Bleeding the Turnip: Optimized Success in a Marginal Setup

July 15, 2012 by · Comments Off on Bleeding the Turnip: Optimized Success in a Marginal Setup
Filed under: Summary 

Okeene to Richland OK, Tuttle to Newcastle OK
29 May 12

SHORT: Intercepted entire life cycle of eventual Kingfisher-Piedmont supercell and its tornado, as well as twilight phase of separate supercell near Tuttle.


Nowcasting through initiation

After forecasting the potential for supercell initiation in a meso-beta scale confluence zone, somewhere between the west-central part of the KS/OK border and southwestern OK, Rich Thompson and I set out for the middle-ground target of the Watonga area for what would be our last Two Chumps chase of 2012.

The low-level moisture field over central/southern OK, in the prospective upstream fetch, had been eroded and fragmented by prior convection, so LCLs and cloud bases promised to be somewhat high for much of the day. Low-level flow wasn’t the strongest, either, but deep shear still fell within the margins of supercell and tornado days. Low-level forcing was subtle, but hourly surface streamline analyses revealed that confluence zone and its persistence. It wasn’t a classically straightforward setup at all. In fact, I had sent the following in a private note to a group of friends and associates before heading out: “Messy day–one of those that’s good for a needle-in-haystack ‘misoscale accident’…”. That’s exactly what happened.

The Two Chumps headed NW toward Watonga, encouraged not only by increasing juxtaposition of favorable parameters and foci in that area’s data fields, but also, good ol’ preconvective spotting with the human eyes that showed thicker convective towers in that part of the confluence zone.

In Watonga, numerous storm enthusiasts had accumulated to shoot the bull, empty the bladders and pass the time, with at least one (Conrad Ziegler) on a serious scientific mission. Conrad graciously invited us to a NSSL mobile lab vehicle to see data streaming in real-time from a freshly launched portable sounding. As we were discussing the weakening cap and other interpretive characteristics of the still-plotting RAOB, another use of the eyeball tool proved fruitful. Through the trees behind the Love’s fuel station, we caught a fair view of a very deep tower blowing the lid away to our NNW, near Fairview. Initiation!

Organizing to mature supercell stages

Rich and I cruised NNE to a suitable observation spot just S of Okeene, watching the towers deepen further, glaciate, and evolve into a bonafide cumulonimbus with some great anvil-aided crepusculars. As the storm started to anchor, grow and assume some visual supercell characteristics, we went E of Okeene, in its SE-moving path for a few minutes. We then embarked on a zigzagging trek with a net SE bearing, along well-maintained back roads, in and out of the sunlight, between Okeene, Loyal and Kingfisher. It was a tricky and difficult balance between getting in the storm’s shadow (better viewing contrast) and staying out of the intensifying forward-flank hail dump. In fact, at one point N of Loyal, we were getting subsevere hail in the sunshine!

While observing the twisting soda can of a storm, we were joined for a spell by BC, Ed C, Blufie and Joel Genung. Seldom has there ever assembled a more motley crew of grizzled, longtime, smart-ass chasers on an old dirt road. It reminded me of some friendly June convergences on the High Plains of Colorado, right down to the tan-colored wheat fields and high, roughly textured cloud base; but of course, the red dirt gives away the more southeasterly geography. We even could see the stacked-plate structure and shallow wall cloud of another supercell to the N, through the translucent core of the nearest storm.

Despite the insults and wisecracks dutifully exchanged, it was a pleasure to share several minutes of this young supercell’s lifespan with those guys…until the storm closed in and we had to disperse farther SE. We stopped a couple times between the Loyal area and Kingfisher as the storm expanded its base, produced more precip, and began to tighten up areas of enhanced cyclonic shear with occasional scuddy, slowly rotating lowerings.

Even though the ambient cloud base remained high, each lowering in a long series of them seemed to be a little better organized, condensing a little closer to the ground, thanks to some combination of lower pressure and higher RH, and a little more confidently rotating. This one, seen from S of Oneida, appeared as if it could tighten up to tornadic scale before being undercut by outflow. Nonetheless, that was one of my favorite views from the chase–again very Colorado-like under one of my favorite lighting conditions: looking NE into a high-based storm with little rear-flank precip, well-lit ground and darker forward-flank core area in the rear. That view seems to bring out some of the best texture and scuddy contrast in such storms.

Proceeding briskly southward on a dirt back-road, we were trying to reposition SW then S of the storm when a gustnado formed to our ESE, near the leading edge of the outflow from the nearer mesocyclone’s occlusion process. The resulting tube rose along the inflow-outflow interface and may have gotten involved with the updraft at cloud base (photo looking E, and contrast-enhanced version). If so (and that’s not certain), one could count it, though it was at best a fleeting and ephemeral “cheezenado”. I suppose we could claim it as tornadic if we were keeping score in some competitive tornado-fishing tournament. Fortunately storm observing isn’t like that, nor should it be.

We managed to get S of the storm for a short time as we found a viewing area on the SW edge of Kingfisher, watching an old occlusion to the N (manifest as a broad, outflow-undercut cyclonic shear zone) and a new one to the NE that rotated broadly but was still high-based. Under the latter, a scuddy, conical, slowly turning lowering briefly appeared above some dust–it would have been over the W side of town–but the dust appeared to be translating and not spinning. That’s good for Kingfisher.

