WGN Weather Center Blog

After nearly two weeks of chilly weather, “spring-worthy” temperatures are poised to return to Chicago by the end of the week, but not before a late season frost threatens to whiten inland areas Monday night. By Tuesday daytime readings are expected to break the 60º mark and then steadily increase to highs in the middle and upper 70s by next weekend.
Despite the warm-up it appears that rainfall will continue to be scarce across northeast Illinois as the primary storm track remains anchored across the southern states. This is the primary reason that the last couple of storm systems have failed to produce significant rain in Chicago.
While two to four inch rainfall totals are expected across areas from Texas to Georgia and Florida this week, it seems that this area is relegated to receive nothing more than some scattered light showers or sprinkles early in the week.

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April hasn’t closed here with a daytime high any cooler than Saturday’s predicted 53° reading in a decade—since 1995, when Chicago recorded an April 30 maximum temp of just 50°.
Temperatures this time of year generally top out in the 60s. And, the cooler-than-normal air mass, with origins over Canada’s northern tundra, isn’t likely to leave anytime through early next week. Some of the area’s cooler inland nighttime lows will actually flirt with records in coming nights. Sunday morning’s 33° low is within striking distance of the record of 30°—a World War II era reading set in 1943.
The chilly air isn’t limited to the Midwest. A storm, with rains which bypassed Chicago to the south overnight, left 24.5” of snow at Jamestown, Colo., (in the mountains near Boulder) and 17.6” of late-season snow at Estes Park.

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Rain with the latest spring storm is only expected to swipe Chicago proper Friday night —and could all but bypass north suburban areas. That’s not the case in areas south. Rainfalls there are likely to increase sharply, though a suite of computer projections generated late Thursday suggest the heaviest totals—1” or greater amounts —are to occur 90 or more miles south of the Loop, in areas toward Watseka, Illinois and Rensselaer, Indiana and south. Severe t-storms are possible even farther downstate.
The blustery storm has whitened the mountains of Colorado, Utah and Wyoming in recent days and tugged a record chill into that area. While southern Alaska and the Yukon saw a 4th day of record June-level temps in the 60s and low 70s Thursday, record morning lows gripped Montana—including 9° at Phillipsburg and 16° at Havre. Daytime highs held 30° below normal in Wyoming.

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Talk about a topsy-turvy North American weather pattern! While Chicagoans dream of a return to the 80° warmth which teased the area just over a week ago, an unusual early season warm-up produced a third consecutive day of record breaking mild temps in Alaska. It’s a pattern strikingly similar to the one which last year produced that state’s warmest summer ever—along with drought conditions which fostered wildfires responsible for charring more than 6 million acres. Chicago’s high of 55° Wednesday was exceeded by record-breaking highs of 72° at Juneau and 65° at Anchorage.
Warmth of that magnitude forces jet stream winds well west and north—a situation which produces a very wavy North American jet stream pattern. Northwest winds blow from Canada’s arctic region south into the Midwest and are behind the sub-normal temps which have dominated here lately.

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A REPORT BY METEOROLOGIST RICHARD KOENEMAN FROM THE MOUNTAINS IN ASHEVILLE, N.C.

2.1" of snow here Saturday night into Sunday morning. Monthly total now 7.6" -- season total 14.7". So, more than half the season's snow has come down in April !!!

Yesterday's azaleas are today's memories.

Maylee is wearing her winter wardrobe again (this Sunday morning). But, never fear, later this week we'll all we wearing t-shirts again!

Maylee and Buddy preparing to bed down in front of the wood-burning stove.

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A swarm of small t-storms sprang to life at a furious pace Tuesday afternoon, pelting areas just west of Chicago with pea size hail and spinning up cold air funnels. The rate of thundershower growth was stunning. Radar images, void of precipitation as the afternoon began, were covered in less than an hour’s time, with a measle-like array of tiny precipitation “returns”. What’s more, the atmospheric set-up was perfect for cold air funnels. Counterclockwise-twisting eddies of air embedded within a huge, cold reservoir of air above the entire Midwest Tuesday—a condition meteorologists refer to as a vorticity rich environment—helped encourage the growth of rotating t-storms. Cold air funnels dipped from the bases of several of them near Rockford and DeKalb.
Cold air funnels rarely reach the ground, serving more as visual spectacles than threats, but are fascinating to watch.

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COLD AIR FUNNELS
Cold air funnels were reported late Tuesday afternoon in Rockford and near DeKalb. Here is an archived Ask Tom Why from 2001 explaining the meteorology behind the formation of a cold air funnel.

