Storm Environment

August 4th, 2008 Chicago Derecho Tim Halbach – NWS Chicago Ron Przybylinski – NWS St. Louis Advanced Spotter Training-March 14, 2009 Event Overview yyProgressive Derecho developed in eastern Iowa/northwest Illinois and caused widespread damage and power outages across northern Illinois and Indiana yDissipated over West Virginia Worst damage occurred north of the apex of the bow where multiple mesovorticies developed yWell developed convective system featuring a long lived Book-End Vortex and Rear Inflow Jet yStrong winds persisted well after the leading edge of the derecho •very low RIJ? y6 tornadoes were confirmed via storm surveys yyyyyGriffith, IN: EF2 Bloomingdale, IL: EF1 (2 Tornadoes) Bolingbrook, IL: EF1 Orland Park, IL: EF0 Boswell, IN: EF0 Storm Environment 250 MB 3pm CDT Surface Map Forecast NAM Bufr Soundings- 21z at ORD Severe Thunderstorm Watches Nested Storm Based Warning Sectorization y Used a nested storm based warning sectorization for this event y 2 Meteorologists issuing severe warnings y 1 Meteorologist issuing tornado warnings Radar Analysis of the 5 Main Rotations The 5 Rotations Mesovort #1 y Developed along the Ogle/Carroll County line y Strengthened near Mount Morris • straight-line wind damage w/no tornado y Grain bin blown down, phone tower knocked over, building leveled. y Rotation lasted for about 1 hour and traveled about 60 miles from Carroll County into northern De Kalb county The 5 Rotations The 5 Rotations The 5 Rotations Mesovort #1 Mesovort #1 Mesovort #1 y Strongest rotation near Mount Morris The 5 Rotations Mesovort #1 Mesovort #1 Mesovort #2 y 108.8 knots sampled at 5130ft Above Ground Level The 5 Rotations -Damage Pictures from Ogle County The 5 Rotations y Developed further to the south across north central De Kalb county. y A funnel cloud was reported NE of Hampshire, y Main damage reports being from large trees being knocked down. y Rotation lasted for about 30 minutes and 25 miles from north central De Kalb county northeast into north central Kane county The 5 Rotations The 5 Rotations The 5 Rotations Mesovort #2 Mesovort #2 Mesovort #2 y Strongest rotation for #2 east of Hampshire The 5 Rotations Mesovort #3 y Developed over central Kane county y The first confirmed tornado occurred with this rotation y The worst damage occurred in Bloomingdale where a survey confirmed that two EF1 Tornadoes occurred. y Industrial building collapse, y Damage to Stratford Square Mall y Rotation lasted for about 40 minutes and 30 miles from north of Elburn in central Kane County eastward through central DuPage county to just NW of Franklin Park in Cook County The 5 Rotations Mesovort #3 The 5 Rotations Mesovort #3 The 5 Rotations Mesovort #3 Mesovort #3 Mesovort #4 y Strongest rotation near Bloomingdale The 5 Rotations -Pictures from DuPage County near Bloomingdale The 5 Rotations y Developed in central DuPage County y A tornado was reported near Elmhurst y Tracked through north side of Chicago • Cubs/Astros game was in progress (eventually cancelled) y The main damage from this rotation was major tree damage and power outages y The rotation was tracked for about 30 minutes and 25 miles from near Glen Ellyn, eastward along I-290 where it veered northeast near Oak Park and tracked through Lincoln Park. y The Harrison Crib marine observation recorded a 94mph wind out over the lake. The 5 Rotations The 5 Rotations The 5 Rotations Mesovort #4 Mesovort #4 Mesovort #4 y Strongest rotation as it tracked through the north side of Chicago The 5 Rotations Mesovort #4 y 63.0 knots sampled at 1856ft Above Ground Level The 5 Rotations Mesovort #4 y Hook echo east of Hillside y ORD Terminal Doppler Radar The 5 Rotations Spin Up #4 The 5 Rotations Mesovort #5 y Developed over northern Will County y Strongest of all the rotations • produced the most tornadoes and worst damage • fed off of an earlier lake breeze which stalled out where the rotation tracked through y Three tornadoes were confirmed via surveys in Bolingbrook (EF1), Orland Park (EF0), and Griffith (EF2). y Tracked for almost 3 hours and about 150 miles from northern Will County to just southwest of Fort Wayne, Indiana The 5 Rotations Mesovort #5 The 5 Rotations Mesovort #5 The 5 Rotations The 5 Rotations Mesovort #5 y 1st Tornado: west side of Bolingbrook y Rated an EF1 tornado y The main damage was to house roofs and tree damage y 1.1 mile long and 50 yards wide The 5 Rotations Mesovort #5 The 5 Rotations Mesovort #5 y 2nd Tornado: north side of Orland Park y Rated a brief EF0 tornado y Numerous trees knocked down, a fence was blown down, a gazebo was thrown 30ft and the roof to an auto shop was damaged y 0.25 miles long and about 30 yards wide The 5 Rotations Mesovort #5 Orland Park EF0 Tornado The 5 Rotations Mesovort #5 y 3rd Tornado: Griffith, Indiana along Ridge Rd Rated an EF2 tornado yy Griffith Park Plaza Mall had windows blown out and a portion of a roof was blown off/down. y Subdivision east of mall had multiple homes with substantial damage including entire roofs blown off and a garage collapse. y Habitat for Humanity storage facility was a complete loss y 5 miles long and 30 yards wide The 5 Rotations Other Info y Another tornado occurred with a separate storm in Benton County after the derecho came through y Rated EF0 southeast of Boswell y A band of marginally severe storms reformed over Cook County after the bow came through y Another line of severe storms came through later in the morning which caused damage in Kankakee and Iroquois Counties y Flooding was an issue across the Chicago Metro area y No major injuries or deaths in LOT County Warning Area Lightning y From 4pm CDT through 10pm CDT…31,559 cloud to ground lightning strikes were registered across the region. y 5,260 per hour, 88 per minute, 1.5 per second y 1736 positive strikes • Positive strikes are much more dangerous than negative strikes. Originate at the top of storms and require a stronger electric field to reach the ground (10x Amps compared to negative strikes) and last longer. The 8pm to 9pm period had the most strikes: 13,113 in an hour 219 per minute 3.5 per second Lightning (cont) Summary y Long lived derecho that caused considerable damage across northern Illinois/Indiana y Nested Warning Sectorization y 6 total Tornadoes surveyed y Hardest hit areas were along the paths of the 5 rotations/mesovorticies y Strongest rotation was with the northwest Indiana mesovort that was likely strengthened by lake breeze boundary y Lightning strikes were impressive with more than one per second over a 6 hour period

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