November to Remember
Tornadic Supercell in Southwest Oklahoma
7 November 11
SHORT: Intercepted two nontornadic supercells and one tornadic in SW OK. Witnessed multivortex tornado move through wind farm, among others.
LONG: This has been a very fortunate year for me for storm observing, and a rare juxtaposition of a day off with a November chase day offered the promise of icing on the fine tornadic cake that has been 2011.
Pre-storm
For several days, a classical, spring-like, near-dryline supercell setup appeared to be looming…in autumn. Looking at the morning charts and RAOBs, the presence of very nearly surface-based effective inflow parcels even during early-mid morning (using FWD and OUN soundings) reinforced my main concern–the potential for early initiation, maybe too many storms too soon. Otherwise the foci for supercell and tornado potential looked fairly well-defined, the target area compact: approaching, progressive shortwave trough aloft with deep-layer shear strengthening throughout the day, adequate moisture return, backed winds, and enhanced low-level vorticity along an outflow boundary E of a dryline and cold front…all in the southwest OK/NW TX area.
After morning appointments (I try to avoid scheduling any immovable commitments for afternoons even in the “off-season”), visible imagery showed good clearing from the southern tier of OK counties (LTS-FSI) southward, and towers already starting to deepen in the weak CINH even before noon. The deepest warm-sector convection already was forming near 100W (TX/OK border longitude), with other clumps of shallower convection farther ESE over NW TX. Time to head out the door!
Early, non-tornadic supercells
Perhaps I left a little too soon; this is a longstanding bias of mine. Still, I targeted the LTS area via the NE (HBR) instead of E (FSI), in case any decent storm rode up the western fringe of OK and into the baroclinic zone. I’ve had a few successes with early-event tornadic storms tucked in the NW side of a SE-expanding storm regime, and a supercell SW of Mangum was getting larger.
By the time I reached Lone Wolf, on the way toward Mangum, a messy cluster of storms with some banding and supercellular tendencies had formed to the SW (wide-angle). I considered staying near there, and perhaps should have in hindsight, given a few observers’ later reports of a short-lived multivortex tornado with an eventual supercell SW of HBR. Instead, I headed to the western storm, somewhat concerned that my onboard thermometer indicated only the narrowest of slivers of diabatic warming between the HBR cluster and the now tornado-warned Mangum storm.
The western storm came into view NW of Mangum; I parked 2 WSW Brinkman to let the storm move just to my W and N. It was somewhat pretty, but not too promising. An earlier, distant wall cloud had vanished, and the storm looked rather strung-out. A new mesocyclonic cycle yielded a weakly rotating, nice-looking little wall cloud, but it couldn’t tighten up and produce. Moreover, the probability it would was dropping by the minute; inflow air was getting cooler! Naturally, the storm started to weaken.
By this time, a small cell I earlier had noted on radar, S of the Red River and S of FDR, had exploded and was taking on obvious supercellular signatures. I was out of position for anything it would do in the next 1-1.5 hours, and knew it. But I also knew it would have a long potential trek through vorticity-rich air of at least marginal buoyancy, all the way N of the Wichita Mountains, if no other storms erupted to its S or SE. For now and for hours, that southeastern storm would remain unimpeded that way.
I wasted no time in deciding to go toward the FDR storm, but two other supercells were in the way: one just SW of HBR (the early multivortex producer I missed) and the other slightly farther SW, also approaching HBR. My best chance at shooting the gap between these two supercellular obstacles and stay on course for the southeastern storm was to head back through Lone Wolf to HBR, around the northern flank of the southern-middle storm and S of the hook of the northern one (beautiful rainbow scene on their collective W side). I threaded between the two most dense core regions; but the gap was small and I did encounter some small to marginal-severe hail in the southern (nontornadic) HBR storm’s forward flank. Here’s a wide-angle look at the southern-middle storm between HBR and Roosevelt, looking WSW.
