Instruments Inside a Tornado

Among the damage from a cluster of tornadoes on Oct. 4, 2013 in northeast Nebraska, northwest Iowa and southeast South Dakota was a package of weather instruments at the Wayne, Neb., airport.

(RECAPS: Meteorological timeline | News recap) 

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According to meteorologists from the National Weather Service office in Omaha, Neb., the Automated Weather Observation System, or AWOS, recorded its last data at 5:15 p.m. on Oct. 4, before the tornado heavily damaged the instruments. 

The post-storm damage survey found EF4 damage just southwest of the airport, with estimated winds up to 170 mph. Debris from the mangled AWOS was scattered so widely that recovery of the data is not expected, according to NWS-Omaha.

This brings up the question: Have we recovered data from weather instruments hit by tornadoes before?

Let's step through a few recent examples, starting with a November tornado.

NEXT > Tipton, Okla., November 2011

Nov. 7, 2011: Oklahoma

A 1986 study by J.T. Schaefer, D.L. Kelly and R.F. Abbey calculated the risk of a direct hit by a tornado at any spot in the U.S. each year is 0.0004 percent.

Despite those odds, two separate weather instruments were each hit by a separate tornado in the same state on the same day. 

Arguably the most impressively dense network of surface weather stations in the nation is in the Sooner State. The Oklahoma Mesonet (Twitter | Facebook) consists of 120 automated stations, each with a pack of weather instruments and a 33-foot-tall tower to measure wind speed.

On November 7, 2011, a supercell spawned a tornado near Tipton, in far southwest Oklahoma. Also located near Tipton is an Oklahoma Mesonet station.

A peak wind gust of 86.4 mph was measured before it was destroyed. If the towers weren't destroyed by wind-borne debris, higher wind speeds most certainly would have been measured. 

You can see a plot of the station's pressure (top) and winds (bottom) in the image below. The passage of the tornado is marked by the sharp downward spike in pressure and upward spike in winds. Not only was an 86 mph gust measured, but an astonishing pressure drop of 47.16 millibars in just one minute was recorded.

Incredibly, according to a 2008 paper by S.F. Blair, D.R. Deroche and A.E. Pietrycha, a 194-millibar pressure drop was measured by a mobile mesonet vehicle in the April 21, 2007, tornado in Tulia, Texas. Peak wind speeds to 112.7 mph were clocked in this case.

To place this in perspective, the central pressure of Hurricane Wilma, the most intense Atlantic hurricane on record, dropped merely 54 millibars in six hours, an astounding rate for a tropical cyclone, but paling in comparison to the pressure cratering that was sampled in Tulia, Texas, in 2007.

We mentioned there were two instruments hit on the same day. That same supercell later spawned another tornado near Fort Cobb, Okla., damaging another Oklahoma Mesonet site due to wind-borne debris.

The Fort Cobb station measured a stronger peak wind gust (91.4 mph), but a more gradual pressure drop (about 14 millibars). 

"Never in (Oklahoma) Mesonet history has a site been leveled by a tornado, but it appears to have happened twice yesterday (Nov. 7)," said Dr. Chris Fiebrich, Oklahoma Climatological Survey associate director for the Oklahoma Mesonet, in a blog post the following day.

This wasn't the only time this happened in Oklahoma in 2011!

NEXT > El Reno, Okla., May 2011

Close Encounter With an EF5 Tornado! 

Less than six months before the Tipton and Fort Cobb tornadoes, an EF5 tornado passed close to another Oklahoma Mesonet station, but didn't destroy it.

On May 24, 2011, more than 50 tornadoes tore across the Plains, mainly in Kansas, Oklahoma, north Texas and northwest Arkansas.

One EF5 tornado carved a 65-mile-long path of destruction from near Hinton, Okla., to north of Guthrie, Okla. 

In the path was a mesonet site near El Reno, Okla. 

While mobile Doppler radar from the University of Oklahoma measured wind speeds well over 210 mph with this massive, wedge tornado, the circulation's strongest winds remained just far enough away to spare the instrumentation. As you can see in the photo at right, only a scrap of sheet metal wrapped around the apparatus. 

As it happened, the tornado passed just north of the sensors, but remained "within the outer edge of the damage path," according to Oklahoma Mesonet technician Phil Browder. "A piece of metal wrapped itself around our tower ... from where ... we have no idea," said Dr. Christopher Fiebrich, associate director for mesonet at the Oklahoma Climatological Survey. "The tower stood perfectly tall. No damage to the official wind sensor."

That wind sensor clocked a maximum gust of 150.8 mph (see the graph above), with an average one-minute wind speed of 115.3 mph. This gust set a record fastest wind speed recorded by the Oklahoma Mesonet, wind speeds equivalent to an EF3 tornado, on the periphery of the circulation (the tornado was rated EF5, as mentioned before). 

Incidentally, it was also in Oklahoma that the Doppler-on-Wheels mobile research radar measured an incredible 301 mph wind gust in the May 3, 1999, Bridge Creek tornado, although that was, thankfully, measured at some altitude above the ground.

(MORE: May 3, 1999 outbreak was one of nation's worst)

Finally, we end with a tribute to a researcher and storm chaser with some incredible measurements inside a tornado.

NEXT> Tim Samaras' Incredible Observations

Placing Probes in a Tornado's Path

We would be remiss discussing instrumentation hit by tornadoes without mentioning the pioneering work of Tim Samaras.

Samaras ran a scientific field research program known as TWISTEX (Tactical Weather Instrumented Sampling in Tornadoes EXperiment). An engineer and storm chaser, Samaras built instrumented probes to deploy in the path of tornadoes. 

Perhaps his crowning achievement was his cone-shaped probe's measurement of a 100-millibar pressure drop in the F4 Manchester, S.D., tornado of June 24, 2003.

Almost 10 years later, Samaras, along with his son Paul and long-time colleague Carl Young, were killed chasing the multi-vortex El Reno, Okla., tornado of May 31, 2013.

(MORE: Weather Community Mourns Loss of Storm Chasers | Tornado Recap)

In the 1980s, scientists from the National Severe Storms Laboratory in Norman, Okla., built a totable tornado observatory, dubbed "TOTO." This was, in a nutshell, a portable mesonet instrument package, weighing about 250-350 pounds, that could be moved quickly off the back of a custom pickup truck and placed in the path of a tornado.

TOTO was deployed close to a weak tornado on April 29, 1984, near Ardmore, Okla., according to NOAA's Storm Prediction Center, but tipped over easily.

TOTO had little success directly measuring a tornado's winds, owing to the difficulty of quickly and safely deploying it in precisely the right spot, then getting out of harm's way. TOTO was retired in 1987.

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