The Spencer SD Tornado of 30 May 1998

Roger Edwards' storm intercept account


Spencer SD Area Supercells and Tornado of 30 May 98: Forecast and Intercept Strategy

By Roger Edwards

Steve Marks and I had intercepted some high-based, low-precipiation (LP) storms on May 29 near Chadron NE (CDR). Isolated severe thunderstorms also formed after dark SW of CDR, which we watched from our motel in CDR as they produced marginally severe hail S-SE of town. We knew there would be even better potential for supercells the next day somewhere across the northeast NE/southeast SD/northwest IA area based on forecast guidance we had seen two days before in Norman OK, May 29 in North Platte, and that evening via Steve's laptop computer.

Shortly after awakening the next morning in CDR, we noticed on the Weather Channel that strong to severe convection was already underway across north-central NE -- and was already laying down a quasi-zonal outflow boundary. [This stuff appeared to be an extension of the storms we were watching to our S the night before.] A dense plume of cirrostratus was evident on the satellite pictures also, streaming off the central Rockies; and it had a sharp northern edge near the NE/SD border. Immediate concerns, even before downloading more detailed data:

  1. Would the boundary survive the day, and if so...
  2. Where would it be (especially with respect to the cirrostratus pall, which could slow heating), and...
  3. How strong would it be? Strong and vorticity-rich enough to support afternoon supercells on its own, or just strong enough to interfere with inflow to SD dryline or frontal storms? If the later, we would rather it just go away!

Downloading and analyzing surface and upper air data didn't help us a lot to answer those questions, but at least allowed us to confirm what existed and where: a surface low moving E across central SD, warm front eastward to SW MN, cold front extending SW to near us, and a dryline just to our E. Our preliminary forecast was for the boundary to erode from the W with heating, mixing and warm advection (but how far?), the low to be over east-central SD near Mitchell (MHE) or Huron (HON) by 00Z, the dryline to trail SSW from the low, the warm front drifting N over east-central SD near Brookings (BKX) or Watertown (ATY), and a cold front roaring into southern SD from the NW. In those we were fairly confident. If the boundary washed out, east-central or SE SD -- just SE of the surface low -- would be he best place to go in order to target either triple point/warm front storms (if the cap to the S was too strong) or dryline convection (if the cap wasn't). The cap, cirrostratus edge position and outflow boundary were the wild cards!

We left CDR at about 9 a.m., intending to stop at Valentine (VTN) to download more surface and satellite data, and to watch for visual signs of outflow boundary evolution along the way. I had never been through the northern Sand Hills before. What a lonesome, starkly beautiful stretch of countryside: grassy but treeless, stabilized Ice Age dunes as far as the eye could see, whose tops blended together above road level to make us feel as if we were in an endless basin of sand. With the dunes always higher than road level and major roads only every 40-70 miles, what horrible storm intercept country this would be! We were glad the target area was much farther away.

When arriving in VTN, we were obviously on the grungy side of the outflow boundary, with fuzzy broken stratocumulus moving little. If this didn't break soon, we would have to hang out nearby and wait for the front and dryline to crash into the outflow, hoping for help from limited heating under the cirrostratus and enough convergence to pop the stout cap. I didn't want to deal with storms in no-road's land. But while lunching and downloading data at an AmeriPride truck stop, the stratocu broke up fast, giving way to clean skies under the cirrostratus deck. Small cumulus began to form and move northward -- the outflow was dissipating! We could now concentrate more on the larger-scale features up in SD, N of the nasty cirrostratus plume. Also, we noted a strong and persistent thunderstorm Pierre (PIR) along the cold front -- and behind the dryline -- charging ESE. What would this storm or its anvil remains do? We left VTN about 1:30 pm.

On the way N toward Chamberlain (CHB), the good news was leaving the dreaded cirrostratus canopy and watching increased cumulus organization near the dryline. The bad news: we hit hole after hole on a profusely cratered stretch of SD-49, busting the muffler and tailpipe on the Meatwagon. After dragging the muffler on the road for 30-40 miles to CHB, we found a clothes hanger and tied the scraped-up remains of the exhaust system back to the frame, the proceeded loudly east on I-90 to MHE. [For a map of our intercept route from this point on, click here.] We were E of the dryline, but not far; and we wanted to get more E of the surface low. After eating some more and downloading some surface data, we zigzagged up to BKX to be in the best position to play warm front or triple-point development, while still being able to pursue dryline storms to the SW if the cap would allow.

Gassing up at BKX, we noticed an anvil explode to our W, north of Mitchell. It streamed rapidly overhead. It had to be near the triple- point, where vertical shear, isallobaric forcing, low level convergence and lift would be peaked. Intercept mode! But heading W past Volga, we saw the storm had no updraft left, and that it was dying. Other towers were erupting behind it and along the warm front. While we stopped at a lake crossing N of Madison, the line of towers quickly accreted into a stout squall line. Knowing convection would have to have a sharp southern edge given the strong cap to our SW, we decided the best sustained supercell potential was with "tail-end Charlie," and headed for the southernmost anvil-producing region we could see, somewhere near SD-34 between HON-MHE. On the way there, we had to navigate at under 45 mph a horrible 13-mile stretch of US-81 which was entirely gravel! A gravel US highway!?!? SD roads were extremely disappointing, to put it mildly.

