Tornadoes and vehicles

The death toll from the December 26 tornado event in the DFW metroplex stands at 11.  All eight victims in the Garland area, near the President George Bush Turnpike and Interstate 30, were caught in their vehicles.

This tragedy should not surprise anyone familiar with past killer tornadoes.  Just in Oklahoma and bordering towns:

5/1/1954, Cotton County:  Two killed trying to escape a tornado in a pickup
7/15/1955, Sulphur:  One killed, two injured in a car at a drive-in
4/2/1957, Murray County:  Truck thrown from Route 77; driver killed
4/2/1957, Marshall County:  Car thrown over 200 yards; one killed, one injured
5/5/1960, McIntosh County:  Two killed, five injured; caught while driving to neighbor's cellar
5/5/1960, near Fort Smith, AR:  Transport truck lofted from Route 64; driver killed
5/26/1973, Muskogee County:  Truck thrown/rolled half a mile; four killed
4/10/1979, Wichita Falls, TX:  25 vehicle-related fatalities in F4 tornado; only five in homes
5/15/1990, Stillwater:  One killed while driving to shelter at friend's house
4/26/1991, Pawnee County:  Cars blown from Cimarron Turnpike; one killed
4/26/1991, Copan:  Car thrown 250 yards; one killed, one injured
5/3/1999, OKC metro:  Two killed, many injured at highway overpasses
5/3/1999, Payne County:  Car lofted from beneath I-35 overpass; driver killed
5/10/2008, far SW Missouri:  Multiple vehicle fatalities from Picher, OK tornado
2/10/2009, Carter County:  Driver of truck on I-35 killed by Lone Grove tornado
5/10/2010, Moore/OKC:  One killed trying to escape Lake Draper tornado
5/24/2011, Calumet:  Three killed on I-40 by EF5 El Reno/Piedmont tornado
5/19/2013, near Shawnee:  One killed in vehicle
5/31/2013, near El Reno:  All eight tornado victims were in vehicles

Encounters between drivers and tornadoes seem to fall into two categories:

1.  Locals trying to evacuate or reach safe shelter by car

This is a pure social science problem.  There is a dangerous myth that some tornadoes are so strong as to be unsurvivable above ground.  In reality, in the May 3, 1999 Bridge Creek-Moore-OKC tornado, 99% of people in homes sustaining F4 or F5 damage survived (Hammer and Schmidlin 2002).  Mobile Doppler radar observed an unimaginably violent 318 mph peak wind speed in that tornado.  While not all houses receiving high-end damage experienced winds quite that extreme, it's fair to conclude that if the May 3 tornado was easily survivable above ground, any tornado is.

Let me say that again, because it's important:  In one of the most intense and destructive tornadoes ever seen, 99% of people sheltering in the hardest-hit houses survived.  If a tornado is headed your way, the odds are against it being an EF5.  Even if it is, most of its track will not experience the peak EF4-5 winds--the odds are still against your house sustaining EF4-5 damage.  So if you're following appropriate tornado safety guidelines in a reasonably well-built home, you have reason to believe your chances of riding out an approaching tornado above ground are actually much better than that 99%.

That's not to say that nobody should drive to safer shelter.  Not everyone is in a well-built house, office, or large public building.  Mobile home residents, people working in areas without sturdy buildings (like oilfields), and others may have no choice.  As the following graphic from NWS Norman stresses, it's critical for people in such situations to closely monitor weather information and put their plans into action before a tornado warning is in effect at their location.  Lead time with a tornado warning is typically 20 minutes or less.  That's too late to take to the road. 

2.  Motorists unaware of the danger

This describes a couple of the El Reno fatalities in 2013, and probably at least some of those in Garland.  Anyone who's driven around the DFW metroplex can attest that trips often take much longer than the time scale of a tornado warning.  The area is a perpetual traffic jam even in fair weather.  Highway signs with up-to-the-minute messages can be of some use in alerting drivers to the existence of the threat, but can't convey details or maps.  Even if drivers receive a tornado warning, around population centers it may be impossible to get them all off the road and into sturdy shelter in a matter of minutes.  Being on a bumper-to-bumper highway when a warning is issued is a worst-case scenario.  Making sure it doesn't happen calls for weather awareness well before the warning.