Turning S out of HBR, my timing looked barely adequate, and more likely too slow, to reach the FDR storm S of the Wichitas. By now, I already had heard of a couple of tornadoes it had produced; and the storm appeared to be trucking along nicely with a powerful low-tilt velocity signature. Instead of trying to stern-chase it on US-62, only to encounter a road void in the Wichitas, I chose to head E out of Roosevelt, skirt the storm’s northern flank, and wait N of the Slick Hills for the supercell’s business end to come toward me. I knew the massive, E-W oriented Blue Canyon Wind Farm was a couple miles S of OK-19 too, right in the meso’s path, and might provide an interesting foreground for whatever emerged from the rough terrain. It would be my first correct strategic decision all day.
Post-Wichitas phase of tornadic supercell
Heading E from Roosevelt, I could see some of the rear-flank convective wall of the FDR supercell to my S; while a very bright rainbow with secondary accompaniment festooned the fringes of its left-flank precip core. I zigzagged the necessary roads toward the area NE of Saddle Mountain, encountering more mainly sub-severe hail in the tornadic storm’s northern rim. The hook echo was very impressive on radar, when I had any phone data in this reception-deprived area, with one scan of ~100-kt gate-to-gate shear. By now, I was preparing for the possibility of a big tornado coming out of the mountains and through that wind farm.
A fine viewpoint appeared ~5 SW Alden on OK19, with a surprisingly green field of winter wheat leading SW toward the ridge-top wind farm. The mesocyclone’s orbiting rim of cloud-base scud came into view to the SW, circulating at impressive peripheral speeds that I’ve seen only with tornadic settings. The meso was translating directly toward me, but still with plenty of time to spare and a good escape route eastward. Time to rock and roll. Alas, a furious bombardment of close CGs kept me under within the vehicle for several more minutes. A group of unrecognized chasers showed up at the same vantage, standing outside rather unwisely despite the occasional CGs still hitting within hundreds of yards.
Fortunately the electrical attack from above abated fairly quickly, and we all could concentrate again on the approaching mesocyclonic menace. I was very confident a tornado still was lurking beyond the ridge line near Saddle Mountain; and within minutes, that suspicion was confirmed! The visible condensation funnel of the tornado, still beyond the ridge, vanished from obvious view for a minute or two, the visible parts of the cloud base seemingly boiling with furious movements. The tornado reappeared even better. I strongly suspect this was the same tornado as before, given
1. Its temporal and spatial continuity relative to the ambient mesocyclone circulation, and
2. Later TV-chopper videos I’ve seen of the Saddle Mountain tornado, which dissipated right before reaching the wind farm.
A new, strongly rotating wall cloud formed N of the dissipated tornado and over the western part of the wind farm. In fact, its base was so low that the turbine blades extended into the cloud! The new circulation also extended E of the visible wall cloud, which seemed to subsist on recycling of rain-cooled air from the precip wrapping around the N and NW sides of the hook. This fascinating process was about to get more so, and fast.
On the E (left) side of the mesocyclone, slightly displaced from the lowest part of the wall cloud, a multiple-vortex tornado, containing a dominant central condensation tube, developed over the wind farm. This was obviously separate from the earlier tornado. Since some of my home’s power comes from this wind farm, I was hoping against its destruction; in fact, as the tornadic circulation continued to swirl through and around the turbines (wide view and cropped), I saw no clear evidence of damage.
Small suction vortices occasionally formed and pirouetted gracefully among the turbines (wide view and cropped), as the main cone became more sharply defined (wide view and cropped). The entire scene was strange and ironic — a wind farm under siege from the ultimate in “wind power” (wide view and cropped).
Through the whole ordeal, the disabled blades held firm, not budging nor popping loose, despite the undoubtedly intense mechanical stresses. The functional turbines seemed to adjust their alignment (with some lag) to the mesocyclonic wind shift, but of course, couldn’t do so fast enough at tornado-vortex scale. The blades’ rotation speed seemed to remain fairly steady, which fits the purposeful design of such machines to brake the spin rates in order to minimize damage in extreme wind. This certainly qualifies as extreme wind!
