WGN Weather Center Blog

Warmer than normal temperatures have had an incredible run here. October, which ended at midnight, was the fifth consecutive month to produce a surplus, finishing more than 3° above normal. By almost any measure, the persistence and magnitude of the warmth places the current spell among the most impressive on the books. Of the 153 days since June 1 in Chicago, 107—or 70% of them—have posted surpluses. The period from June 1 through Oct. 31 averaged 69.7° in the city—3° above the long term average here since 1871. And, Chicago isn’t alone. Illinois’ state climatologist Dr. Jim Angel reports statewide temperatures over the same period rank 7th warmest of 110 comparable periods on record since 1895.
Trick or treaters faced the area’s wettest Halloween in 10 years Monday night, even though rainfall at Midway Airport had only reached 0.17” by late evening. The rain failed to prevent October from posting the 8th consecutive monthly rain deficit in a row.

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There will be a seamless transition to November as the city’s current spell of mild, dry weather continues. The 60º-plus mildness of October’s final days should persist through November’s opening week, setting the stage for some possible record-breaking events. Since 1871, the most consecutive 60º-plus days at November’s start is five, something that has happened only three times—most recently in 1978.
The area’s drought continues, and October 2005 will go into the books as the eight consecutive month with below-normal precipitation. Except for today’s showers, which may put an unfortunate damper on Halloween activities, little if any rain is expected the remainder of the week.
In contrast, up to 2 feet of rain from the remnants of Hurricane Beta is inundating portions of Nicaragua, Honduras and El Salvador. Forecasters are closely monitoring the dying storm, which could re-energize upon entering the eastern Pacific.

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The 2005 hurricane season continues to produce storms at a record pace. Hurricane Beta is the season’s 13th, breaking the old record of a 12 set back in 1969. Beta should make landfall this morning on Nicaragua’s northeast coast with winds approaching the 111 m.p.h. Category 3 threshold. However, Beta’s legacy may well lie in the aftermath of its torrential rainfall that could exceed two feet over the mountainous terrain of Nicaragua and Honduras, causing massive flash flooding, mudslides and potentially a large loss of life.
Meanwhile, Chicago is facing an unusually mild November start dominated by highs in the 60s, at a time of year when cold, blustery weather along with the season’s first snow flurries would not be considered unusual. Two periods of rain are possible, one tonight into Monday and again Thursday, but neither will make a significant dent in the area’s extreme drought.

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Chicago’s 2005 growing season, defined by the number of days between the last and first frost, officially ended early Friday—nearly two weeks later than its normal Oct. 15 conclusion. A typical growing season here runs 187 days. But this year’s drought-plagued season extended an extra three weeks to 208 days.
Earth is headed for one of its closest encounters with Mars in more than two years Saturday night. The two planets won’t be closer than the 43.1 million miles which separates them at 9 p.m. tonight until the year 2018. Astronomer Dan Joyce advises that Mars will appear above the eastern horizon as a fiery yellow point of light at the time the “close” pass takes place.
The metro area’s coldest autumn temperatures to date were behind the widespread frost and included 31° at O’Hare Airport—but readings were as low as 23° in west suburban Aurora.

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November may only be four days away, but a surge of milder air more typical of late September promises to deliver the area’s highest daytime temperatures in nearly two weeks this weekend. With frost visible in many parts of the metro area as Friday dawns, it’s clear the warmth isn’t here yet. Daybreak readings hover at Fall 2005’s coldest levels to date. For eight consecutive days, daily highs have remained below 60° and Friday’s predicted 59° may well become the ninth. But, strengthening southwest winds return temperatures to within striking distance of 70° this weekend.
The recent chill has been unable to dislodge Fall 2005 from its perch as the Chicago area’s 22nd mildest autumn of the past 135 years—and the warmest fall here in 32 years.
Hail accumulated 4” in Texas thunderstorms Thursday while 6-10” of snow is to blanket the mountains of Wyoming and Utah Friday.
-Tom Skilling

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Lake Michigan waterspout off Foster Avenue Beach and the Montrose Avenue Pier along Chicago's lakefront Thursday morning