For both categories, the underlying issue is that many people don't act until they become aware of a tornado warning for their location.

Surviving a severe weather event begins long before a warning comes out.  There are a number of products issued by the NWS, like convective outlooks and tornado watches, that provide severe weather awareness days to hours in advance.  These products can't pinpoint locations down to the town and times down to the minute.  What they can do is help people in the risk area avoid desperate situations.  As long as occupied vehicles are being lofted by tornadoes, those products aren't achieving their goal.

A tornado watch means that the broader environment will be favorable for tornadoes over the coming hours.  It's your cue to make sure you can quickly receive warnings and seek shelter if need be.  A tornado warning means that a specific storm moving into your specific location either is producing a confirmed tornado or has a radar signature that strongly suggests one.  A warning doesn't mean "Drive to a place where you can seek shelter."  It means "Shelter right now!"  In the current state of the science, there is no official product between the watch, which has a lead time of hours, and the warning, which has a lead time of minutes.  That means that when you're in a watch box, you never want to be without means of receiving tornado warnings instantly, or more than a few minutes from some kind of shelter.  Being on the road makes it harder to get warnings and other information, harder to be sure exactly where you are in relation to the threat, and harder to get to safe shelter quickly.

16 November 2015 Panhandle tornadoes

Addison and I loaded up and departed immediately after class.  Norman was cold, overcast, and misty.  We had been considering a target of Childress, TX, earlier in the morning, but were both leaning toward playing farther north along the I-40 corridor as the theta-e axis nosed northward.  We agreed on a target of Groom, TX, as we left the National Weather Center.  Convection struggled to become established in the modest instability and strong shear typical of late fall Plains events, giving us time to reach the Panhandle.

Near the western Oklahoma border, we broke out of a thick deck of low stratocumulus and the temperature jumped.  We arrived at the interchange where Hwy 70 goes south to Clarendon and surveyed some high-based thunderstorms that for some reason were barely clinging to life.  It could have been that the strong heating west of the cloud deck had mixed out too much low-level moisture, but we weren't sure.  Regardless, a supercell had formed between Amarillo and Lubbock, and it was becoming clear from radar data that that storm was our only chance of seeing anything worthwhile before dark.

The Texas Panhandle is not the iron-flat, grid-road holy land of storm chasing I once thought it was.  That does exist on the Llano Estacado, the high plain west of the Caprock Escarpment.  But the eastern half of the Panhandle is dominated by river valleys--the Canadian and the forks of the Red--all of them extensive obstacles for chasers.  We found ourselves stuck southwest of Clarendon on the rim of a wide, shallow valley where the Prairie Dog Town Fork and its tributaries flow (at least when it rains).  The supercell churned behind the opposite rim of the valley, maybe 20 miles distant.  As the sun sank along the storm's southern flank, it provided adequate contrast for us to see a rain-free base with fingers of cloud reaching down, moving around, and changing shape.  At such a distance we could only speculate about what we were seeing.

Desperate to intercept somewhere before nightfall, we backtracked to Clarendon and headed northwest on U.S. 287, a wide open stretch of highway with which we'd become familiar on a PECAN deployment in the summer.  With the storm moving northeast, we pushed on until we approached the forward flank.  A funnel appeared in front of us and reached toward the ground; by the time we pulled over, it had almost retreated back to the cloud base.  Other chasers confirmed a brief tornado.

We stopped just short of the RFD gust front at Goodnight (where Charles Goodnight of the Goodnight-Loving Trail is buried) and observed for a few minutes before turning north on Ranch Road 294.  The outflow was bearing down from the west, a second storm was forming behind ours, and darkness was gathering.  By lightning we saw things beginning to happen far to our north-northeast and pulled over.  The first photo had to be brightened a lot and shows a pronounced clear slot wrapping around the incipient funnel cloud.  Rain and wind slammed us while we tried to document the tornado.  It's not visible in my photos, but we saw a debris cloud at the surface backlit by lightning.  Addison called it in to NWS Amarillo.  This tornado was very close to Groom, the target we had set in Norman and the site of my 16 April tornado intercept.

