A strong thunderstorm complex moved through east central Iowa and northern Illinois early Monday morning, July 11th. Damaging winds exceeded 100 mph at times and uprooted large trees, downed power lines, and ripped roofs off of buildings. Portions of northern Tama, northern Benton, and northwestern Linn County were hardest hit. National Weather Service storm survey teams assessed damage and estimated wind speeds in the 110 to 130 mph range in these hardest hit areas.
Details for some of the local communities follow:
Garrison Iowa: straight line wind of 110 to 130 mph produced widespread damage to structures. Many roofs were partially or fully removed and the walls of some buildings collapsed, including the fire station and town library. Nearly every tree was significantly damaged or snapped off . Power outages were widespread.
Between Garrison and Vinton, 2 pairs of steel electrical transmission towers were bent over. Several farms received devastating damage, including a house that lost its roof and most exterior walls and another that lost nearly every grain bin and outbuilding.
At Vinton, Iowa: straight line wind in excess of 110 mph caused damage to numerous roof structures and some exterior walls, including a downtown apartment building. Nearly every tree was significantly damaged or snapped off.
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|Garrison, IA Fire Department||Garrison, IA Public Library||Metal power transmission poles bent over. Flattened corn in foreground. Between Garrison and Vinton.|
|Devastated farm between Garrison and Vinton||Hwy 218 on west side of Vinton. Several large power poles down.||Iowa Braille School. Vinton, IA|
|Trees and power lines down on cars and homes in Vinton, IA||Vinton, IA Public Library lost all trees and some windows.||View down 5th Street in Vinton from intersection of 5th and 2nd.|
|Local Storm Reports Map - Click on Map for interactive display.
||National Storm Reports Map
Radar loop courtesy Iowa Environmental Mesonet.
This thunderstorm complex fits the description of a bow echo "derecho" which is a widespread, long-lived windstorm that is associated with a band of rapidly moving showers or thunderstorms. The term bow echo refers to the arched, bow-like structure of the thunderstorm complex seen in the radar reflectivity data above. The same thunderstorm complex that produced widespread wind damage in the Central Plains and Midwest actually persisted all the way to the Mid Atlantic, producing a swath of nearly continuous wind damage of varying magnitude.
The Evolution: The storm first took shape as a cluster of low end severe storms over southern Nebraska during the late afternoon of July 10. The system continued northeastward and entered western Iowa after midnight, still as a line of marginally severe storms. As the system passed through the northern Des Moines metro area around 3:30am, it interacted with an outflow boundary from the storms to the north and rapidly intensified as it accelerated eastward. Over the next hour and a half the storm plowed eastward through Story, Marshall, and Tama Counties, blasting the area with winds of up to 105 mph, the equivalent of an EF1 tornado. The storm continued to track eastward, intensifying further as it plowed through Benton and Linn Counties with peak winds estimated at 110 to 130 mph. The storm then began to weaken but remained severe as it continued eastward into northern Illinois and the southern Great Lakes region before dissipating in Maryland mid-afternoon. Thousands of trees were downed in eastern Iowa alone and numerous structures were damaged or destroyed.
The Environment: Derechos are able to last for several hours, and their gust fronts produce high end damage. In order for these storms to last so long, they need both instability and wind shear. Instability refers to the storm's ability to tap into the warm moist air near the surface as it develops. Meteorologists use the term CAPE (Convective Available Potential Energy) as a way to measure the amount of instability. Wind shear refers to how the wind changes at different heights above ground. Generally, severe weather is likely when the atmosphere has a combination of both high instability and high shear values. In this case, there was plenty of warm moist air at the surface. Temperatures as of 2AM were near 80F across Central Iowa, and dew points were in the mid 70s. This contributed to high CAPE values of near 5000 J/kg. At the same time, the wind shear in the lowest 3000 ft of the atmosphere was near 30 kts, which is quite high.
