Daytime Mild, Evening Wild

May 17, 2009 by · 2 Comments
Filed under: Summary 

Hennessey to Anadarko and Norman
13 May 9

SHORT: Observed multicells and supercells before dark from W of Hennessey to SW of Calumet. Witnessed Gracemont-Anadarko night supercell and power flashes from tornado and RFD winds. Observed part of separate supercell E of Norman after earlier tornado.

LONG: Given the very strong capping that was forecast, and the increasing uncertainty of diurnal storm initiation with southward extent, Elke and I targeted a conceptual zone just NE of the projected “anchor area” of a front-dryline intersection zone. The plan was to grab storms discretely backbuilding SW down the front and watch them in stair-step fashion, until either they lined out or became less interesting than newer development. Once, again, confidence in cap strength gave us the luxury of a late lunch in Norman, before we headed up to Kingfisher. Storms fired to our NNE near the KS border (one of them being the briefly tornadic event that Joel and Blufie captured on the way W from TUL…great work, dudes!). We briefly considered that activity, but turned our attention to newer cells visibly erupting into the sky over Major County, NW of town.

When we arrived at a decent viewing spot between Hennessey and Okeene, the bases looked rather flat and linear, as if frontally forced; but the then-anchor storm got better organized, with a nice anvil push with mammatus, and some tail cloud development off the NE side. ESE storm movement and CGs chased us from the spot. We headed S — coincidentally on the same paved back road W and SW of Hennessey from which we photographed a spectacularly unplanned “planned burn” earlier this season. Other smaller cells started to develop farther SW, merging into the complex, and contributing to a hard net right turn and SSE motion that had us zig-zagging on some paved, but at times quite rough, unmarked roads from Kingfisher SW to Calumet, keeping within viewing distance of the storms now pounding areas around Watonga and Geary.

The daylight was getting short and the low-level jet began to crank up, so we had some hope for more convincing supercellular structure. After exiting Calumet, those hopes came to fruition. On the NE side of the newer cluster of storms to our W (the same one under which Kiel O and KMan observed the landspout up close), a bonafide supercell formed and quickly developed a very low-hanging, slowly rotating wall cloud (wide angle and zoom).

We headed over I-40 S of Calumet, faced with either a 32-mile detour E, S then W on good roads, but with little daylight left, or 4 miles of thinly graveled dirt road leading to to an unmarked paved byway headed S toward Cogar with a bridge over the Canadian River. I chose the latter; and the “crappy” road actually was friendlier to my car than the many more miles of paved but horrendously maintained trash we had been traversing between Loyal and Calumet.

Meanwhile, the wall cloud had gotten undercut, but the broader storm began to acquire striations, and assumed a more circular appearance. In the fading twilight, we could make out a more sharply banded, “stacked plates” appearance to the storm while rounding the corner from Cogar to Gracemont, staying just ahead of its hard southward charge.

Here comes some meteorological discussion for the unitiated to skip, if compelled. I figured this laminarity was related to the balance between the storm’s improving organization and the strengthening of both capping and environmental low-level shear. A mixed-layer lifted sounding curve was “capped” in a pure parcel theory sense, and growing more so all the time through gradual diabatic cooling of the near-surface layer. Despite that apparent handicap, the supercell’s strengthening deep mesocyclone and vertical pressure gradient force caused deep ascent of parcels from the boundary layer through the environmental capping inversion. Effective lifted parcels still were bringing near-70 degree dew point air from the surface into this storm, while the LCL was lowering due to cooling temperatures and loss of deep boundary layer mixing. The strong inversion also was keeping the storm cluster rather isolated from a few others farther NE along the front, so it had no “outside competition” or impediment whatsoever for high theta-e source parcels, other than being able to maintain its own inflow-outflow balance. Storm-relative inflow was quite favorable, thanks to the supercell’s deviant SSE to S motion right into the intensifying low-level jet, which also was enlarging the 0-1 KM AGL hodograph and storm-relative helicity quite a bit. As long as the storm could forcibly inhale surface-based air in this window of opportunity (before either losing access to the boundary layer or evolving into a bow echo), it could survive, thrive and perhaps get really dangerous.

OK, that was the end of most of the jargon…

I described all that because it seems to fit a pattern we often see precede tornadoes with very late afternoon supercells that seem rather unproductive by day, then go berserk at or just after dusk. This one did!

