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2 dead as ‘extremely dangerous’ tornado swarm tears through Oklahoma

Isolated severe thunderstorms were expected Thursday from near Chicago all the way to Houston, but the risk of tornadoes will be very low.

Hail the size of ping-pong balls and winds up to 70 miles per hour hit Oklahoma as strong storms and deadly tornadoes swept across the state late April 19. (Video: Naomi Schanen/The Washington Post)
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At least two people have been killed after a series of destructive tornadoes swept across Oklahoma, authorities said.

The extreme weather Wednesday evening included 15 reported tornadoes, hail the size of tennis balls and destructive straight-line winds to hurricane force. A gust of 84 mph was recorded in Pottawottamie County, Okla. The storms destroyed homes and ripped up roads, and aid groups were working to set up shelters.

Officials said there had been “two fatalities” without giving details and noted that “crews are responding to reported injuries & persons entrapped within their shelters.”

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The regional tornado outbreak, which primarily affected areas south of Oklahoma City, materialized on a day when forecasters weren’t even sure storms would form. A lid of warm air — known as a “cap” — was present 3,000 feet above the ground. That worked to prevent pockets of surface air from rising and blossoming into storms.

During the late afternoon, however, the cap broke — and the atmosphere’s pent-up instability was released.

A number of rotating supercell thunderstorms formed along the H.E. Bailey Turnpike southwest of the Oklahoma City metro area, dropping hail the size of baseballs near Chickasha and Amber. A second supercell, resembling a floating, rotating birthday cake with tiers formed by warm, moist air spiraling skyward, passed over the University of Oklahoma in Norman. Forecasters at the local National Weather Service office and the Storm Prediction Center snapped photos of the storm from their homes and neighborhoods.

Tornado activity ramped up shortly after 7:30 p.m., when an influx of jet stream energy aloft helped brew a change of wind speed and/or direction with height. That meant any thunderstorms that were tall enough to span multiple layers of atmosphere would rotate profusely.

Around then, a strong tornado touched down in the city of Cole, located in McClain County about 10 miles southwest of Norman. The National Weather Service described the cone-shaped twister as “confirmed large and extremely dangerous” at 7:39 p.m., noting that it was moving east at 30 mph.

A blue splotch appeared on weather maps where radar detected irregular shapes of objects in the atmosphere — unusually, jagged shapes indicative of debris lofted by the tornado. That “debris ball” was centered over the community of Cole.

That tornado was expected to barrel toward Interstate 35 to the east, but instead quickly swung to the north in an abrupt left turn, in the process sparing the town of Goldsby. A new circulation formed to the south near Slaughterville, the first of several “handoffs” as a new, developing area of rotation replaced a dying area of spin.

After crossing Interstate 35, the storm began exhibiting “deviant tornado motion,” characterized by tornadoes moving in virtually every direction, especially during handoffs. At one point, three distinct mesocyclones, or areas of rotation — each of which could have spawned a tornado — were orbiting one another.

The National Weather Service in Norman issued a spattering of overlapping tornado warnings, struggling to predict which way any of the tornadoes would travel. Strong tornadoes appear to have hit Etowah, Pink and possibly Shawnee.

In Shawnee, Oklahoma Baptist University reported “significant” damage to its campus and said it was relocating students but added that no injuries had been reported. Classes were canceled Thursday and Friday, with power lines down and “significant” debris scattered around the city.

“THE STORM IS EXHIBITING A FUJIWHARA EFFECT, WITH THE CIRCULATIONS ROTATING AROUND EACH OTHER,” the Weather Service office tweeted at 9:51 p.m. Central time. “DO NOT ANTICIPATE STORM MOTION. TAKE COVER IF YOU’RE IN THE WARNING.”

The Fujiwhara effect describes the tendency of low pressure systems in meteorology — weather hurricanes, mid-latitude storms or even vortices as local as tornadoes — to orbit one another. Ordinarily, the unusual tango will persist for a period before a weaker circulation is absorbed into a more dominant area of spin.

Most commonly, the Fujiwhara effect accompanies a “cycling" supercell, when one member of a tornado family withers and a new tornado forms to replace it. What made Wednesday night’s storms unusual was how long the circulation survived, and the presence of multiple circulations ongoing simultaneously.

Leading up to the tornado outbreak, Oklahoma was only included in a level 2 out of 5 “slight” risk for severe weather — and not even a marginal tornado threat was anticipated in southeastern parts of the Sooner State. The unexpected strong tornadoes probably developed as a result of a “mesoscale” feature — something on a local to small-scale regional level that was overlooked by weather models.

Additional tornadoes were reported in Texas, Iowa and Kansas.

Isolated severe thunderstorms were expected Thursday from near Chicago all the way to Houston, but the risk of tornadoes will be very low. Gusty to locally damaging straight-line winds will be the main concern.

Meanwhile, emergency crews in Oklahoma were working to restore power, with some 20,000 people without electricity early Thursday in Oklahoma, according to PowerOutage.us, which monitors outages.

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The Red Cross in Oklahoma said on Twitter it was “opening shelters for people affected by tornadoes that hit Oklahoma communities” in Shawnee, Noble and Washington — all in central Oklahoma.

During the height of the outbreak, the University of Oklahoma warned its students and staff to take shelter and stay indoors.

While tornadoes occur all over the world, the United States experiences more than any other country — roughly 1,150 to 1,200 per year on average. Many tornadoes form in the country because its geography and climate bring together the key ingredients for storms: a mix of cold, dry and warm, humid air. Potent jet stream disturbances, meanwhile, can set those storms spinning.

Deadly tornadoes killed at least 24 people this month after carving a path of destruction in the South, Midwest and Mid-Atlantic.

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