aurora borealis or northern lights early Sunday morning, following a strong solar flare on the sun on Friday May 13. The display was visible across much of the United States with reports of sightings as far south as southern California. According to NASA scientests, last night's aurora storm was caused by a coronal mass ejection (CME) propelled in our direction by an M8-class explosion near sunspot 759 that left the sun on May 13. Eighteen hours later it reached the Earth's atmosphere sparking the bright auroras.

Though far from a certainty, it is possible the aurora may be visible again tonight, especially in Canada, Alaska and areas north of Chicago.

One of our viewers Al Degutis took some spectacular pictures of the aurora from Woodstock and was kind enough to allow us to post them on our weather blog.

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Photo by Al Degutis

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Photo by Al Degutis

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Fast-moving undulations in the jet stream flow aloft will mark significant changes in Chicago’s weather pattern during the week ahead.
A northwest upper level flow will bring chilling Canadian air into the western Great Lakes today and Monday. A west to southwest flow steers low pressure over or just to the north allowing warm, moist air to briefly invade the area midweek. Northwest flow aloft returns Thursday followed by shift to the SW later Friday and Saturday.
Subtle variations in this high-level pattern can significantly impact the forecast for northeast Illinois. Computer models and forecasters are divided on the actual low pressure storm track which will be crucial to the Chicago projections. Should the low track follow a path through central Illinois, temperatures could be some 10 to 20° cooler than present forecasts. Either path will result in significant rainfall Wednesday.

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So dramatic was the north to south temp spread across the Chicago area Friday that it was as if two seasons were in progress simultaneously. Summerlike 80s reached north to Lansing (82°), Gary (84°) and Valparaiso, Ind. (85°). But, it was a different story farther north—chilly, damp and raw. At midday, readings varied 38°! In Kankakee, SW winds gusted past 30 m.p.h. and tropical air was in firm control, the temp had soared to 86°. While Waukegan reported light SE winds with drizzle in progress and a temp of just 48°. It was at that time, t-storms exploded to life over Grundy and Kendall counties and raced east across Will and Cook counties. The towering 46,000 ft. tall clouds turned skies black and pelted areas with marble-size hail. It took only 15 minutes for the rain to total 0.42” at Midway Airport and suburban Maywood reported a barrage of 1” hailstones.
Other clusters which flared to the east, swamped Warsaw, Ind. with 2.45” of rain in an hour.
-Tom Skilling

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Christopher Gazdic, a Columbia College student, captured these images of a Sears Tower lightning strike on video this past Wednesday morning, May 11 from his dormitory room. His video of the lightning strike is available at: http://www.fyrestudios.com/lightning/index.html

Many thanks to Christopher, for sharing these with us!
-- Tom Skilling

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It’s been a wild two days over the nation’s mid-section. Swarms of t-storms have battered nine states in t