PRELIMINARY LOCAL STORM REPORT...SUMMARY NATIONAL WEATHER SERVICE QUAD CITIES IA IL 1012 AM CDT MON JUL 11 2011 ..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON... ..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE.... ..REMARKS.. 0438 AM TSTM WND GST BELLE PLAINE 41.90N 92.27W 07/11/2011 E55.00 MPH BENTON IA EMERGENCY MNGR ESTIMATED 50 TO 55 MPH WINDS 0449 AM TSTM WND GST 3 SE KEYSTONE 41.97N 92.15W 07/11/2011 M75.00 MPH BENTON IA TRAINED SPOTTER 0450 AM TSTM WND DMG BELLE PLAINE 41.90N 92.27W 07/11/2011 BENTON IA TRAINED SPOTTER LARGE TREES DOWN IN TOWN WITH POWER OUTAGES REPORTED ON NORTH SIDE. 0450 AM TSTM WND GST BELLE PLAINE 41.90N 92.27W 07/11/2011 E60.00 MPH BENTON IA TRAINED SPOTTER 0458 AM TSTM WND GST VINTON 42.16N 92.03W 07/11/2011 E65.00 MPH BENTON IA EMERGENCY MNGR REPORTED BY BENTON EOC. 0500 AM TSTM WND GST VINTON 42.16N 92.03W 07/11/2011 M70.00 MPH BENTON IA EMERGENCY MNGR 70+ MPH WINDS BEING SEEN AT THIS TIME. 0501 AM TSTM WND DMG 2 N VINTON 42.19N 92.03W 07/11/2011 BENTON IA EMERGENCY MNGR SEMI BLOWN OFF HIGHWAY 150 JUST NORTH OF TOWN. 0503 AM TSTM WND DMG KEYSTONE 42.00N 92.20W 07/11/2011 BENTON IA TRAINED SPOTTER NUMEROUS 12 TO 14 INCH TREES DOWN IN TOWN...CROP DAMAGE IS ALSO BEING SEEN. TIME ESTIMATED FROM RADAR. 0505 AM TSTM WND DMG W VINTON 42.16N 92.03W 07/11/2011 BENTON IA TRAINED SPOTTER 2X4 FLEW THROUGH EXTERIOR WALL OF HOME...KNOCKING TV OVER INSIDE HOME...TIME ESTIMATED FROM RADAR. 0505 AM TSTM WND GST 1 SSE CEDAR RAPIDS 41.95N 91.66W 07/11/2011 E60.00 MPH LINN IA TRAINED SPOTTER 0506 AM TSTM WND GST CEDAR RAPIDS MUNICIPAL 41.88N 91.72W 07/11/2011 M52.00 MPH LINN IA ASOS 0509 AM TSTM WND GST 1 NW MARION 42.05N 91.61W 07/11/2011 E60.00 MPH LINN IA TRAINED SPOTTER ESTIMATED 55 TO 60 MPH. 0510 AM TSTM WND DMG 2 S CENTER POINT 42.16N 91.78W 07/11/2011 LINN IA TRAINED SPOTTER 3 TREES BLOWN OVER LEWIS ACCESS ROAD BLOCKING ROAD TO BRIDGE ACROSS CEDAR RIVER. TIME ESTIMATED. 0510 AM TSTM WND DMG CENTER POINT 42.19N 91.78W 07/11/2011 LINN IA TRAINED SPOTTER LARGE NUMBER OF 12 TO 16 INCH TREES DOWN IN TOWN...DELAYED REPORT. TIME ESTIMATED. 0511 AM TSTM WND GST 1 SSE CEDAR RAPIDS 41.95N 91.66W 07/11/2011 E80.00 MPH LINN IA TRAINED SPOTTER 0512 AM TSTM WND GST VINTON 42.16N 92.03W 07/11/2011 M60.00 MPH BENTON IA EMERGENCY MNGR SINCE 5 AM HAVE HAD SUSTAINED 60 MPH WINDS...REPORTED BY COUNTY EOC. 0512 AM TSTM WND GST 3 E CEDAR RAPIDS 41.97N 91.61W 07/11/2011 E70.00 MPH LINN IA TRAINED SPOTTER 0514 AM TSTM WND DMG URBANA 42.22N 91.88W 07/11/2011 BENTON IA TRAINED SPOTTER INTERSTATE SIGNS BLOWN OVER NEAR SUNSET ST EXIT ON I-380...MANY 4 INCH DIAMETER TREES SNAPPED OFF...TIME ESTIMATED FROM RADAR. 