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By: Dr. Jeff Masters , 1:29 PM GMT on May 20, 2013
The Midwest U.S. is under the gun again today, as a potent storm system that spawned a preliminary count of 24 tornadoes in five states on Sunday reloads and prepares to dish out another afternoon and evening of atmospheric mayhem. Sunday's tornadoes swept through Oklahoma, Kansas, Iowa, Missouri, and Illinois, with Oklahoma bearing the brunt of the assault. The outbreak's only deadly tornado--preliminarily rated as en EF-5 with 166 - 200 mph winds--hit Shawnee, Oklahoma, a town of 30,000 located 35 miles southeast of Oklahoma City. The twister leveled a trailer park, killing two people, and blew a semi-trailer off of an expressway overpass on I-40. At least 21 people were injured and 300 homes destroyed over the five-state area by the tornadoes. The 24 tornadoes from May 19 make it the biggest day for tornadoes in the U.S. this spring, and the highest number reported in one day since January 30, when 44 tornadoes touched down from Georgia to Indiana.
Figure 1. The Shawnee, Oklahoma tornado at 6:44 pm CDT May 19, 2013, as it passed just NW of Shawnee. The tornado killed two people in a mobile home park in Shawnee. Viewer submitted photo. #okwx pic.twitter.com/UCH9e8o9G8 Matt Mahler@themahler
Figure 2. The Shawnee tornado hurled a semi-trailer off of an expressway overpass at Highway 117 and I-40 in Oklahoma, and toppled another semi. Four people who sheltered under this overpass were injured, one seriously, and taken to the hospital. Highway overpasses can act to amplify a tornado's winds, and are very dangerous places to be during a tornado. According to the NWS in Norman Oklahoma, during the tornado outbreak of May 3, 1999, tornadoes crossed three highway overpasses, and at all three locations, there was a fatality. One of the fatalities occurred from an EF-2 tornado in a rural area, which suggests that a tornado need not be a large, violent tornado with a considerable debris cloud to cause fatal injuries to people seeking shelter from storms under overpasses. In addition to the fatal injuries to three people, there were also many severe, potentially life-threatening and gruesome injuries inflicted upon people underneath the overpasses, that in some cases, has left these people with permanent disabilities. Don't take shelter under a highway overpass from a tornado! Image credit: KFOR.com.
Figure 3. Radar reflectivity image taken at 6:08 pm CDT May 19, 2013 of the supercell thunderstorm that spawned the Shawnee, Oklahoma tornado.
Figure 4. Doppler velocity image taken at 6:08 pm CDT May 19, 2013 of the supercell thunderstorm that spawned the Shawnee, Oklahoma tornado. Note the couplet of dark red colors right next to light blues near the center of the image, showing that the air was moving both towards the radar and away from it within a short distance, indicating a tight rotation of the tornado's parent mesocyclone.
Iowa's record tornado-free streak ends at 359 days
A tornado touched down near Slater, Iowa at 6:10 pm CDT on Sunday, May 19, one of six tornadoes reported in the state that day. Remarkably, it was the first tornado recorded in the state since May 24, 2012 (Fayette County.) The 359-day streak without a tornado was the longest tornado-free period in state history. The previous record was 355 days, set between May 5, 1955, and April 26, 1956. The new streak is far more impressive because digital technology and spotter networks today are so comprehensive, resulting in far fewer missed tornadoes. There was a much higher likelihood back in the 1950s for tornadoes to be missed. The exceptional tornado-free period was due to the combination of the state's dry summer of 2012 (3rd driest on record) and cold spring of 2013 (8th coldest March - April on record). Thunderstorms like heat and moisture to form, and its tough to get a tornado if you're experiencing a top-ten driest or coldest spring or summer.
Figure 5. Radar reflectivity image of the tornado-spawning supercell thunderstorm that dropped an EF-1 tornado just to the southwest of Wichita, Kansas, on May 19, 2013.
