A few gusty thunderstorms may yet develop across the Chicago area this afternoon, but the threat of any organized severe weather remains very low. The Storm Prediction Center has removed Chicago from the "Slight Risk" categorization.
The greatest threat of severe storm development today is expected to be in the southern plains with northeastern Texas, northwest Louisiana, the southeast tip of Oklahoma and southwestern Arkansas under a moderate risk of severe storms (see red-shaded area on map below).
A good portion of Lower Michigan, Indiana and southern and eastern Illinois have been placed in the slight risk area today with the immediate Chicago area and south on the western edge of the outlined area (yellow-shaded area on map below). With normal daytime heating showers and thunderstorms may develop primarily this afternoon and evening with strongest storms likely east of a line from Pontiac, Illinois to Gary, Indiana.
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.
My wife and I just returned from our winter home in Gilbert, Arizona. One day the humidity was 1 percent. What’s Chicago’s lowest humidity? And the world’s?
--Bob Hansen, Lindenhurst
Chicago climatologist Frank Wachowski reports that the city’s all-time low relative humidity is 13 percent, recorded on three occasions. It first occurred during a dust storm on May 10, 1934, and was tied on April 11, 1956, and April 8, 1971. Chicago’s low humidity episodes generally occur on warm, windy afternoons when dry air aloft can easily mix down to the surface. For the record, one of the world’s lowest humidities was recorded Oct. 24, 2006, in Coober Pedy, Australia, when a temperature of 93 and a dew point of minus 23 produced a relative humidity of less than 1 percent.
For the latest information on this evening's severe thunderstorm watch please link to the Chicago Weather Center Severe Weather Blog
A severe thunderstorm watch will be in effect for much of the Chicago area until 3am CDT for much of the Chicago area.
The following Illinois counties are included in the severe thunderstorm watch..
IN ILLINOIS THIS WATCH INCLUDES 18 COUNTIES IN NORTH CENTRAL ILLINOIS BOONE DE KALB LA SALLE LEE OGLE WINNEBAGO IN NORTHEAST ILLINOIS COOK DUPAGE GRUNDY KANE KANKAKEE KENDALL LAKE IL MCHENRY WILL
IN CENTRAL ILLINOIS LIVINGSTON IN EAST CENTRAL ILLINOIS FORD IROQUOIS
THIS INCLUDES THE CITIES OF...AURORA...BELVIDERE...CHICAGO... DEKALB...DIXON...JOLIET...KANKAKEE...MORRIS...OREGON...OSWEGO... OTTAWA...PIPER CITY...PONTIAC...ROCKFORD...WATSEKA...WAUKEGAN... WHEATON AND WOODSTOCK.
Strong to severe thunderstorms are spreading northeast from west central Illinpis. Severe thunderstorm warnings valid until 8:15 pm have just been issued for portions of central Illinois including the Peoria area. Wind gusts of 60 mph or higher and hail as large as ping-pong balls can be expected. These storms are on a northeast track and headed towards the Chicago Metro area later this evening.
The latest timescale discussion #736 from the Storm Prediction Center indicates a tornado or severe thunderstorm watch might be issued later this evening.
MESOSCALE DISCUSSION 0736 NWS STORM PREDICTION CENTER NORMAN OK 0717 PM CDT MON MAY 20 2013 AREAS AFFECTED...CNTRL INTO NRN IL CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE VALID 210017Z - 210115Z PROBABILITY OF WATCH ISSUANCE...60 PERCENT SUMMARY...THE THREAT FOR SEVERE STORMS CAPABLE OF DAMAGING WINDS...LARGE HAIL...AND PERHAPS A TORNADO IS EXPECTED TO DEVELOP NEWD ACROSS THE AREA THIS EVENING INTO TONIGHT. CONVECTIVE TRENDS ARE BEING MONITORED FOR A POSSIBLE WW. DISCUSSION...RECENT TRENDS IN REGIONAL RADAR DATA INDICATE TSTMS DEVELOPING E OF THE MS RIVER /NW OF SPI/ IN ADVANCE OF AN EVOLVING QLCS OVER MO. VISIBLE SATELLITE IMAGERY AND SURFACE OBSERVATIONS SUGGEST THAT THE ERN-MOST STORMS ARE FORMING NEAR AN OUTFLOW BOUNDARY LIFTING NWD THROUGH CNTRL IL. THE 00Z ILX APPEARS TO BE A REASONABLE PROXY FOR THE ENVIRONMENT S OF THE OUTFLOW BOUNDARY WHERE STEEP LAPSE RATES AND A MOIST PBL /LOWEST 100-MB MEAN-MIXING RATIOS OF AROUND 13 G PER KG/ WERE YIELDING A MODERATELY UNSTABLE ENVIRONMENT. WHEN COUPLED WITH A VERTICALLY VEERING WIND PROFILE WITH 40-50 KT SWLY MIDLEVEL WINDS...THE ENVIRONMENT APPEARS SUPPORTIVE OF ORGANIZED STORM MODES...INCLUDING SUPERCELLS AND BOWING STRUCTURES WITH A RISK FOR DAMAGING WINDS...LARGE HAIL...AND PERHAPS A TORNADO.