May 25, 2001
Dear Tom,
What are cold air funnels? Jeff Peterson, Huntley, IL

Dear Jeff,
A cold air funnel is a funnel cloud that does not develop in a typical severe weather environment. These funnels tend to form when there is large slow moving low pressure system in the upper atmosphere, similar to the one currently anchored over the Midwest. These cyclonic (counterclockwise) systems generate a lot of vorticity (spin) that enables the funnels to form. Cold air funnels get their name from the pocket of cold air aloft associated with these systems. The cold air produces a very unstable air mass, enabling towering cumulus clouds to rapidly grow into the showers and thunderstorms that produce these funnels. These funnels are weak and short-lived and usually do not touch down. Those that do reach the ground become weak tornadoes (winds often 50 m.p.h. or less) that generally produce only minor damage.

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The Chicago area has retreated into a more seasonable temp. regime in the past few days. But on Monday, Chicagoans welcomed 60s back to the local scene for a brief stay, making it the 16th daytime temperature this month to surge to 60-degree or higher. That’s a rare achievement for an April. In only one year—April 1955 with its 17 days above 60°—has an April had more 60s on the books 25 days into the month. With the exception of the three days from last Friday through this past Sunday, not a single other April 2005 day has finished below normal.
A shot of 60s returns Thursday away from the lake and again Monday of next week. But, the pattern appears a cool one the remainder of the week.
Monday was also unusual as only the sixth day this month with no lake cooling. On average, 76% of the days this month have featured easterly winds.

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In a time of the year when green thumbs are supposed to be in vogue, a late-season snowstorm has paralyzed the “thumb” area of lower Michigan with up to a foot and a half of snow piled into 3 to 4 foot drifts. The slow-moving storm, accompanied by howling north and northwest winds gusting to 45 m.p.h., brought heavy, wet snow to portions of areas from Michigan and Indiana southeast to the western Carolinas with up to 6 to 12 inches of snow expected in portions of the Detroit and Cleveland metro areas.
The storm’s western fringe delivered an inch or two of snow to Lake and Porter counties in northwest Indiana early Sunday, though sun and temps in the 50s brought its quick demise.
Today’s highs in the lower 60s will likely mark Chicago’s temperature high point this week. Reversing a three-week trend of predominately sunny, warm weather, April’s final week is expected to close with a string of days in the 50s.

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Heavy snowfall started to fall Saturday night over Lower Michigan and northern Ohio and is expected to continue today with anywhere from 5 to 15 inch storm totals forecast. Saturday over northeast Illinois temperatures hovered in the 30s a good part of the day, ending up with most highs reaching the lower 40s. High temperature at Northerly Island was 38°. These readings along with northerly winds gusting in excess of 30 mph gave afternoon wind chills in the mid to upper 20s. The National Weather service had issued freeze warnings for most of Illinois early this Sunday morning. It looks like the week ahead for Chicagoans will see high temperatures staying in a fairly narrow range—averaging about 7° below normal. Clouds and rain are likely Later Monday night through Tuesday into Wednesday and again later Friday into Saturday.

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We’re heading into the 17th weekend of 2005—a time of year when highs ought be in the low 60s. Yet, Chicago’s predicted temps Saturday and Sunday will hold to just 41° and 45°—readings which are cooler than the 41° and 54° highs which occurred back on Jan. 1-2, the year’s first weekend.
This puts the area in rare temperature territory. Together with Friday’s 46°, additional 40s both Saturday and Sunday mean the city is in the midst of a three-day string of 40s. That doesn’t happen often. The infrequency with which three consecutive days in late April hold to the 40s is clear from Chicago weather records. Only four such periods have been recorded here since 1940.
These unseasonably chilly temperatures along with cloud-level readings only in the teens and low 20s mean at least some of the snowflakes which form in these clouds may survive the trip down to ground level. If so, they would be the first so late in a season since 1994.