Wichita gets lucky
At 3:30 pm Sunday, Kansas' largest city, Wichita, got a major scare when a large supercell thunderstorm spawned a half-mile wide tornado to the southwest of the city. The tornado headed directly for the airport and downtown Wichita, prompting the issuance of "Tornado Emergency" for the city. In the wake of the deadly EF-5 tornado that leveled Joplin, Missouri in 2011, the NWS decided to give local NWS offices the option to issue special, strongly worded tornado warnings to let the population know when a particularly dangerous tornado--one that has been confirmed by spotters to be on the ground--is approaching. The NWS issued one of these very strongly-worded tornado warnings on Sunday for Wichita:
Statement as of 3:47 PM CDT on May 19, 2013
... A Tornado Warning remains in effect for southern Sedgwick County until 415 PM CDT...
... Tornado emergency for Wichita...
At 345 PM CDT... a confirmed large... violent and extremely dangerous tornado was located on the southwest side of Wichita... and moving northeast at 30 mph.
This is a particularly dangerous situation.
Hazard... deadly tornado.
Source... weather spotters confirmed tornado.
Impact... you could be killed if not underground or in a tornado shelter. Complete destruction of neighborhoods... businesses and vehicles will occur. Flying debris will be deadly to people and animals.
Locations impacted include...Maize... downtown Wichita... Wichita... Bel Aire... McConnell Air Force Base…east Wichita and Oaklawn.
This is an extremely dangerous tornado with complete devastation likely. You could be killed if not underground or in a tornado shelter. Do not delay... seek shelter now! If no underground shelter is available seek shelter in an interior room of the lowest level of a structure... or if time allows... consider moving to an underground shelter elsewhere. Mobile homes and outbuildings will offer no shelter from this tornado.
Tornado damage threat... catastrophic
Wichita TV station KSNW did an excellent job covering the tornado, but were forced to abandon the studio during the height of the storm, as seen on this video clip. You can hear hail pounding the roof as the news crew scrambles for shelter. Station meteorologist J.D. Rudd has this to say: "We are okay. I'll tell you though, it got intense. That thing passed right over our studio. Luckily, it had lifted. But I truly thought the roof of our studio was about to peel off. And the sound of the hail was deafening. What a day. Three hours of coverage with the largest city in the state under a TOR warning for a long time. Weather service called it a Tornado Emergency…'Large, violent tornado on the ground'. Words that gave me chills when I read them." Preliminary damage surveys from the NWS indicate that the Wichita tornado was an EF-1 with a path length 4.6 miles that lifted two miles south of the Wichita airport.
Figure 6. Severe weather outlook for Monday, May 20, calls for a "Moderate Risk" of severe weather over much of Oklahoma, and portions of surrounding states. You can follow today's severe weather outbreak from our Severe Weather page.
Another big severe weather day today in the Midwest
The latest forecasts from NOAA's Storm Prediction Center call for an active severe weather day again on Monday, with a "Moderate Risk" of severe weather over much of Oklahoma, plus portions of Southwest Missouri, Northwest Arkansas, and extreme North Texas. The highest threat for tornadoes will be in Southern Oklahoma and into North Texas. The severe weather outbreak will continue on Tuesday and Wednesday, progressing eastwards into the Ohio Valley and Great Lakes. Only a "Slight Risk" of severe weather is expected those days.
Video 1. Impressive footage (peaking at 4:30 of the video) of the huge tornado that devastated Carney, Oklahoma on May 19, 2013.
Video 2. The "Dominator 3" armored tornado intercept vehicle saw plenty of action on Sunday, as seen in this video, taken just northeast of Edmond, Oklahoma. From the http://tvnweather.com/ description of the video: "This tornado was one of the strongest ever intercepted, and we needed all 10,000k pounds of the new Dominator because I have never felt vibration like that before as we were slammed by suction vortices wrapping all around the vehicle. Jim Cantore was on board and he's hooked. All part of #TornadoChasers, Season 2013 coming up this fall on http://tvnweather.com/ondemand"
Wunderblogger Lee Grenci has an interesting post discussing how last Wednesday's Granbury, Texas tornado was able to form in an atmosphere that seemingly had too little wind shear to get a supercell thunderstorm spinning. The Granbury tornado was an EF-4 with 166 - 200 mph winds that killed six people, and was part of a weather system separate from the one that is generating the current Midwest U.S. tornado outbreak.
news9.com out of Oklahoma City had some excellent live helicopter coverage of Sunday's storms, and will likely be out there again today.
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