TOM SKILLING

Chicago's 9-day run of temperatures well above normal came to a blustery and unceremonious halt Thursday. That warm spell  had generated seven of 2013's nine days with 80s, including the year's only official 90-degree reading.

In sharp contrast, Thursday managed a high temp of only 54-degrees, 20-degrees below the peak reading which had occurred only the day before---a temperature which was 18-degrees below normal. The reading equaled April 2's  normal high---a  temperature most likely to occur 7 weeks earlier!

And, as if the chill wasn’t enough, the unseasonably cool readings rode wind gusts which topped 50 mph into the city. The powerful flow, which ran the length of Lake Michigan into Chicago, piled up 13 ft. waves which pounded the Lake Michigan shoreline here.

Friday’s unlimited sun and lighter winds welcome---but the temp rebound they generate is to be modest and well off historic norms

Temperatures surge back into the 60s Friday afternoon thanks to nearly unlimited sunshine. That's a 10-degree improvement over Thursday’s chilly maximum---but still well below the normal high which is 73-degrees on May 24.

Powerful t-storms rake the southern Plains, some with 110 mph straight-line gusts; others spin-up tornadoes

Downpours swept tornado- ravaged Moore, Oklahoma early Thursday while powerful new thunderstorms later in the day sent high winds, hail the size of tennis balls and a new flock of tornadoes into the southern Plains. The twisters' target this time was west Texas. Winds there gusted to 110 mph at Rotan; 105 mph 9 miles west of Albany, 92 mph a mile southeast of Jayton, and 80 mph at Cone---all in Texas.  The storms blew roofs off houses in Abilene.

It's official! This spring's rainfall is now truly one for the books.

With just over a week left in the meteorological spring season, which runs from March 1 through May, the 14.29" which has fallen to-date, makes this Chicago's 2nd- wettest on record the past 142 years.

Wednesday downpours, some thundery, contribute to a number of 1.50"+ totals

Wednesday's selective downpours totaled 2.15" at Wilmette, 1.80" at Northfield, 1.73" Niles, 1.62" Glencoe and  1.33"  at O'Hare. The latest round of t-storms has pushed May 2013's monthly tally to 3.61", while the spring total is 168% normal.

“Full-fetch” north/northeast winds shave temps by nearly 20-degrees Thursday; 9-day above normal streak ends as April-level chill takes over

Chicago temps take a big "hit" Thursday as brisk north/northeast winds travel into the city after a near-280 mile trip over Lake Michigan's chilly waters.

The set-up is predicted to slash readings by up to 20-degrees---compared to Wednesday's temps--- and will take readings down to the 50s (and even some upper 40s along Lake Michigan), level which equal the normal temps found in April.

The chill is to end the longest string of consecutive above normal days---9 of them--- in the 4.5 months since January.

Our once chilly spring has wasted no time in playing catch-up! 2013, with nine 80s to its credit through May 21, is now well ahead of the long term average of 5 such days. And while, sharp cooling back to April-level temps is to hit Thursday with the arrival  of gusty north to northeast winds, strong warming is to return 80s and higher humidities to the area next week.

Rainy spells and sporadic thundery downpours to bolster impressive late Monday/Tuesday precip totals

Waves of showers and thunderstorms greet area residents Wednesday and Wednesday night. It’s a development likely to add to the impressive rain tallies observed over a wide swath of the area Monday and Tuesday .

Grundy County's Braceville reported 3.44" during that period while 2.11" came down at Lisle, 2.05" Glen Ellyn; 2.04" Naperville and 1.99" at Villa Park.

Weather Service storm survey teams rate the Newcastle/Moore, Oklahoma twister an EF-5; only 59 comparably strong tornadoes on the books nationwide since 1950

It’s official. The deadly and devastating tornado which roared into Newcastle and Moore, Oklahoma has been rated EF-5 and joins the short list of 59 comparably devastating twisters on the books across the U.S. at the Storm Prediction Center since 1950.

The year's second warmest Chicago temperatures fueled powerful, downpour and wind-generating thunderstorms which lashed much of the metro area overnight.

High temperatures Monday hit 92-degrees at Midway and 89 at both O'Hare and Chicago's lakefront, where the reading was 18-degrees warmer than Sunday’s shoreline 72. The warmth and influx of Gulf moisture laid the atmospheric foundation for the storms which followed overnight.

The storms hit many areas with torrential rainfall and unleashed wind gusts clocked as high as 61 mph in Chicago's west Loop, 57 mph at the offshore Crib, 53 mph at Douglas Park in the city, 47 mph in Old Town and 56 mph at Park Forest.

Rainfall was torrential. Of the 1.16" measured at Carbon Hill in Grundy County, 1.10" fell in just 35 minutes. Lombard's 1.64" tally fell in just 75 minutes.

Chicago area storms generated by same spring system responsible for the devastating Oklahoma tornadoes; hundreds of severe weather reports including dozens of tornadoes have been tallied by Storm Prediction Center past 2 days

The storms which swept Chicago overnight were products of the same huge spring low pressure system behind the devastating Newcastle, Moore and southern Oklahoma City tornado, one of the worst and mostly deadly twisters to hit a state in which tornadoes are no strangers.

Though official National Weather Service storm surveys are to take place beginning Tuesday, the mammoth tornado, at times more than a mile and a half wide as it churned along a 20 mile path over its 40 minute meteorological reign of terror, was believed to be of AT LEAST “EF4” intensity---suggesting winds of 160 to 200 mph if not higher.