This waterspout was captured by Ryan Szekeres out over Lake Michigan at 11 a.m. Thursday morning. Unusually chilly air over the lake's comparatively warm water contributed to the instability (the steep decline of temperature with height in place at the time of this vortex's formation) behind the waterspout's formation. Lake water temperatures off Chicago at the time averaged 57-degrees while readings just a mile aloft were only 27-degrees---a nearly 30-degree temperature drop! It's at least the second time in a week that a waterpout has been spotted off the Chicago shoreline.
--Tom Skilling

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The final lake-effect rains of this cool cycle pull out of the city later Thursday—but, not before some of the chilly showers ride NNE winds, blowing several thousand feet above ground-level, as much as 30 to 40 miles inland. A gradual breakdown in these winds is behind the predicted end of cloud and precipitation formation.
The wind-free environment predicted to take hold Thursday night threatens fairly widespread frost before a multiday warm-up begins Friday. Highs are to surge from the 50s to the 60s Saturday and near 70° Sunday. It’s to become the biggest “warm-up” here in two weeks. 60% of years since 1970 have produced at least one additional 70° beyond this date.
The rebound couldn’t occur at a better time. With only 19% of possible sunshine recorded over the past week, daytime highs have averaged 51.2°—a reading 17° lower than a comparable period one year ago.
-Tom Skilling

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Floridians, subjected to eight hurricanes in the past 18 months, faced a new challenge Tuesday—record-breaking cool air in the wake of deadly hurricane Wilma. With electricity still out in an estimated three million homes, the chill was unwelcome and uncomfortable. Record morning lows included 48° at Vero Beach, 49° in Melbourne and 52° at West Palm Beach.
The big news Tuesday in the Mid-Atlantic and New England was wind-driven rain and the season’s first snowstorm. Rains fell horizontally in Boston in howling northeast winds clocked to 52 m.p.h. Buoys operated in the Atlantic by NOAA rocked in 20-25 ft. swells which tore at the coastline. Meantime, an injection of cold air turned rain to wet, tree-snapping snow responsible for power outages from interior Pennsylvania, western and northern New York and interior New England.
-Tom Skilling

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Photographed Monday morning (Adler Planetarium in the foreground)

Photo courtesy of George Holman and Kami Chin

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A massive nor’easter, pounding the country’s Mid-Atlantic and Northeast region, undergoes the meteorological equivalent a fuel injection Tuesday once the remnants of Hurricane Wilma become part of its massive 2,200 mile diameter circulation. An area from Chicago, where northerly winds promise another day of sporadic lake rains, to Boston, home to 60 m.p.h. NE winds likely to generate two-story waves which tear at the nearby coast, is under this system’s far-reaching grip.
New York City has already recorded the equivalent of four Octobers worth of rain and may soar close to its all time 16.85” monthly precipitation record set in September, 1882 with today’s rain. But, cold air wrapping south on the storm’s backside shifts rain to snow Tuesday and threatens a tree and powerline-snapping 6-12” accumulation in the higher elevations of Pennsylvania, New York and northern New England.

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Dominating much of the eastern United States, a huge low pressure system over the Ohio Valley will steer cold Canadian air into northern Illinois at the same time it guides Hurricane Wilma through southern Florida today.
An unexpected break in the clouds Saturday night allowed temperatures to drop below freezing in areas to the west and south away from the lake, effectively ending their growing season—Aurora hit 24° while Rockford, Romeoville, and West Chicago all recorded lows in the upper 20s.
Tornadoes hit southern Florida ahead of Wilma Sunday, but its fast movement will probably restrict today’s rainfall totals in its path to the 2-4 inch range. As the low drifts east the first half of the week, northerly winds will prevail over Chicago, holding highs 5-10 degrees below normal. By midweek, Wilma will be a weakening low in the Atlantic, and southwest upper winds over the Plains will be a prelude to a Chicago warm-up next weekend.