0515 AM TSTM WND GST 1 NW SHELLSBURG 42.10N 91.88W 07/11/2011 E80.00 MPH BENTON IA TRAINED SPOTTER TIME ESTIMATED FROM RADAR. 0516 AM TSTM WND DMG URBANA 42.22N 91.88W 07/11/2011 BENTON IA TRAINED SPOTTER 8 SMALL UTILITY SIZE TRAILERS BLOWN OVER ON I-380...LOTS OF FLATTENED CROP DAMAGE IN THE AREA SEEN AS WELL...TIME ESTIMATED FROM RADAR. 0520 AM TSTM WND DMG CENTER POINT 42.19N 91.78W 07/11/2011 LINN IA TRAINED SPOTTER LAZY ACRES CAMPGROUND...CAMPER FLIPPED OVER...TIME ESTIMATED FROM RADAR. 0521 AM TSTM WND DMG SHELLSBURG 42.09N 91.87W 07/11/2011 BENTON IA EMERGENCY MNGR METAL BUILDING COMPLETELY DESTROYED WITH NUMEROUS ROOFS BLOWN OVER IN TOWN. 0523 AM TSTM WND GST TODDVILLE 42.10N 91.72W 07/11/2011 M72.00 MPH LINN IA EMERGENCY MNGR TIME ESTIMATED FROM RADAR. 0524 AM TSTM WND DMG CENTER POINT 42.19N 91.78W 07/11/2011 LINN IA FIRE DEPT/RESCUE SEMI OVERTURNED AT CENTER POINT I-380 TRUCK STOP. 0524 AM TSTM WND GST CENTER POINT 42.19N 91.78W 07/11/2011 E60.00 MPH LINN IA FIRE DEPT/RESCUE 60+ MPH WINDS...RELAYED BY EMERGENCY MANAGER. 0524 AM TSTM WND GST PALO 42.06N 91.80W 07/11/2011 E70.00 MPH LINN IA FIRE DEPT/RESCUE TIME ESTIMATED FROM RADAR...RELAYED BY EMERGENCY MANAGER. 0525 AM TSTM WND DMG TODDVILLE 42.10N 91.72W 07/11/2011 LINN IA EMERGENCY MNGR NUMEROUS POWER OUTAGES REPORTED IN TOWN AS WELL AS IN ALBURNETT. 0528 AM TSTM WND DMG ANAMOSA 42.11N 91.28W 07/11/2011 JONES IA EMERGENCY MNGR COUNTY EMA REPORTS TREES DOWN COUNTYWIDE. OCCURRED BETWEEN ABOUT 520 AM AND 610 AM. 0530 AM TSTM WND DMG WALKER 42.29N 91.78W 07/11/2011 LINN IA FIRE DEPT/RESCUE NUMEROUS TREES BLOWN OVER WITH SOME CARS DAMAGED. 0530 AM TSTM WND DMG PALO 42.06N 91.80W 07/11/2011 LINN IA TRAINED SPOTTER 3 FOOT DIAMETER TREE BLOWN DOWN. DELAYED REPORT RELAYED BY DES MOINES NWS OFFICE. 0535 AM TSTM WND GST MONTICELLO MUNICIPAL AI 42.23N 91.17W 07/11/2011 M66.00 MPH JONES IA AWOS 0537 AM TSTM WND DMG S MANCHESTER 42.49N 91.46W 07/11/2011 DELAWARE IA EMERGENCY MNGR WINDOWS BROKEN IN SOME HOMES...WITH SOME POWER OUTAGES BEING REPORTED AS WELL. 0550 AM TSTM WND DMG 4 WNW DUBUQUE 42.52N 90.76W 07/11/2011 DUBUQUE IA TRAINED SPOTTER ASBURY AREA. 24 INCH DIAMETER TREE SPLIT IN HALF. ALSO 1.3 INCHES OF RAIN WITH STORM. 0554 AM TSTM WND DMG 3 SSW CENTER JUNCTION 42.07N 91.11W 07/11/2011 JONES IA TRAINED SPOTTER TOP HALF OF A 12 INCH DIAMETER PINE TREE SNAPPED OFF. 0554 AM TSTM WND GST 3 SSW CENTER JUNCTION 42.07N 91.11W 07/11/2011 E65.00 MPH JONES IA TRAINED SPOTTER 0555 AM TSTM WND GST DUBUQUE REGIONAL AIRPOR 42.40N 90.72W 07/11/2011 M60.00 MPH DUBUQUE IA ASOS 0600 AM TSTM WND GST CHARLOTTE 41.96N 90.47W 07/11/2011 M72.00 MPH CLINTON IA TRAINED SPOTTER 0600 AM TSTM WND DMG CHARLOTTE 41.96N 90.47W 07/11/2011 CLINTON IA TRAINED SPOTTER TWO LARGE TREES BLOWN DOWN. 0602 AM TSTM WND DMG 4 WNW DUBUQUE 42.52N 90.76W 07/11/2011 DUBUQUE IA TRAINED SPOTTER 12 INCH DIAMETER TREES DOWN ON PROPERTY ON TOP OF AN OUTBUILDING. 