The twister touched down at 2:56 pm Monday afternoon and was on the ground until 3:36 pm according to preliminary reports. The death and devastation it produced covered at least 30 square miles, involved an estimated 4,000 homes and produced a “debris ball”----a radar return produced by airborne debris--- which ranked among the largest forecasters have seen.

Debris hoisted aloft by the gargantuan wind machine traveled 250 miles to Branson, Missouri!

Track of the Tuesday "Sooner State" tornado shockingly close to a huge May 3, 1999 twister there; Monday's was the third major tornado to hit the same swath of terrain in the past 14 years

The path followed across central Oklahoma by Monday's twister nearly paralleled a  benchmark May 3, 1999 tornado, which killed 26, was on the ground 36 miles and generated damage put at $1.1-billion dollars.

Two other twisters---including Monday's--- have devastated the same region of the state since the 1999 F-5 twister. That storm produced Doppler-scanned winds of 318 mph---the strongest ever measured in a tornado.

Veteran severe weather researcher reports even the twister’s "sound" was different and particularly ominous

One of the country’s leading severe weather researchers and a 41 year veteran of storm chasing, had a first-hand view of the tornado's trek across Oklahoma Monday. Describing the vortex of the tornado as rain-wrapped, Dr. Chuck Doswell reports the sound the twister made was like no other tornado he's observed in his career.

While most tornadoes he’s observed over his more than four decades of tracking twisters produced a sound comparable to a "waterfall", Monday’s storm, he reports, generated a far more menacing sound, more like a fleet of jet fighters---an disturbing sound which may well have been a by-product of the cataclysmic devastation it was producing.

Rains aren't over in Chicago; several new rounds of downpours to hit Tuesday night into Thursday morning

Sunshine is likely to be out a number of hours Tuesday.  But the threat of additional downpours isn’t over.

Conditions capable of spinning up active or severe storms remain in place, and several additional waves of drenching rains are a good bet Tuesday night and again Wednesday night into Thursday morning.

Lakeshore cooling persists a second day Saturday. Friday produced a temperature spread of up to 30-degrees between Chicago area beaches and the warmest inland locations.

While Kenosha and Highland Park, on the receiving end of easterly winds coming off chilly lake waters, ended up on the low end of the thermal ledger Friday with highs of 56 and 57-degrees, both Kankakee and DeKalb were warm, posting 85 and 82-degree peak readings respectively.

Saturday highs will repeat that trend with shoreline and beach temperatures holding to the low 60s while inland locations, head toward their warmest weekend temperatures since last September (37 weeks ago). Highs there will reach the mid 70s while near 80-degree readings are likely at the warmest south suburban observation sites.

80s return to the city Sunday, Monday and Tuesday after 2 day absence

Strengthening south to southeast winds return much of the city and inland areas to the 80s Sunday—the beginning of a fresh three-day string of 80s likely to run through Tuesday. It's conceivable a fourth 80-degree high may occur Wednesday.

80-degree or warmer daytime highs Sunday, Monday and Tuesday would mark the 6th, 7th and 8th time this year that temperatures have moved into the 80s.

Isolated thunderstorms unleash Friday’s heaviest downpours south of the city; spotty storm development ahead Saturday and Sunday

Isolated thunderstorms produced by towering cumulonimbus clouds (i.e. thunderheads), which reached heights up to 46,000 ft. Friday according to Doppler radar scans, are likely to re-develop in scattered fashion both Saturday and Sunday.

Though only a fraction of the full Chicago area may see these storms, the moist environment in which they’re developing could produce brief downpours.

Predicted warmth comes as meteorological spring 2013—currently the coolest in 17 years—enters its final two weeks

The predicted weekend warmth comes as the coolest meteorological spring season of the past 17 years moves into its final two weeks.

Since March 1—the start of meteorological spring—Chicago’s temperature has averaged 43.7-degrees.  That’s a reading 1.6-degrees below the long term average and 10.4-degrees cooler than the same period a year ago.

"Trying" pollen season produces a 13th consecutive report of “high” tree pollen values Friday

This pollen season has been a miserable one for far too many area allergy sufferers.  Pollen counts are generated Monday through Friday. Friday marked the 13th consecutive report in which the tree pollen value taken by Dr. Joseph Leija and distributed by Loyola-Gottlieb Memorial Hospital was categorized as “high”.

Most humid weather so far this year to build in during the days ahead; surging moisture levels to fuel t-storm clusters

The average of a suite of 7-day computer model rainfall estimates through next Friday and centered on Chicago has jumped to 1.80”. Such an average is the product of more than 40 individual computer-generated predictions. Those forecasts included rainfall estimates ranging from as little as 0.93” to as much as 4”.

Mid-U.S severe weather potential on the rise; Chicago area at risk, particularly Monday and Tuesday

Since 2000, May has ranked as the top tornado-producing month across the greater Chicago area—a region which includes 17 counties from southern Wisconsin to northern Illinois and northern Indiana.

Of the 78 twisters which have been logged since the start of the 21st century, 26 of them—33% have occurred in March.  That’s why it’s little surprise the area may be headed for some challenging thunderstorm clusters capable of severe weather production in the days ahead.  This is particularly true of thunderstorms predicted to “bubble-up” into a vigorous overhead spring jet stream Monday and Tuesday next week.

Waves of severe weather are predicted to sweep the Plains Saturday then extend eastward into the Midwest Sunday.

Chicago is close enough to the area of potential severe weather that any storms which develop later Sunday into Sunday night will have to be monitored.  But, it’s the Monday, Tuesday and possibly Wednesday periods which appear likely to warrant the greatest attention.