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A dusting of snow greeted residents of northern Michigan and sections of
the state's Upper Peninsula Friday. The late-season snow has occurred
within the same unusually chilly late-season air mass which could
produce near freezing temperatures in sections of the Chicago metro area
away from the lake Friday night - and subfreezing readings Saturday
night away from the lakeshore. Our thanks to meteorologist John Dee, who
forwarded this snow image from a Michigan trail cam he operates south of
Houghton in South Range. John reports this is the first measurable snow
to fall in that area since March 20 and the first flurries to be observed
there since March 31. He notes that parts of the U.P.'s Keweenaw
Peninsula have seen 280" of snow this snow season - though March and
April have hosted above-normal temperatures.
A few wet snowflakes or some mixed ice pellets can't be ruled out
in lake-effect rain showers predicted in the lake-effect precip belt of
extreme northeast Illinois and northwest Indiana Saturday. In addition,
some instability showers may develop in scattered inland sections of
Illinois and Wisconsin, given the rapid vertical temperature drop predicted
Saturday as a result of the arrival of unusually cold air aloft. They
too could feature some mixed ice pellets of a snowflakes. Metro area
temps this weekend are to run more than 30 degrees below the levels
observed away from Chicago's lakeshore last Saturday and Sunday.
-- Tom Skilling

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Until Thursday, this spring’s temperature surpluses had been building at an impressive rate. The day’s 57° high and 42° low produced the first below normal daily average temp here in 24 days. And the weekend ahead looks even cooler. Daytime highs will hold to the 40s—a level +20° below normal and the first daytime readings to remain that cool this month. Those temps would be more than 30° chillier than Saturday and Sunday a week ago. The change to cool weather ends a 24-day run of temps which finished at or above normal.
This marks a dramatic turnaround in the temperature trend this spring. Since the start of the season on March 1, temps have averaged 2.1° above normal, warm enough to rank 35th warmest of any spring in 135 years. April’s remarkable warmth has contributed mightily. Until now, this month alone has averaged 8° above normal.

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Photo by Kathleen Mahoney

We'd like to thank Kathleen Mahoney for sharing the "moonlight and magnolias" photos taken from her backyard in Oak Park. A sure sign that spring is in the air!
--Bill Snyder

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T-storms spared Chicago Wednesday. The city escaped with little more than sprinkles. But it was a different story just south. A sharp cold front, which swept across O’Hare at 10:27 a.m., shifted winds northeast, slashing temps 15° in the hour which followed, and setting the stage for explosive t-storm development across Chicago’s far southern suburbs. Wind-driven downpours were so heavy in the storms—some 40,000 ft. tall—that sections of western Kankakee county near Bonfield were swamped by 2.90” of rain. Hail and damaging winds occurred from Peoria east into central Indiana. By evening, 135 reports of severe weather had reached NOAA’s Oklahoma-based Storm Prediction Center from sections of 10 states from Texas east to Pennsylvania.
Record snow made headlines in Montana. Billings was walloped by 10.8”—the heaviest late season accumulation in that city since 1997.

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The Chicago area’s recent warmth has been unprecedented. When averaged, the 83° and 81° highs Monday and Tuesday, rank second warmest of any April 18-19 since 1871. The same period in 1985 is the only one warmer. The recent warmth has capped a string of 23 days with temps at or above normal and makes April, 2005 the 4th warmest in 135 years.
Chicago has not been alone in enjoying warm weather. Twin Cities’ residents are in the midst of their warmest April ever. And, a series of new temp records were set in Michigan Tuesday, including the 84° at Traverse City, as well as the 81° high at Sault Ste. Marie and Lansing. Detroit topped out at 83°—also a new record.
The warm spell’s demise was accompanied by violent weather to Chicago’s west Tuesday. Tennis ball size hail fell near Hyannis, Neb. while 3.50” of rain doused Stacyville, Iowa causing basement flooding.
-Tom Skilling

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All but the immediate Lake Michigan shoreline was treated to summerlike warmth Monday. In just 9 hours time Monday, the temp here surged 38° from the day’s low of 45° to 2005’s highest reading to date—83° at 2:15 p.m.! That temperature was the highest here in 7 months (since 85° on Sept. 23) and the year’s second to reach or exceed 80°. Only four other April 18’s in the past 135 years have been warmer. The 83° peak reading equaled the normal high which occurs here on July 3 and exceeded Monday’s highs in Miami (80°), Key West (79°), Tampa (78°), New Orleans (77°) and Las Vegas (79°). The unseasonable warmth fueled an outbreak of severe t-storms in the Plains and western Midwest. Hail the size of golf balls covered the ground at Waco, Neb.
While the central U.S, enjoyed warmth, at the other end of the spectrum, McGrath, Alaska recorded a low of -18° Monday—a reading 38° below normal and a new record.
-Tom Skilling

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Chicago’s second and third 80° days of 2005 are likely to occur today and again Tuesday. Warming southwest flow digs in today and continues Tuesday. Higher dew points also accompany the warmer air, especially Tuesday. With the approach of a cold front, showers and thunderstorms are likely to develop over northeast Illinois later Tuesday afternoon and continue that night. With a shift to north winds behind the cold front, Wednesday will see temperatures moderate considerably, and for the rest of the week temperatures will be closer to mid-April normals. However, if projections are correct, temperatures will average above normal until Friday. This would mark 22 consecutive days with above-normal readings to start this April, far exceeding the all-time record of just 10 above normal days beginning April in 1871 and 1969. The southern and central Plains continue to be under the threat of severe storms today and Tuesday.