I tried to find a vantage between Gracemont and Anadarko to watch the storm coming in from the N. It’s a good thing we didn’t succeed. Instead we turned E out of Anadarko toward a favorite viewing spot of mine — a service driveway for a hilltop broadcast mast located exactly 6 miles E of town, off the N side of Highway 9.

We parked on the big signal hill watching and photographing that (by then) spectacularly sculpted supercell move in, illuminated by lightning. While we were still parked but packing up, and right before the power flashes started, Elke saw some sort of conical downward protuberance to the near right (N) of the eventual location of the flashes, to our W, silhouetted by faint lightning flashes.

Unfortunately, my still camera had been pointed 90 degrees the other way, northward toward that great structure on the storm’s E side and occasional CGs blasting through the vault region. The last shot was three minutes before the Gracemont-Anadarko tornado became indirectly apparent to the W, off the left side of the image.

We had to bail due to encroaching CG activity (that was my widest wide-angle!); otherwise I might have had a photo of a night tornado — or at least, wheeled the tripod head around for to capture its effect of snapping utility lines. As we were pulling out of our parking place, we saw around a dozen bright power flashes in several different spots ~6 miles to the W, within a 3 minute span…in or very near the N side of Anadarko. The flashes appeared to be buried in thick precip, but were quite vivid, displaying a variety of coloration — some blue, some green, some in between, even a couple with reddish and yellow tinges.

Unfortunately, damage obviously was occurring, but we failed in our attempts to report it in real time. Elke wasn’t getting any traffic on her pre-programmed HAM frequencies. [Turns out the net control operator was sustaining damage to his own business there in Anadarko.] I tried to call the 1-800 numbers I had for the WFO but instead got either a recorded message asking me to call a different 1-800 number to “chat with friends nationwide” (for one number) or rapid busy signals (for the other). [I've since gotten updated contact info...thanks Rick for responding so fast!] We then lost all cell signals until we got to the S side of Chickasha, which is very unusual. Finally, somewhere S of CHK on US-81, I was able to call work and ask them to relay the delayed report of the power flashes to the WFO.

We then heard the tornado warnings close to home in Cleveland County, abandoned our (by now) outflow-dominant HP monster SW of Chickasha, and made a beeline back to Norman. We arrived after its weak tornado near Stanley Draper Lake. From Highway 9 east, not far from our house (!), we saw a ragged wall cloud moving SE across the Lake Thunderbird area before it got lost in precip and distance. The lightning show on the back side of the supercell’s HP hook was continuous and dazzling, but mainly in-core. I did capture a few CGs (like this one) looking out my east facing, second-floor window at home.

Based on WFO Norman’s damage survey the next day, an RFD caused most of the damage in Anadarko; but a significant (EF-2) tornado did track from Gracemont southward into parts of Anadarko. This probably was the conical lowering Elke saw right before the power flashes. Here was that part of the WFO report:

    TORNADO – CADDO COUNTY – NEAR GRACEMONT TO ANADARKO
    922PM-940PM
    THIS TORNADO LIKELY DEVELOPED NEAR GRACEMONT AND MOVED SOUTH ALONG
    AND JUST EAST OF HIGHWAY 8. THE MOST SIGNIFICANT DAMAGE WAS NOTED
    ALONG COUNTRY CLUB ROAD IN ANADARKO WHERE SEVERAL HOMES HAD
    SIGNIFICANT DAMAGE. THE PRELIMINARY RATING FOR THIS TORNADO IS
    EF2…ALTHOUGH THIS IS SUBJECT TO CHANGE PENDING FURTHER REVIEW OF
    DATA. MOST OF THE DAMAGE IN ANADARKO WAS LIKELY THE RESULT OF
    STRAIGHT LINE WINDS ASSOCIATED WITH A LARGE REAR FLANK DOWNDRAFT.

Since we were perpendicular to (east of) both the tornado and RFD tracks, I don’t know how many of the flashes were tornadic in origin, and how many were caused by RFD wind. The power flashes illuminated dense precip, and were rain-wrapped. It was sobering and sad to know that people were in danger, unable to communicate about it, and only hoping nobody would get killed or hurt seriously. I’m glad and pleasantly surprised that the Anadarko tornado/RFD damage event didn’t.