A powerful, precip-laden RFD surge hit the tornado, weakening it while sending the remains of the circulation careening ENE through the N side of the wind farm, at an oblique angle. A newer mesocyclone was tightening up rapidly, immediately (just over a mile ) to my SW, so it was time to reposition a tad east. While driving, a glance in the right-side rear-view mirror revealed a new, entirely separate tornado developing as a tall, slender tube. This pretty, partially rain-wrapped tornado (the third for me so far) only lasted a couple of minutes, dissipating as it reached OK-19 near where I had parked before.
This newest mesocirculation, with wrapping rain curtains, shot toward the NNE beyond OK-19. I headed E a little over a mile to OK-58 then N, watching it weaken as it obliquely approached the road to my immediate WNW. The mesocyclone dissipated fast. Still, rain curtains seemed to be moving fairly quickly in assorted directions around me. Frequent glances at the cloud base above revealed strengthening, convergent westerly flow. I soon saw why.
Yet another quick occlusion was about to occur, as another mesocyclone developed a short distance to the E. This was not the optimal position for any storm observer to occupy, so I searched for a good E option that would take me out of the backside of the hook. [Fortunately, the storm continued its trend of producing non-damaging hail with respect to my vehicle.] Now WNW of the new circulation, I turned E on E1380 Road toward “Pine Ridge”, a crossroads with neither a ridge nor pines. The road was reasonably well-drained, alternating between paved and hard-packed gravel with occasional shallow puddles, and was good to go at 50-55 mph in high 4WD.
Right after my turn, a fuzzy cone tornado materialized to the ESE, allowing a brief stop to photograph it before the rear-hook firehose started dousing me. The white smudge in the last shot, below and to the left of the tornado bottom, was a hail splash.
Back on the road again, I carefully approached the mesocyclone and tornado from the W, watching the latter dissipate and the former rotate intensely as it crossed E1390 about a mile away. This circulation moved N, and yet another one (the eventual Ft. Cobb tornado producer) developed just to its E. By now, the storm definitely was translating poleward and speeding up, getting away from me even as I drove the short few miles to my N turn on N2550 at “Pine Ridge”.
Seeing occasional multivortex filaments form under the new circulation (the Ft. Cobb tornado), I stopped briefly to photograph the storm structure with the mesocyclonic cloud base below (deeply enhanced crop-n-zoom). Heading N toward Ft. Cobb, I could see occasional plantings of full ground-cloud condensation; but every one of the 4-5 times I tried to pull over and photograph them, the condensation would go away. Daylight and contrast each grew dimmer also.
After escaping Ft. Cobb, I drew closer to what was left of the circulation near Albert, its cloud base still rotating and low-hanging in the twilight, but obviously weakening. I couldn’t complain much, though, I had found my fifth tornado of the day, a pretty remarkable feat considering some poor tactical decisions early in the afternoon that caused me to miss a fantastic tornado show SW of the Wichita Mountains.
Epilogue
The trip back was mercifully short, as the former FDR-Ft. Cobb supercell got absorbed ingloriously into a building band of storms near Okarche. How often does one arrive home by 7 p.m. after a multi-tornado intercept? Despite what I had missed, these were my latest tornadoes seen in a calendar year, and multiplied by six the sum total of lifetime November tornadoes.
To make the day truly unique, I got to experience an earthquake too. Not long after settling in at the house, a low, thunderous rumble and weak vibrating of the house signaled the magnitude 4.7 aftershock from the Sparks earthquake swarm that had been rattling off and on for several days. I had felt the Oklahoma-record magnitude 5.6 shaker a couple of nights earlier while in a cabin at Greenleaf State Park (my first ever). With multiple earthquakes and tornadoes witnessed in a 3-day span, it was a marvelous time for an earth scientist in Oklahoma. 2011 also has been, by far, my most prolific tornado year.
As with the 20 June tornado-fest in Kansas and Nebraska, I sent an itemized table of tornado times and estimated locations to the WFO, with embedded links to many of the same photos as above. That table includes times, locations and links to the photos. What had been listed as one tornado on coarse-resolution maps, from S of the Wichitas to OK-19, should become three in the final record. The tornado log file is in the public domain, and linked here in MS Excel format, freely accessible for anyone interested.