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Not a day with below normal temps so far this month—16 days straight as of Saturday and still counting! According to Chicago’s climatological data expert Frank Wachowski, the longest previous stretch of consecutive days at or above average at the start of April was 10 back in 1871 and 1969. So April 2005 in Chicago has established a record and the end is not in sight. The first half of this month temperatures have averaged nearly 7° above normal and if forecasts pan out, the warmest is yet to come! The first three days this week (Sunday-Tuesday) readings are projected to average nearly 20° above normal. By week’s end Chicago’s record April start of consecutive days averaging at or above normal may have reached 23! A cold front is expected to sink south into central Illinois later Wednesday followed by a persistent north to northeast flow that should cool temperatures significantly, but even then readings may average at or slightly above normal.

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Never over the 134-year term of weather records here has April started with more consecutive days of near or above-normal temperatures. Despite the relative chill of recent days, the month still hasn’t produced a single high below 50°. There hasn’t been an April which has failed to log at least one day with highs in the 40s or lower. The opening 15 days of the month are nearly 7 degrees above normal. And, that surplus is likely to grow in the days ahead as 2005’s most extended period of mild weather takes up residence.
Cloud cover returns Saturday after a three-day absence. High clouds off t-storms, which are to flare upstream (to the northwest) of Chicago in Iowa and Minnesota, begin filtering the day’s sun—then become thicker and better-developed Saturday night, when an incoming disturbance threatens clusters of showers and t-storms. The degree to which Sunday warms is dependent on how soon clouds depart and the strength of lake winds.

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It’s a very unusual air mass able to produce relative humidities low enough to flirt with the all time record. But, that was the situation in Chicago Thursday. Not only were skies 100% cloud free for a 2nd consecutive day, humidities here were lower much of the day than in the desert Southwest. At 6:05 p.m. Thursday evening, Chicago’s relative humidity dropped to just 14%. On only three occasions since weather records began here in 1871—on May 10, 1934, April 11, 1956 and April 8, 1971 —has the air been any drier —and, on those occasions, by only 1%! Air that dry cools quickly because there is little moisture to retain heat. But, the same air heats rapidly once the sun rises. That’s one reason temps soared to 66° Thursday afternoon in the Fox Valley. It also explains the wide 30° spread between Thursday’s 63° and 33° extremes at O’Hare. The normal range is 57° and 37°.

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Sunburns are up this year and the recent spate of clear, haze-free days is a major factor. That’s the word from dermatologist Dr. Bryan Schultz, who says the number of patients reporting burns is among the highest he’s seen in years. He’s been in the area for more than two decades and measures the strength of the sunlight at his Oak Park office each day. “Sunlight intensity is the strongest I’ve seen in some time.” says Schultz.
Exceptionally low humidities have reduced haze levels and may be playing a role. Schultz says sunburns may be aggravated by certain medications which make the skin especially sensitive to sunlight.
Temps Wednesday only reached 54° in Chicago—a reading which equals the highs on April 7 and 12, the coolest daytime readings this month. April 1-13, 2005 ranks 9th warmest of any comparable period since 1871. The month has yet to produce a single high below 50° to date, joining only two other Aprils in the past 134 years to do so.

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Chicago was hit Tuesday by the heaviest rains to douse the area since January as temperatures tumbled. O’Hare’s 0.63” was the largest total at the site since 0.89” fell on January 12. Only four April 12 rains since official measurements began here in 1871 have been heavier. The area around Midway Airport recorded 0.61”. But, hardest hit of all were Chicago’s west and southern suburbs. 1.58” of rain was measured at the National Weather Service office in Romeoville and more than an inch rain fell downstate at Champaign (1.10”), Springfield (1.01”) and Galesburg (1.17”).
The powerful storm behind Tuesday’s temperature plunge prompted afternoon severe t-storm watches across central and southern Illinois. Small tornadoes are reported to have touched down in Montgomery and Franklin counties in southern Illinois, between Mt. Vernon and Carbondale. Hail accompanied other storms there.

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