0607 AM TSTM WND GST DUBUQUE REGIONAL AIRPOR 42.40N 90.72W 07/11/2011 M64.00 MPH DUBUQUE IA ASOS 0610 AM TSTM WND GST DUBUQUE REGIONAL AIRPOR 42.40N 90.72W 07/11/2011 M74.00 MPH DUBUQUE IA ASOS 0610 AM TSTM WND GST 3 W BALLTOWN 42.64N 90.93W 07/11/2011 M67.00 MPH DUBUQUE IA TRAINED SPOTTER ALSO WIDESPREAD CROP DAMAGE. 0615 AM TSTM WND GST 1 N LONG GROVE 41.71N 90.58W 07/11/2011 E60.00 MPH SCOTT IA NWS EMPLOYEE DAMAGE TO SHINGLES ON HOME. 0615 AM HEAVY RAIN WSW QUASQUETON 42.40N 91.76W 07/11/2011 M1.37 INCH BUCHANAN IA COCORAHS RAIN FELL BETWEEN 5 AM AND 6 AM THIS MORNING. 0616 AM TSTM WND GST DAVENPORT MUNICIPAL AIR 41.62N 90.58W 07/11/2011 M54.00 MPH SCOTT IA ASOS 0620 AM TSTM WND DMG W APPLE RIVER 42.50N 90.10W 07/11/2011 JO DAVIESS IL TRAINED SPOTTER SEVERAL LARGE TREES BLOWN DOWN ALONG WITH METAL FLAG POLE. 0625 AM TSTM WND GST 7 NW MOUNT CARROLL 42.17N 90.07W 07/11/2011 E65.00 MPH CARROLL IL TRAINED SPOTTER 0625 AM TSTM WND DMG CLINTON 41.84N 90.23W 07/11/2011 CLINTON IA TRAINED SPOTTER POWER LINES DOWN IN TOWN. TIME ESTIMATED. 0627 AM TSTM WND DMG STOCKTON 42.35N 90.01W 07/11/2011 JO DAVIESS IL BROADCAST MEDIA STORM WINDOWS BLOWN IN. METAL YARD FURNITURE BLOWN AROUND YARD. RELAYED PUBLIC REPORT BY WREX. 0627 AM TSTM WND GST 4 WSW LORAN 42.22N 89.99W 07/11/2011 E65.00 MPH JO DAVIESS IL TRAINED SPOTTER 0628 AM TSTM WND GST DUBUQUE REGIONAL AIRPOR 42.40N 90.72W 07/11/2011 M56.00 MPH DUBUQUE IA ASOS 0630 AM TSTM WND DMG E ANDREW 42.15N 90.59W 07/11/2011 JACKSON IA TRAINED SPOTTER 1 INCH DIAMETER LIMBS DOWN IN ANDREW. 0630 AM TSTM WND DMG MAQUOKETA 42.07N 90.67W 07/11/2011 JACKSON IA TRAINED SPOTTER TREE BRANCHES DOWN BLOCKING STREETS IN MAQUOKETA. TIME ESTIMATED. POWER OUTAGE. 0635 AM TSTM WND GST 1 ESE NORA 42.46N 89.93W 07/11/2011 E70.00 MPH JO DAVIESS IL TRAINED SPOTTER 0635 AM TSTM WND DMG 1 ESE NORA 42.46N 89.93W 07/11/2011 JO DAVIESS IL TRAINED SPOTTER LARGE TREE BLOWN DOWN. 0650 AM TSTM WND GST 3 W ROCK FALLS 41.77N 89.74W 07/11/2011 E60.00 MPH WHITESIDE IL TRAINED SPOTTER TIME ESTIMATED 0653 AM TSTM WND GST ROCK FALLS 41.77N 89.69W 07/11/2011 E60.00 MPH WHITESIDE IL EMERGENCY MNGR ESTIMATED 50 TO 60 MPH WINDS...RELAYED BY ROCK FALLS ESDA. 0653 AM TSTM WND GST STERLING 41.80N 89.69W 07/11/2011 E70.00 MPH WHITESIDE IL TRAINED SPOTTER 0655 AM TSTM WND GST FREEPORT ALBERTUS AIRPO 42.25N 89.58W 07/11/2011 M57.00 MPH STEPHENSON IL AWOS