Aware of the accumulating hordes of chasers and pseudo-chasers, we stayed off the main roads as much as possible in a SE-bearing zigzag between Kingfisher and Piedmont, remaining mostly S of the storm until reaching OK-3 (NW Highway) W of Piedmont. Meanwhile, reports of huge hail were starting to roll in–not surprising given the long-lived nature of this supercell and the environment it occupied. We had plenty of incentive to stay out of the hail core!

We stopped briefly on a dirt intersection near the Kingfisher/Canadian County line to watch a few short-lived areas of small-scale rotation in the newer mesocyclone, which itself had evolved into an elongated, cyclonic shear zone at cloud base with an ill-defined clear slot and some turquoise-toned precipitation areas. The episodic zones of cloud-base rotation were tighter and stronger than at any prior time in the storm’s lifespan, but still brief, shallow and apparently undercut. The storm acted like it wanted to produce a tornado, but needed some outside assistance.

Tornadic stage

It was during that maneuvering that we began to realize that a left-mover to our SSE was going to crash into the forward flank of our supercell, given their respective, extrapolated motion vectors. More importantly, the outer part of the left-mover’s rear-flank gust front (RFGF), which on radar reflectivity imagery arched NW and W out of its parent storm, eventually would smack into the mesocyclone region of the cyclonic supercell, somewhere not far SSE of us near Piedmont. We surmised that could be the outside assistance, and our best opportunity to see a legitimate spinup.

After all, think about the sign of the vorticity produced by the same relative part of a “normal” supercell’s RFGF: anticyclonic. It follows, therefore, that the same segment of the anticyclonic left-mover’s RFGF will contain enhanced cyclonic vorticity. Infuse any right-mover’s mesocyclone with more cyclonic vorticity along a boundary, and things could get very interesting for at least a few minutes, until the air behind the boundary gets too stable for the right-mover’s updraft to process efficiently.

Yes, we were nowcasting these processes, and charted a course down OK-3 to get just SE of the most likely interaction spot and witness it front-row, ringside. We also reprised an old quote of Rich’s from 1998: “Something out of this is gonna do whatever’s going to happen.” Even after conceptualizing how it could occur, we were amazed that it actually did!

In this shot, the mesocyclone area is seen to our NNW (the road goes NW). The center of the mesocyclone was translating generally SSE toward a spot just to our W. It didn’t look like anything imminently threatening–still with a rather high, ragged cloud base, and a much bigger dump of precip to its N and W than ever. The RFGF from the left-mover was passing our location with a wind shift, behind which we noticed only slight apparent cooling. We maintained position as the mesocyclone approached and the left-mover’s RFGF proceeded into it, saw a radar truck and some other chasers (including media trucks) bail SE past our watch at high speeds, and then…

Within the broader meso, a compact area of cloud-base rotation appeared with a small, tight fan of spinning dust beneath. Tornado! Here’s a wide-angle (full-factor 30 mm focal) within 10-15 seconds after tornadogenesis. Ground circulation was less than a mile to our NNW, time 2018 CDT (118Z), and we were located 3 N of Richland. It had no condensation funnel yet, and wouldn’t for several more minutes as the circulation churned S toward and across OK-3.

This wide-angle photograph shows the circulation with about its greatest dust production, before it rapidly wrapped in rain, crossed OK-3 with a power flash, and spun across wetter ground. The dust, scud above and cloud base were rotating in sync, as was the case when the cloud-base feature began to narrow after crossing the highway. I stood out in the wrapping rain as the weak tornado moved W through SSW of us, shooting wide-angles of the tornadic circulation at cloud base with what little dust it could raise, until 2024 CDT (124Z). At its closest point, the tornado was around half a mile away, with a few embedded subvortices–but never expansive enough to threaten us directly.

Of greater concern was the hail wrapping all the way around the meso–some of which started bouncing off the road around us and looking bigger than two inches. A few minutes before tornadogenesis, the supercell had dropped at least five-inch diameter hail N of Piedmont! Fortunately, none of the damaging hail hit the vehicle as we bailed SE on OK-3 then S on OK-4. We still were in transit (S on OK-4) during the short-lived, rain-wrapped condensation funnel, which Rich could see to our W from the passenger seat at about 2030 CDT (130Z). We actually didn’t get any photos during the condensation stage due to being mobile. By the time we found a safe pull-off, the tornado was gone.

Tuttle-Newcastle evening supercell

Storm mergers and outflow soon doomed the old mesocyclone area, and a major convective mess took over. In darkening twilight, we continued S on OK-4 past I-40, noticing a storm with a fairly large updraft area to our distant WSW and W. That storm assumed some supercellular characteristics, both visually and on radar, but we admittedly were surprised by unconfirmed media reports of a tornado in the Union City area.

We found a side road W of OK-4, a couple miles N of I-44, and began observing the supercell as it moved over Tuttle. Illuminated in various ways by lightning, town light and twilight, this storm was a beauty! I shot numerous photos as the storm approached, mid-upper level electricity brilliantly illuminating the scene aloft as its striated skirt swirled ever closer.

Hail markers on this storm seemed rather large, so we went to Newcastle (in its path) to find an overhang and observe the hail. By the time the storm reached there, however, it had grown upscale into a mess and merged with other cores, producing mostly heavy rain and small hailstones. Tired from a long chase day (and evening!), the Two Chumps then aborted intercept actions and turned E to Norman, satisfied that we milked this atmospheric regime for all it could offer–except the five-inch ice bombs, of course, which we chose to avoid.