Transcript 41821
EF3 TORNADO WITH A ½ TO 3/4 MILE-WIDE PATH DEVASTATES MAPLETON, IOWA ADVANCE WARNING SAVED LIVES 7:20 PM, SATURDAY APRIL 9, 2011 Walter Hays, Global Alliance for Disaster Reduction, University of North Carolina, USA TEN TORNADOES • The National Weather Service confirmed that 10 tornadoes hit Iowa over the weekend of April 9-10. ADVANCE WARNING • The advance warning system sirens sounded in Mapleton at 7:05 p.m., allowing residents 15 minutes to take cover. THE PEOPLE RESPONDED • They huddled in basements and bathrooms and hid beneath furniture or stairwells as winds up to 140 mph sucked, twisted and damaged buildings, homes and vehicles across Mapleton. 60 % OF MAPLETON, IA DESTROYED, BUT … One of the 10 twisters destroyed or damaged more than 100 homes and injured more than a dozen people. BUT NO DEATHS, DUE IN PART TO 15 MINUTES OF ADVANCE WARNING DAMAGE IN MAPLETON BACKGROUND TORNADOE SEASON • The peak tornado season is late winter through midsummer,…. • But tornadoes can happen any time of the year when the atmospheric conditions are right. TORNADO ALLEY • ALTHOUGH TORNADOES HAVE OCCURRED IN EVERY STATE, THEY OCCUR MOST FREQUENTLY IN “TORNADO ALLEY,” WHICH INCLUDES PARTS OF: TEXAS, OKLAHOMA, ARKANSAS, TENNESSEE, NEBRASKA, KANSAS, MISSOURI, ILLINOIS, AND IOWA. PHYSICS OF A TORNADO THE PHYSICS OF TORNADOES • TORNADOES ARE CAUSED BY THE COLLISION OF DESCENDING COLD AIR MASSESS COMING FROM THE NORTH AND ASCENDING WARM AIR MASSES COMING FROM THE SOUTH. THE PHYSICS OF TORNADOES • THE COLLISION CREATES A FUNNEL OF HIGH-VELOCITY WIND THAT IS VERY DESTRUCTIVE AS IT “TOUCHES DOWN” ONE OR MORE TIMES ALONG A LONG, NARROW (TYPICALLY 10-100 M) PATH. HAZARDS OF A TORNADO (AKA POTENTIAL DISASTER AGENTS) • WIND: SPEEDS CAN REACH 500 KM/HR (300 MI/HR) • THUNDER, LIGHTNING, AND HEAVY PRECIPITATION E EXTREME • HAIL CAN BE VERY DAMAGING ILLUSTRATIVE PHOTOS OF SOME PAST TORNADOES “TOUDHDOWN” –IOWA IN 2008 PHOTO OF A “TOUCHDOWN” PJOTO OF A “TOUCHDOWN” PJOTO OF A “TOUCHDOWN”