Massive Thunderstorms Hit Chicago With Hurricane-Force Winds, Worst Power Outage in History

Images (click to enlarge): Northern Illinois regional radar and mid-atmosphere wind pattern at 8 am CDT, July 11, 2011, from National Weather Service; Chicago firefighters working to rescue driver trapped by fallen tree, from Chicago Sun-Times

July 11 Update: About 350,000 remained without power in Chicago as of Tuesday morning. The peak outage estimate was revised upward to 868,000.

Original post:
A line of severe thunderstorms brought hurricane-force winds to the Chicago area Monday morning, July 11. Although no tornadoes were reported, the extremely strong straight-line winds produced widespread power outages. At the peak, over 817,000 customers were without electricity. Commonwealth Edison reported that this was the largest outage from any storm in Chicago history.

The force of the wind moving eastward across southern Lake Michigan prompted a seiche and lakeshore flood warning as water levels oscillated rapidly by over 2 feet.

Trained spotters reported wind gusts as high as 80 mph. Wind gusts of 75 mph were measured at Midway Airport and 63 mph at O'Hare. Here are some selected reports from the National Weather Service:

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1029 AM CDT MON JUL 11 2011

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0709 AM     TSTM WND GST     FRANKLIN GROVE          41.84N 89.30W 
07/11/2011  E70.00 MPH       LEE                IL   TRAINED SPOTTER 

0715 AM     TSTM WND GST     ROCKFORD                42.27N 89.06W 
07/11/2011  E80.00 MPH       WINNEBAGO          IL   TRAINED SPOTTER 

            ESTIMATED 70 TO 80 MPH WINDS ON EAST SIDE OF ROCKFORD.

0728 AM     TSTM WND GST     NW DE KALB              41.93N 88.75W 
07/11/2011  E70.00 MPH       DE KALB            IL   TRAINED SPOTTER 

0730 AM     TSTM WND GST     SYCAMORE                41.98N 88.70W 
07/11/2011  E60.00 MPH       DEKALB             IL   TRAINED SPOTTER 

0735 AM     TSTM WND GST     ELBURN                  41.89N 88.47W 
07/11/2011  M65.00 MPH       KANE               IL   TRAINED SPOTTER 

            MEASURED WITH ANEMOMETER. TREE BLOWN DOWN BEITH ROAD 1 
            MILE EAST OF RT. 47.

0740 AM     TSTM WND GST     CRYSTAL LAKE            42.23N 88.33W 
07/11/2011  E75.00 MPH       MCHENRY            IL   TRAINED SPOTTER 

            GREATER THAN 70 MPH WINDS FOR 2 TO 3 MINUTES. POWER 
            OUTAGES. 1 FT DIAMETER TREES AND LARGE BRANCHES DOWN.

0740 AM     TSTM WND GST     ROCKFORD                42.27N 89.06W 
07/11/2011  E80.00 MPH       WINNEBAGO          IL   PUBLIC          

            70 TO 80 MPH WINDS TRANSFORMERS DAMAGED CAUSING POWER 
            OUTAGE AND SEMI BLOWN ON SIDE.

0743 AM     TSTM WND GST     SUGAR GROVE             41.77N 88.46W 
07/11/2011  M60.00 MPH       KANE               IL   ASOS            

            MEASURED AT AURORA AIRPORT.

0750 AM     TSTM WND GST     WARRENVILLE             41.82N 88.19W 
07/11/2011  E70.00 MPH       DUPAGE             IL   TRAINED SPOTTER 

            60 TO 70 MPH GUSTS AND HEAVY RAIN.

0750 AM     TSTM WND GST     SUGAR GROVE             41.77N 88.46W 
07/11/2011  M64.00 MPH       KANE               IL   ASOS            

            MEASURED AT AURORA AIRPORT.

0752 AM     TSTM WND GST     AURORA                  41.77N 88.29W 
07/11/2011  E70.00 MPH       KANE               IL   TRAINED SPOTTER 

0754 AM     TSTM WND GST     MUNDELEIN               42.27N 88.00W 
07/11/2011  M72.00 MPH       LAKE               IL   TRAINED SPOTTER 

0759 AM     TSTM WND GST     NAPERVILLE              41.76N 88.15W 
07/11/2011  E65.00 MPH       DUPAGE             IL   TRAINED SPOTTER 

            TREES BLOWN OVER.

0801 AM     TSTM WND GST     LIBERTYVILLE            42.28N 87.97W 
07/11/2011  M70.00 MPH       LAKE               IL   TRAINED SPOTTER 

0804 AM     TSTM WND GST     OHARE AIRPORT           41.98N 87.90W 
07/11/2011  M63.00 MPH       COOK               IL   ASOS            

0810 AM     TSTM WND GST     MELROSE PARK            41.90N 87.86W 
07/11/2011  E60.00 MPH       COOK               IL   TRAINED SPOTTER 

0812 AM     TSTM WND GST     3 SW MIDWAY AIRPORT     41.75N 87.79W 
07/11/2011  M75.00 MPH       COOK               IL   CO-OP OBSERVER  

0814 AM     TSTM WND GST     MIDWAY AIRPORT          41.78N 87.75W 
07/11/2011  M75.00 MPH       COOK               IL   ASOS           

0819 AM     TSTM WND GST     EVERGREEN PARK          41.72N 87.70W 
07/11/2011  M72.00 MPH       COOK               IL   TRAINED SPOTTER 

0901 AM     TSTM WND GST     GURNEE                  42.38N 87.94W 
07/11/2011  E70.00 MPH       LAKE               IL   TRAINED SPOTTER 

            15 INCH TREE UPROOTED.