Continuing W on SD 34 off US 81, the road improved to concrete (!) and we were able to cruise through anvil rain W toward the updraft base of the tail-end storm, becoming visible above the horizon. We heard severe thunderstorm warnings for storms farther up the line -- then as the wall cloud came into view, a tornado warning for our storm. Encouraged that this updraft at least must have a deep mesocyclone for there to be a warning, we headed W to a spot just W of Artesian. While pulling over, we noticed two important things: a big shower to our SSW which was starting to rain hard on us, and a sharply defined, narrow funnel cloud dangling from the rotating wall cloud to our NNW. The funnel disappeared before we could get out and shoot stills or video; and the wall cloud began to get ragged and disorganized while sucking in rain-cooled air from this annoying shower.

Our tail-end supercell was fast becoming outflow-dominant, and the shower was blocking our view in all other directions but W. As a result, we didn't know for a number of critical minutes that there was a big supercell exploding into the Dakota skies to our SSW. As the shower moved SE and weakened, we saw huge, white, hard, sunlit towers through the clouds to our S: the NW flank of another storm! The old tail-end storm was sending out a raging gust front; and we had to get SE fast before the outflow crashed into the big "new" storm to our S.

It was after 8 pm CDT and we had two choices: abandon intercept operations or drive through the NW side of the storm to our S near MHE (the future Spencer supercell). Zigzagging S and E, we drove through dense rain and E-NE winds, and (at most) occasional pea-size hail. With such puny hail, we figured the storm wasn't too intense yet. WRONG! Driving S on SD25 between Epiphany and Farmer, the rain thinned; and we saw a fuzzy, wide gray column connecting cloud and ground just E of the road, to our SSE. What the heck? We should have begun filming, but didn't in the course of trying to figure out whether this big gray mass we saw through the rain was a large tornado or just a dense precip shaft. It had very smooth, vertical edges; and we were still a little to far into the rain to discern rotation.

After getting into thinner "atomized" rain near the NW rim of the mesocyclone, it became clear: this was a big tornado; and it was cruising ESE away from us. [No video was being shot at the time; I was driving and Steve was on his 2-meter radio. But here is a pencil sketch of the tornado at this time from our vantage, looking SSE on SD 25 from about 3 miles S of Epiphany.] Steve tried to hail someone -- anyone! -- on his 2-meter radio, to advise of the emergency, but to no avail. Driving around an overturned stock trailer and downed power lines on the W side of road, and concentrating on the large tornado churning away to our ESE, we failed to notice the destroyed farmstead just to our right. We were where the tornado had been just minutes before. We finally got out of the rain enough to stop and briefly film the tornado before it got wrapped up in rain and dust. Unable to get out and use the tripod with all the close lightning around, I managed to get just one clear shot braced by the car door, at 1/8 sec through a fully open, fully widened F3.5 28-80 mm lens. We didn't know at the time that the "wedge" tornado was ravaging Spencer, causing F4 damage and killing six elderly people.

We attempted to go east and south in order to get ahead of the mesocyclone, which we knew to contain a big tornado and which we knew was moving hard right. In the process, we got caught in part of the wrap-around hook of heavy rain, and could not see the new storm (and its tornadoes), which had formed to the SW on the virticity-rich rear-flank gust front of the Spencer storm. We saw a suspicious lowering after dark to our NE, occasionally illuminated by lightning. This lowering was smooth, tapered and most of the way to the ground; and it corresponded well to the time and location of tornado number 5 on Brian Smith's path map. Without hard evidence, though, we can't claim it was certainly that tornado. The storm was becoming outflow-dominant and it was getting very dark; so we cut off intercept operations. After getting to a motel north of Sioux City, we called the Sioux Falls NWS office and relayed our reports to MIC Greg Harmon, who welcomed our reports and invited us to assist with the next day's damage survey.

After over 13 years and around 200 storm intercept trips, this was my first violent tornado, and first killer tornado. The latter is rightfully sobering; but as a dedicated storm observer, I realize that humans have no control over where a tornado goes and what it hits. We can only spot and track the storms, documenting them for warning and verification purposes, education of self and others, scientific analysis and photography. The paradox here is that, had the tornado not hit Spencer, it probably would not have been rated F4. It is better, however, to have an under-rated tornado than the death, injury and personal horror that the survivors must forever recount wherever thunderclouds gather. I share the constant wish of most storm observers that tornadoes stay in open country and away from towns and homes. I also realize that these things do happen, and that meteorologists, storm spotters and the general public must be prepared to deal with them. NOTE: The same issues and conflicts would arise again -- on an even larger and more morbid scale -- about 11 months later when I intercepted the Central Oklahoma Outbreak of 3 May 1999.


Additional maps and pictures from slides and/or video captures may be included as time permits.


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