The cluster of thunderstorms which moved across northern Illinois and northwest Indiana on Monday can be described as what is commonly referred to as a mesoscale convective system (MCS).
This is generally a continuous line of thunderstorms spanning many miles, over a long duration, and during which, will affect many locations.
This is a meteorological phenomenon that is not uncommon for northern Illinois and northwest Indiana during this time of the year. The weather pattern is such that, the upper level winds orient themselves in a northwest flow pattern. This orientation of the upper level winds allows waves of energy (upper level disturbances) to traverse across the region. This, coinciding with very warm, moist, and unstable conditions can trigger thunderstorm development which can lead to a complex of thunderstorms similar to what occurred on Monday. As this weather pattern persists, multiple waves of energy can move across the region providing several rounds of MCS’s for the region.
The NWS conducted storm surveys on Tuesday to assess the damage which occurred with the MCS that moved across the area on Monday. This was needed in order to validate any possible tornadoes either indicated by radar or by reports sent in via the spotter network. Any tornado confirmed by the NWS, gets a rating based on damage from that tornado. This rating is based off of the Enhanced-Fujita scale. Included with the rating, are the length and width of the path of the tornado. This information is used by the NWS for agency use, but it is also used to progress the science. Storm surveys used in conjunction with case studies can be a valuable tool to provide knowledge and insight to what occurred. Doing this, allows meteorologists to better understand storm scale features that can lead to a significant event similar to Mondays. Thus, providing a better service to the public and meteorological community.
The Chicago Weather Forecast Office would like to extend great thanks for all who helped with this event. This includes: trained spotters, emergency managers, the media, law enforcement, and amateur radio network.
Image displaying preliminary storm reports for portions of Northern Illinois and northwest Indiana. Multiple high wind damage reports were observed across much of the area, which is indicated by the blue W's. A few reports of tornadoes and funnel clouds were also called into the Weather Service, which is indicated by the red T's. A full list of the preliminary local storm reports can be accessed through the NWS website (weather.gov/chicago).
Radar image at 745 PM of the Mesocale Convective System which was in its mature bow echo stage as it moved through Cook, Dupage, and Will counties. Worthy to note are the circular looking portions north and south of the bowing segment. These are referred to as bookend vortices, which can enhance the rear inflow jet creating stronger winds at the surface.
Radar Image at 758 PM displaying the very strong winds associated with the Bow Echo. Cool colors (green) represent inbound winds toward the radar and hot colors (red) represent winds away from the radar. Worthy to note are the dark blue and purple colors in Kane county. Radar indicated possible winds near 90 MPH across this location at this time.
Bloomingdale, IL. ------------------------------------------------------------
Radar image at 745 PM displaying storm relative motion. In this image, rotation is observed near Bloomingdale, IL. This is observed through the green colors representing strong velocities directed toward the radar while the adjacent brighter red colors representing velocities away from the radar. This couplet suggests a cyclonic, or counter-clockwise circulation.
A broad area of straight line wind damage occurred across northern DuPage County with a concentrated area of stronger winds produced by what meteorologists refer to as a mesovortex. The mesovortex is apparent in the Doppler radar velocity images as a inbound-outbound couplet, indicated by the small area of bright greens immediately next to a small area of bright reds. This mesovortex persisted along the north edge of the bow echo for many miles stretching all the way from Kane county near Elburn to the Chicago lakefront near Fullerton Ave. A large area of straight line wind damage was evident from north of the DuPage Airport across Bloomingdale and Addison to Bensenville.
Damage to trees and rooftops was widespread across a portion of the Bloomingdale, Glendale Heights, and Addison area where straight line winds were estimated to have been between greater than 76 mph. Embedded within this zone was evidence of a tornado touchdown in the vicinity of Gary Ave, Scott Drive, and Fox Court, with wind speeds estimated up to 110 mph and the tornado rated at EF1. Roof and structural damage occurred to an apartment complex with windows blown out. Windows were also blown out of retail establishments at the Stratford Mall, pieces of roofing material were blown off the mall, and trees in the parking lot were blown down. Apartment buildings had windows and doors blown out, portions of rooftops peeled back and shingles off, and one wall bowed out. The actual path length and width of this tornado will be finalized by Tuesday morning.
Tornado rated EF1 (Time - 745PM)
Bolingbrook, IL. --------------------------------------------------------------
Radar image at 741 PM displaying storm relative motion. In this image, rotation is observed just west of Bolingbrook, IL. This is observed through the green colors representing strong velocities directed toward the radar while the adjacent brighter red colors representing velocities away from the radar. This couplet suggests a cyclonic, or counter-clockwise circulation.
A segment of the bow shaped line of storms moved through Naperville and Bolingbrook. This part of the storm produced a path of wind damage and a brief tornado. Starting near Plainfield-Naperville Road and Boughton Road on the west side of Bolingbrook, there were scattered tree limbs down.
The tornado apparently developed about 1/2 mile east of Plainfield-Naperville Road and about a block south of Boughton Road. There was a narrow path of more intense damage in a subdivision where several homes had sections of roofing torn off, siding and soffits torn loose, trees snapped, and limbs down. The most intense damage was on Sparrow Lane, Maroon Bells Lane, and Silverado Street.