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While Hurricane Wilma swamped northeastern Yucatan with two days of torrential downpours (Isla Mujeres just off the northeast tip had unconfirmed reports of an incredible 64.47 inches and it was still raining Late Sunday afternoon), a strong jet stream steered this season’s coldest air into the western Great Lakes. A persistent jet stream pattern flowing across Canada’s Northwest territory and sweeping Hudson Bay before turning south across Lake Superior establishes itself with the resulting air mass tapping some of the coldest source regions to the north and then modifying as it makes the journey south. North winds and very cold air aloft will create unstable atmospheric conditions the next couple days, the most intense being today with a forecast of extensive cloudiness and an almost continual threat of showers.
Meanwhile in the Caribbean, the record 22nd named storm of the season, Tropical Storm “Alpha” crossed Hispaniola.

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Floridians aren’t likely to experience anything close to the fury Hurricane Wilma unleashed Friday on Mexico’s northeastern Yucatan peninsula—a region dubbed the Mayan Riviera. The fickle late season atmospheric behemoth, only days ago the Atlantic Basin’s most intense hurricane in terms of barometric pressure, roared across Cozumel Island around 3:30 p.m. Friday. A NOAA weather buoy moored in the western Caribbean, 170 miles east of the Yucatan, clocked 96 m.p.h. gusts and detected 36 foot waves on Wilma’s periphery earlier in the day. Instrument payloads dropped by an Air Force Reserve reconnaissance flight suggests the vacation mecca of Cancun may well have absorbed catastrophic 150 m.p.h. winds.
Wilma’s energy-depleting en-counter with the Yucatan lasts into Saturday. The storm should reach Florida toward Monday at Category 1 or 2 intensity (possessing 74-110 m.p.h. winds).

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Another rain opportunity fizzled across the Chicago area Thursday as a batch of showers moved through central Illinois leaving the northern metro area high and dry, while teasing south sections with some very light showers. This area has not received significant rain in nearly three weeks and remains locked in extreme drought.
The cooldown did materialize however, with Thursday’s highs failing to rise out of the mid-50s. Readings will tumble from there and the city’s first two World Series games since 1959 should be played in chilly, damp conditions with temperatures in the 40s along with a threat of some scattered light showers.
In the northwest Caribbean, a much larger Hurricane Wilma was taking dead aim at Mexico’s Yucatan Peninsula. Thursday evening, the storm was on the verge of regaining Category 5 strength and producing gusts to 86 m.p.h. and 34 foot waves about 175 miles off the coast.

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What a change! The area is finally in the grip of cool autumn air. Still cooler temperatures are due this weekend—potentially the chilliest in more than five months. Sox fans face weather Saturday and Sunday more typical of the fall football season than of many World Series. By Sunday, daytime highs may fail to reach 50° for the first time since May 2 of this past spring.
Thursday’s thickening overcast and strengthening northeast winds are to carry rain into the area, part of a storm which buried Colorado mountaintops under as much as 8” of snow Wednesday while bombarding
Dodge City, Kansas with 2” diameter hail in powerful thunderstorms. A tornado touched down at 4:36 pm in Meade County, Kansas in the incoming system’s warm sector.
Wet weather reaches Chicago Thursday. Totals will be heaviest to the south, but up to 0.50” is predicted in the city proper.
-TOM SKILLING

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Chicagoans enjoyed an eighth October 70°+ day Tuesday—warmth more typical of mid-September than mid-October. O’Hare’s 73° high paled in comparison to Oklahoma City’s 92° and Norfolk, Nebraska’s 89°—both records. But, one of October’s infamous temperature crashes is sweeping the nation’s heartland. Many of those same areas will find readings 20 or more degrees colder in coming days as clouds and blustery rains sweep in with a northeast-bound autumn storm.
Far to the south, Hurricane Wilma underwent explosive intensification late Tuesday as the storm’s winds soared to 110 m.p.h. and its eye shrunk to only 8 miles across—a feature found in only the most fearsome hurricanes and referred to by forecasters as a “dreaded pinhole eye”. Wilma may attain top-tier Category 5 status in the Caribbean and, though not quite as strong, remains a serious threat to Florida this weekend.