This tornado dissipated and we continued north to I-40, on which we headed east.  The supercell was gaining forward speed and we weren't sure how long we could stay with it, or if we'd be able to intercept again at all.  But as we went east through Groom and Alanreed, lightning allowed us to view another tornado maturing to our north.  It grew from a cone into a stovepipe and persisted until it moved out of view.  Addison called AMA again.  We didn't take photos, since there were few stopping places on I-40 and we hoped to catch the storm again.  Watching radar, we continued to eye a second storm right on the heels of the first.

We turned north at McLean, TX, on Hwy 273.  The first part of this highway was straight and desolate.  This was the little Pontiac's first storm chase, and it got to stretch its legs with storms racing away from us at 50+ mph.  We caught a break, though:  the second storm organized quickly and produced a tornado.  The velocity signature wasn't immediately obvious as it was passing near a wind farm, but one scan showed a long faint hook in reflectivity and the next showed a high-reflectivity ball at the end of it.  We decided to let the lead storm go, even though the tornado we'd seen from I-40 was now a monster near Pampa, and play the closer one.

The road turned northwest toward Lefors and Pampa.  Coming over a rise, we saw the wedge on the lead storm far to our north.  By the time we got out and took photos, it had all but disappeared over the horizon, but at least the top of a big tornado is evident.

There was a single power flash to our west with the new tornado as we flew northwestward.  Where 17 Road meets Hwy 273 just north of Lefors, we got our best look at Pampa tornado #2 as it moved along the southern fringes of Pampa about eight miles to our northwest, doing EF-3 damage.  Rapid rising motion along the edges of the condensation funnel was visible even by lightning.  It was the strongest tornado either of us had seen in person to date, with peak winds estimated at 155 mph and a maximum width of 750 yards.  AMA got a third phone call and a tweet, but everyone in the Panhandle knew what was going on by that time.

We decided the storm, which was still blasting northeastward at highway speeds, was worth following farther into the night.  Getting to the southwest-northeast U.S. 60 would offer us a chance to stay with it.  The northward jog on the gravel 17 Road was hairy at times.  The remote farmland was extremely dark, and sharp curves caught me by surprise.  We were lucky to stay on the road.  Driving on unfamiliar roads in a hurry, distracted, and/or at night is a greater danger than the storms, especially for conservative chasers.  After thumping over several cattle guards, we emerged on Hwy 152 and cut over to U.S. 60 east of Pampa.

At this point we became concerned.  Emergency vehicles with lights flashing were hurrying back and forth.  It was evident that significant damage had occurred somewhere.  We later learned that the tornado had destroyed a Halliburton plant less than five miles west of the intersection.  Just after turning northeast on U.S. 60, all at once we noticed power lines lying on the road, a defoliated tree, and the pungent smell of freshly ripped grass.  In hindsight, this was likely the track of the first Pampa-area tornado, not the second.  Seeing no structures in the area where our help might be needed, we continued behind the storm.  Lightning periodically showed us a large tornado; a damage survey would conclude that the Pampa tornado had actually dissipated and we were following a new one.

We stopped somewhere near Miami for a final view.  Far off on the horizon, there appeared to be two tornadoes side by side.

The town of Canadian, farther northeast on U.S. 60, marked the end of the chase.  We were running low on gas and unable to make out any more interesting features on the storm.  We dropped south to get gas and snacks in Wheeler, then raced through Shamrock to I-40 as a congealing QLCS spun up weak mesovortices all around us.  Even with a speed limit of 75 in the Panhandle, not until the Oklahoma border was there a comfortable cushion between us and the leading edge.

Per NWS Amarillo's final public information statement on the event, nobody was injured in these tornadoes, even though two EF-3s brushed Pampa.  Photographically it was a rough night, but it's impossible to complain about catching nocturnal wedges in November.  No tornadoes as strong as these had ever been recorded so far west and so late in the year.  Five or six tornadoes in a day is also a personal best.

 

To the best of our knowledge, we at least saw tornadoes 1, 2, 4, 5, and 6 on this map.  It's possible that 6 and 17 were the "twins" we observed from near Miami.