Four Supercells Seen from One Spot

November 7, 2008 by · Comments Off on Four Supercells Seen from One Spot
Filed under: Forecast, Summary 

Who Needs to Chase?
5 November 8

Even though I was committed by shift work to being at NWC through the evening hours, there wasn’t any pressing need to chase today to see supercells anyway. All I had to do was pay some intermittent attention to what was going on outside, watch them race by, and run out for a minute or two a few times to observe.

After several storms formed ahead of the west-central OK dryline, and in a narrow plume of favorably heated and moist boundary layer air, a visual treat ensued, which I was able to document in a few quick breaks from the priority of duty.

The first visible supercell moved past me well to the NW (Piedmont/OKC storm) as I drove in, but the sky was clean, and the base could be seen way off in the distance (sorry, no photos). I did see a ragged, scuddy wall cloud just above the horizon before losing sight of the storm. The next supercell moved NE from the CHK area over the W and NW part of Norman, exhibiting classical (if somewhat messy) structure in a wide-angle view, looking W. A zoom view shows a ragged, partly rain-wrapped wall cloud (strongly enhanced image), which showed (at best) very weak cloud-base turning. Upward motion of scud was rather slow too. Still, this storm was a well-defined supercell, visually and on radar, and and dumped a large amount of severe hail in a swath across the NW side of town. The mesocyclone area below cloud base soon became outflow contaminated, a process becoming evident in this view looking NNW.

A second, weaker supercell formed SSW of town, its forward-flank core heading right for us. A left-split updraft tried to calve off the forward (NW) flank of the storm (view looking SW), but didn’t last too long. The back side of the main storm, which passed over E Norman, caught direct and indirect light from the setting sun, and glowed almost otherworldly in pastel hues, making an uncommonly and delightfully tinted scene above the fall colors of local trees. The view in the last shot looks SE, which means that the light was reflected from the storm, casting unusual shadows and light angles for this time of day. Notice that the brightest light is on the left (NE) side of the trees!

The towers responsible for that reflection loom above a mostly silhouetted structure of “Battlestar Norman” in this view, looking ENE from the adjacent lawn. As the sun angle fell further, the hues warmed for just a few minutes (seen here looking ENE from the N side of the building). Even as the reflected solar glow faded, the hues of twilight kept the scene beautiful (wide angle, looking E). Not bad for November, eh?

That wasn’t all. A short while later, Ryan came in to request photography of a feature that looked a lot like a midlevel funnel, apparently sticking sideways (southward) from a convective deck to our WSW (crop-n-zoom on the feature). It was hard to tell if that really was a sideways, midlevel funnel or just a visual juxtaposition of two separated clouds. You make the call.

A well-defined left split peeled off another supercell (unseen) to our S. The anticyclonic supercell raced by us to the W, in the fading twilight, also leaving a swath of hail from the small but pronounced core on its S side. This is a mirror image of the left split showing classic skeletal structure, albeit high-based.

As for the broader event, as a whole and outside the line of sight from the NWC ground floor, it was resoundingly unproductive for tornadoes. All we had were a few cheesy tornado reports long after dark and outside of the 15%_SigTor (MDT) outlook area. What went wrong? My during-and-after interpretation of eyewitness observation, surface maps, soundings and radar inferences was that a blend of storm-scale and boundary layer thermodynamic failures was at least partly responsible. The storms were somewhat high based and spewing a good deal of cold outflow (as well as hail). Mesocyclonic occlusions and transitions to (cold) rain-wrapped states occurred quickly, resulting in insufficient time for circulations to form and wrap up tightly. Supercellular structures did improve during the sunset/twilight periods; but unlike in more moist events, MLCINH also ramped up quickly with enough surface T-Td spread to foment an unfavorable amount of cooling. Discrete supercells — by then E of I-35 — responded by shriveling away as they headed into the jungles of eastern OK.

What might this event have done had the dew points been 5 deg F higher? John H and I speculated on shift that we would have had a more buoyant and temporally longer lasting surface-based effective inflow layer, the better to take advantage of the enlarged hodographs beneath the early evening strengthening of the LLJ, and perhaps a bonafide multi-tornado event in that case. The citizenry of NW Norman should be glad for those lower dew points. Had that storm been tornadic, while still takin the same path (an unlikely thing, admittedly, given the forcing that differing storm-scale processes can exert on a storm’s motion) the path would have gone through some newly (last 10-15 years) developed parts of town W of I-35 and N of Robinson.

We see one sig-hail report from the Piedmont area storm (Rancho Rascovich being a supercell attractor of the highest order). The NW Norman supercell did dump a lot of hail up to nearly 2 inches diameter on several neighborhoods, busting windows and/or skylights in many homes where accompanied by estimated severe gusts, with glass breakage at the homes of several colleagues and co-workers who live in NW Norman. Elke encountered some falling hail ~1.5 inch diameter near and N of the YMCA (north base area) from a small core after dark, near the cold front.