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Floridians and residents of Mexico’s Yucatan Peninsula have good reason to monitor Tropical Storm Wilma in coming days. The late season storm faces no obvious obstacles to developing into a major hurricane over the western Caribbean and appears on a track which may affect both areas. The latest forecasts have Wilma’s sustained winds reaching at least 115 m.p.h. thanks to exceptionally light winds above the storm, which eliminate the kind of wind shear—the shift in wind direction and speed in the storm’s environment—responsible for disrupting hurricane intensification. Sea surface temperatures beneath the storm remain very warm, and to impressive depths—another factor which favors strengthening.
Of the 22 hurricanes since 1851 known to have come ashore in the U.S. beyond October 18, 17 have made landfall in Florida. Their intensities have ranged from Saffir-Simpson scale Category 1 (winds 74 to 95 m.p.h.) to Category 4 (winds 131-155 m.p.h.) intensity.

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Another testament to the warm autumn that Chicago is experiencing has been the total absence of overnight lows in the 30s so far this season. Not since 1963, when the season’s first low in the 30s finally occurred on Oct. 29, has this autumn benchmark been so delayed. Temperatures in the upcoming week should continue the above-normal trend that has dominated this season so far.
Area rain deficits continue to increase, though prospects for some significant precipitation are shaping up for later this week as a storm system passes through the Midwest. In contrast, more than a week of flooding rain is finally ending in the Northeast, where rainfall totals so far this month include 13.26 inches at New York City’s Central Park and 10.76 inches at Concord, N.H.
Meanwhile, interests along the Gulf Coast are keeping a watchful eye on Tropical Depression 24 in the Caribbean that is expected to strengthen into Hurricane Wilma later this week.

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Eight days of unrelenting heavy rain has set portions of New England awash. Rain, while continuing intermittently today, is finally diminishing.
Persistent onshore winds, frequently above 40 m.p.h. in recent days, built towering ocean waves that have pounded coastal areas and left New England beaches eroded and damaged.
Eight-day rain totals through Sunday afternoon have climbed to 10-16 inches from northern New Jersey to southern Maine.
1,600 miles to the south, a new tropical cyclone is intensifying over the 88° waters of the Caribbean Sea. The National Hurricane Center advises that Hurricane Wilma—the season’s 21st named storm—will emerge this afternoon, and then begin a northward trek that might threaten Cuba toward the weekend. Additional named storms, should they develop, will default to Greek letters (Alpha, Beta, Gamma, Delta, etc.)

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Following a summer of meteorological excesses—extreme heat and severe drought—Chicago’s weather has progressed into a mild and dry autumn.
Those weather anomalies, however, are much easier to bear in the fall.
When the temperature climbs 12 degrees above normal in mid October, as it did yesterday, the result is a pleasant afternoon with readings in the middle 70s. When that same anomaly occurs in mid summer, however, the city swelters with temperatures in the middle or upper 90s.
Moisture deficits, too, are less damaging to vegetation in the autumn than they are in the summer because plants are heading into dormancy.
A lingering impact of Chicago’s summer drought will be muted foliage displays on moisture-stressed area trees. Premature shedding of leaves and less vivid coloration are unavoidable results of long-term moisture deprivation.

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On occasion, extreme weather events occur so gently and so unobtrusively that we fail to notice them. In that vein, Chicagoans will be surprised to learn that they have been experiencing a period of record-setting warmth since Sept. 1.
Meteorological autumn (the months of September, October and November) is now about half completed, and temperatures through the first half of Chicago’s fall season this year have been proceeding at a sizzling pace.
Never in 135 years of weather history (1871 to the present) has the city’s temperature, averaged for the period Sept. 1 through Oct. 13, been warmer than 2005’s value of 68.9º as registered at Midway Airport for that 43-day period.
Computer models suggest the mild pattern remains in place in upcoming days. Daily high temperatures will average about 7 degrees above normal through the next week.

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Cloudiness and lingering spits of drizzle and very light rain are still possible today, but the sun is also likely to break through the overcast at times, and those tentative rays of sunshine are harbingers of brighter days and warmer temperatures ahead.
Computer models are in agreement that a major weather pattern change is in the works. For Chicago and the Midwest, this is a signal that the recent spell of gray dampness and cool temperatures is about to give way to higher temperatures.
The warm-up begins today, strengthens tomorrow, then is blunted by a brief return of cooler air over the weekend before a vigorous and more enduring warm-up arrives early next week.
It’s even possible that Chicago’s temperatures might hit 80º by next Wednesday —an event that occurs here on only about one day in 14 in the middle of October.

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