The tornado was rated EF1 at this point with winds 86 to 110 mph. Here one house will likely be a total loss due to structural damage to the roof, covered porch, garage, and one wall. A garage was destroyed at another home. There was evidence of rotation and uplift in this area. The tornado weakened to EFO east of this area from Kings Road to Indian Chase Meadows. Winds were estimated at 65 to 85 mph. There was sporadic damage to trees and limbs, and a few homes had damage to shingles, siding, and soffits. A small section of roof was removed from a house just east of Indiana Chase Meadows. At this point the tornado apparently dissipated but strong straight-line winds fanned out.
The damage path widened to 1/4 to 1/2 mile wide just south of Clow Airport and between Weber Road and Veterans Parkway, just south of Lilly Cache Lane. Fences were blown down and sporadic minor tree damage continued. In an older subdivision with larger more mature trees, there were a lot of limbs down and a few trees snapped or uprooted. But the houses were more sheltered by the big trees and there was very little damage to homes in this area. The strong winds continued east of Veterans Parkway. Small limbs were down at Jane Adams School. From the school east southeast to Schmidt Road, a few homes had siding peeled back, or soffit damaged.
There was sporadic damage to small trees, and loose objects such as trampolines, portable basketball sets, were blown over. Winds were likely 60 to 75 mph in this area. East of Schmidt Road, along Remington Road and the Frontage Road, damage to tree limbs was very minor. A construction trailer on the Frontage Road, east of Woodcreek Drive was destroyed. Winds were estimated to be 85 to 95 mph at this point. South of I-55, a large metal hotel sign was broken and a wooden pole holding a tornado siren was snapped. There was damage to an air conditioning unit on the roof of an industrial building. There was minor damage to trees along Old Chicago Road, east of Route 53 to Joliet Road. Large trees were damaged on Joliet Road. East along Bluff Road from Joliet Road to near I-355, only sporadic minor damage to tree limbs was found with winds around 50 to 60 mph.
The tornado was rated EF1 (Time - 745) with a damage path 1.1 miles long and 50 yards wide.
Griffith, IN ----------------------------------------------------------------------
Radar image at 828 PM displaying storm relative motion. In this image, rotation is observed in northern Lake county near Griffith, Indiana. This is once again observed through the green colors representing strong velocities directed toward the radar while the adjacent brighter red colors representing velocities away from the radar. This couplet suggests a cyclonic, or counter-clockwise circulation.
Map of tornado near Griffith, IN.
Storm Survey #3 focused on the storm circulation that caused the brief Bolingbrook tornado as it tracked eastward into northwest Indiana. This circulation tightened up and strengthened as it reached far northwest Lake County just to the north of Munster. The strongest radar velocity signatures appeared as the storm passed through Griffith. It was at this point that we received reports of funnel clouds and measured 80 mph winds and wide spread damage across the city.
The damage path continued eastward for approximately a total of 5 miles along and north of Ridge Rd until the damage appeared to become less around Chase Rd and Ridge Rd. Scattered 1 to 3 inch tree branches were still noted to be down further east from here, but this was likely more so due to the line of storms rolling through.
Tornado rated EF2 (Time - 828 PM) with a damage path 5 miles long and 30 yards wide.
Boswell, IN -------------------------------------------------------------------------------------
1. Tornado destroys homes
Published: 04:00 AM Aug 5,2008
2. Path of destruction
Published: 04:00 AM Aug 6,2008
The tornado that slammed into Griffith Monday was rated an EF2, the strongest in more than a decade, according to the National Weather Service.
3. Quickly for Porter County Neighbors 4/20
Published: 04:00 AM Apr 20,2007
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4. NIPSCO still working to restore power
Published: 04:00 AM Aug 6,2008
Thousands of NIPSCO customers in Lake and Porter counties remain without power as crews continue to reconnect those affected by Monday's tornado and severe storms. Porter County power is expected to be fully restored today, while many Lake County homes may have to wait till Thursday, NIPSCO said. Watch the Post-Tribune for continuing storm coverage.
5. Power outages expected through Saturday
Published: 12:00 AM Aug 7,2008
Twenty thousand Northwest Indiana residents and businesses remained without power late Wednesday, two days after a tornado and severe thunderstorms slammed the region, snapping trees, destroying homes and leaving one motorist dead. Most of the outages ...
6. Conditions perfect for microbursts, expert says
Published: 12:00 AM Aug 7,2008
VALPARAISO -- Northwest Indiana's resident tornado expert was vacationing in sunny Wisconsin when a twister struck the region this week. Valparaiso University meteorology professor Bart Wolf said he watched with a mixture of awe and envy as storm tower...
Fifth Tornado from Monday Confirmed - Orland Park
The type of damage observed in Orland Park was first classified by Dr. Ted Fujita (same researcher who invented the F scale for tornado classification – now used as the EF [Enhanced Fujita] scale) as a wide-end tornado while he worked at the University of Chicago during the 1970s. A wide end tornado by definition includes both tornado and downburst. It is believed that a strong downburst behind the weakening tornado undercuts the tornado circulation, in effect wiping out the swirling motion. This scenario is consistent with what eyewitnesses in the area observed on the evening of the 4th.
Tornado rated EF0 (Time - 800 PM CDT) with a path 0.25 miles long and 30 yards wide.
Try and have a better weekend!