FCST: 12 Mar 6 Eastern KS

March 12, 2006 by · Comments Off on FCST: 12 Mar 6 Eastern KS
Filed under: Forecast 

Today’s potential setup reminds me in some ways of 8 May 3, especially at the sfc, with the warm front retreating N across eastern KS, a vigorous dryline moving E across central/ern KS and central OK upon which storms should fire and quickly become supercells, deep-layer shear so extreme as to be almost *too* strong…and outrageous Warp 4 storm motions that would make the engineers of the Starship Enterprise green with envy. I recall elke and I seeing the second of our couple of tornadoes that day (at LWC) with a formerly robust supercell that, by then, had withered to a skinny and strongly tilted TCu with no anvil and the tornado comprising almost the entire updraft.

SFC analysis shows two warm frontal areas — one moving N across the KS border from PC eastward to MO, one along a GBD-EMP-AIZ line that should merge with the southern warn front later today as the latter moves N. I-70 looks like a reasonable position for the resulting front later this afternoon, say between 22-0Z. Early sfc-based storms may go along the dryline near the sfc low (as on 8 May), get intense really fast, maybe even drop a tube before quickly roaring across the warm front and into oblivion. The more confident play may be for dryline storms forming S of the triple point in the Newton-PNC corridor (or just E of there in the western Flint Hills) and racing NE to tornadic maturity from there. Expect 2000-2500 J/kg sfc-based CAPE (in my area of interest).

Uncertainty for CI diminishes with Nward extent up the dryline toward the triple point because of the proximity to strongest pressure falls and accordingly backed (and convergent) flow. Obviously capping becomes a concern into OK with the EML-from-hell. That said, it would not surprise me *at all* for a rogue supercell or two to fire down the dryline *somewhere* between PNC-ADM, move ENE at, say, *only* warp 2 or 3, and produce a 200 or more mile long string of severe reports per storm, streaking NE into AR and southern MO. Want to make that play? As Clint Eastwood once asked, “Are you feeling lucky”? If the answer is “yes” or even “damn straight I am,” then set up somewhere in EC-NE OK to bullfight such a storm as it matures into tornadic phase.

RLT and I are likely to head through TUL toward SE KS and go from there. The area from CNU-EMP-Ottawa looks really interesting, ahead of what could be a dryline bulge/surge (nose of “dry punch”).

The question today on tornadoes (even SIG tornadoes) is not if, but where and when. It will take mighty good strategy, and maybe a dollop of luck, to be in optimal viewing position given the blistering translational speeds to be attained by storms today.


27 March 2004 – Western OK

March 27, 2004 by · Comments Off on 27 March 2004 – Western OK
Filed under: Forecast 

sfc map


Well, today is only a little clearer than mud, although the reasonable target area is fairly narrow. The near-MAULs and weak cap on the morning AMA/MAF raobs and weak cap indicate that, for discrete storms, it may be an early show, and that we need to get on the road soon. [I say near-MAUL because the UL is not exactly true…those layers had lapse rates weaker than absolutely unstable.]

John Hart’s sounding pageis a great way to look at RAOBS, BTW…in a way more visually appealing to me, and that I can read much easier than the UCAR or COD displays.

Alnado’s sfc map as of 11:10:34 CST shows the dryline/cold front intersection a little NE of GCK, dryline SSW through Beaver County to just W of Canadian, moving E through the Post/Slaton area and already past MAF. The dryline is mixing and advecting nicely off the Caprock, a process which shall continue through the remainder of the afternoon until it crosses into OK. I do see some evidence for a weakly baroclinic and kinematic (wind shift) ENE-WSW boundary, as Bobby mentioned, just S of the Red River, which would lift N through the afternoon.

Examination of the sfc maps show a relative dry hole down in central and west-central TX, with dew points mid-upper 50s F, and which has been advertised by the Eta for several days now. Gripe all you want, justifiably, about that model’s other problems related to severe convective forecasting; but it seems to pick up on these dry holes well. [29 May 1 Kress-Turkey storm was badly assaulted by inflow trajectories from an even more pronounced dry hole.] This is something to watch for the farther S one chooses to play a storm. Therefore I am not inclined to go too far S of the Red River, if at all.

Farther N, generally N of I-40, VIS imagery shows there is a narrower window of optimal diabatic heating between the W side of the pre-drylinear clouds/storms and the dryline itself. It is possible to get a tornadic storm farther N, but lower probability IMO, particlularly with the front rampaging into NW OK later today. Farther S along the dryline in SW OK, the midlevel flow should strengthen and become more westerly with time this afternoon as the main trough impinges upon the area, increasing crossover and absolute 0-6 km AGL shear.

These factors bracket my area down to the CSM-CDS corridor. We’ll head WSW past the Wichita Mountains, and “go visual.”

The hoards will be out. If a few careless, unthinking yahoos leave tripods set up in active traffic lanes, their loss! I do not plan to drive *around* such equipment as in the past. My front end already has some damage, so a little more won’t matter.