Sandhills Supercellular Struggles and Splendor

August 6, 2007 by
Filed under: Summary 

Hyannis to Ogallala NE, 11 Jun 2007

A long swath of western South Dakota and Nebraska — even down into NE Colorado, looked like it carried the potential for supercells on this afternoon, and I was wandering up and down the dryline with my preferred target area all morning. Ultimately I had to make a basic N-S decision, and I chose S, despite the prospect that storms could form and/or track into the western Sandhills. This was because of richer moisture and somewhat better potential storm-relative inflow in SW or W-central Nebraska. Still, the vacillation continued…but upon exiting the motel, I took one last look at the sfc map and chose a course WSW across the Sandhills, toward the prospective intersection of the (southern) moist axis and the dryline — near MHN.

The plan was to cruise W on NE-12 to VTN, look at updated data at the VTN library, then if not diverted by something really convincing, proceed S and W toward the MHN area. A serene late morning and midday drive ensued across the wetlands E of Niobrara, and the rolling plains between there and Naper. At Naper we had a cheap, greasy and unsatisfying lunch at the local cafe. [At least I was glad to be wearing an OU Sooner shirt there and all across Nebraska on this day!]

Rolling toward VTN on NE-12, we noticed towers going up distant W-WNW — apparently behind the dryline and in the southern part of the Black Hills. A likely dryline (turkey) tower could be seen far, far away to the SW, so many miles away it seemed lunar in distance. While in the VTN library, we noticed the line of towers that extended from near the dryline/moist axis intersection W of MHN, SW across east CO. That was the target area!

Upon leaving VTN we saw new, deep towers W of VTN that were closer (and that would develop into a storm complex along the NE/SD border). Nonetheless, we chose to stick to the forecast, plow along two cross-sections of the Sandhills and go after the storm that eventually developed from that clump of TCu and turkey towers W of MHN. Wheeling S then W through Thedford, the intermittent glimpses afforded by the dunes revealed the largest, darkest area of convection S of NE Highway 2, and a smaller anvil canopy just N of the road. Both cumulonimbi were well separated from the big area of storms farther S, in NE CO and the IML/OGA region, and would remain so. We had the discrete young supercells we wanted, but curse those Sandhills for viewing them!

Because the roads in the Sandhills follow valleys, you’re almost never above surrounding terrain. Even when cresting hills, you’re still lower than nearly all nearby dune ridges. This was a long-known hassle of chasing in those parts, but still, an irritant no less. We had intermittent views of the base of the northern (smaller) storm N of NE-2, and it had a small wall cloud and miniature forward-flank precip area for about 30 minutes before stringing out into oblivion. Them there was one! By process of elimination, our intercept target narrowed.

The same sickly fate wouldn’t meet the southern storm, which was drifting NNE across a vast roadless area WSW of Hyannis. We weren’t confident in finding a viewing spot along NE-2 W of Hyannis, so we turned S to a point 15 S of town where the dunes to the W were at least low enough above the horizon to see some of the area under the storm’s bottom (wide angle). That was the closes we could get, at least without a helicopter or an Abrams tank!

A broad rain-free updraft base and anvil field made for nice, classical, and distant (Crowtheresque) structure shots. Meanwhile, a crisp mammatus field streaming ENE from the storm yielded even better photography, looking in wide-angle views (vertical and horizontal several minutes apart) down a long ribbon of highway to the next dune crest.

I didn’t fire up “NetThreat” until we already had been sitting at that vantage for a spell, and even then, mainly out of curiosity about my storm’s radar structure, or at least that which can be inferred from what Rich T refers to as “cartoon radar” in Baron’s oversmoothed composite reflectivity presentation. Even at that resolution, a fairly well defined hook had begun to protrude S of the main core during the visual appearance of fairly precip-free, robust, tiered updraft. Then, as if on cue and within 10-15 minutes, the storm developed a good deal of precip around the N and W side of the heretofore rain-free base (wide-angle view), and another shallow wall cloud developed with more obvious cloud-base rotation (as seen through zoom lenses and binoculars…yes, binoculars).

Within a few minutes more, around 1758 CDT, a distinctive, rotating lowering (contrast-enhanced zoom) developed from two or three chunks of scud orbiting a common vertical axis, below that wall cloud. It persisted for 3-4 minutes while we prepared to find a better view. This possibly tornadic lowering got smoother and more symmetric, continued to rotate, and extended below the top of the dune line to our W (wide angle shot). It was in about the right location in a storm-relative sense. But because of the terrain’s truculent truncation of our view, we had no way to provide certain confirmation or refutation of what may have been going on beneath.

Was this (see highly enhanced crop) a tornado or not? Given where we were and where it probably was (scrubby dune fields somewhere over eastern Garden County or southwestern Grant County), the answer may never be known.

During our trek back N, brief glances at the base revealed the lowering went away, and the storm was filling in with more rain. Meanwhile WxWorx was showing the structure getting messier; and a string of very high based, initially not surface-rooted convection that developed E of the storm was hurling both raindrops and CGs down around us. Yecch! But the ugly duckling soon would metamorphose into a beautiful swan.

We found another vantage on the Evans Ranch road just N of Hyannis, whereupon a visual delight unfolded. A new storm developed just to our E from that initially elevated string-cheese, and intensified into a greenish, elliptical and high-based HP. For half an hour or more, sinuous strands and ribbons of laminar cloud material surrounded the core and painted a picturesque, otherwordly blend of colors and textures over those grassy green dunes (looking SW and looking NW). The funky cloud displays continued as the storm retrograded toward the NNW at a rate faster than the slow advance of its gust front. The net effect was fascinating too: The gust front was moving out of the storm and in our direction, while retreating away from us! Out of many hundreds of storm intercepts in over 20 years, I can’t recall experiencing that before.

Once that storm backed farther away and weakened, we headed S toward food and lodging in OGA. In the way stood a severe storm anchored by a potent looking updraft, but it quickly shriveled as the bigger complex farther S (in northern CO) grew upscale. Here’s a shot of the final “chicken neck” stage of that updraft, seeming to rise like a geyser from the muscular landscape of the Sandhills’ shortgrass prairie.

No longer impeded by the intervening storm, we cruised S through the Arthur area toward the back side of the burgeoning MCS, stopping at a couple of points N of the McConaughy dam to watch, photograph and appreciate a rainbow beyond wildflowers, a scrambled-egg sky to the S just before sunset (Lake McConaughy is in the far background), and then, gently cloud-filtered sunset colors to the SE and to the SW.

We checked into our motel at OGA, then a late, fast-food meal before discovering that the day’s action wasn’t finished! Some new storms developed along the NW edge of the MCS, to our SW, then rolled toward us. Getting a few shots of their CGs behind the water tower of Ogallala, which is spotlit at night and decorated like ET’s alien vessel, was icing on the cake (shhh…here’s my favorite). Add to that the ongoing deluge and show of CGs and crawlers as I typed much of this summary around midnight that night — in the N rim of a flood producing MCS between OGA, LBF and IML. This capped off a chase day that was frustrating at times but far more enjoyable than not in the end.

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