May 26, 2017


Initial Target
Storm Intercepts
Byers, CO
Colby, KS 10:08 AM 5/26/2017
Garden City, KS 10:59 PM 5/26/2017
Last Chance, CO
0 mph
Wall Cloud, RFD Clear Slot


Upslope/High Plains supercell chase across eastern Colorado. Targeted Byers to Last Chance for afternoon supercell, intercepting tornado warned supercell near Last Chance. Noted prominent RFD clear slot and scuddy attempts at funnels but no tornado. Tracked storm into Kansas noting HP transition before calling chase and heading to Garden City.

Crew and Equipment

Chase partners: Jennifer Brindley Ubl, Anton Seimon, Tracie Seimon. Equipment: Sony FDR-AX100, Canon 60D with EFS 10-22mm, Canon t2i with EF 50mm.




Team Duck’s (remote) Forecast:

“Surface analysis places a low over northwest OK this morning, with a sagging cold front now becoming diffuse and mixing out stretching from near AMA westwards to Las Vegas, northeastward to Woodward and northwards toward Sioux Falls. While this cold frontal feature continues to slowly progress, lee cyclogenesis is expected today east of the front range, with a new low developing over Pueblo and southern CO. This scenario will place a strong upslope flow scenario, with dewpoints moving into the low 50s (53-55F as far west as Limon depending on if you believe NAM or GFS – my money would be toward the lower end unless storms pre-moisten) coincident with an impulse that will also kick out later in the afternoon over northeast CO from the northern jet stream, and a second axis of development in Southern CO in response to westward surging moisture being approached by a shortwave originating from the southern subtropical jet stream. This second environment into the OK panhandle will be characterized by dewpoints into the mid to upper 60s around the convective maximum.

The northern target looks highly supercell favorable, with winds backing from east to WSW with height and long big loop hodographs as a response, though initially hodographs will be more modest until the low develops somewhat (GFS has some crazy 800 SRH 0-3km, 400 0-1km environment in place that I struggle to believe by late evening, but it looks like upper level weaknesses in the hodograph might result in relatively slow storm motions, but impressive storm relative hodographs.) Its challenging to find a sounding that doesn’t have convective contamination though, so take that for what it is worth – I think the best shot for the northern target would be a starting point near Byers, CO. NAM NEST wants to put a nice discrete supercell up here, tracking eastwards along the interstate with some pretty impressive helicity swathes – not surprising given the environment. Initiation will be typically Coloradian, around 19-20Z. CAPE will be around ~ 1500 J/kg with a net bulk shear of 45-50 knots around initiation, growing to perhaps 2000 J/kg as the evening progresses, with DLS increasing to closer to 60 knots. HRRR favors a similar scenario, though not as intense as the NAM signal, with an eastward propagating supercell along I70. Intriguingly, HRRR also points towards the potential for early tornadic storms in WY – which would fit given the environmental profiles.

A second location favoring initiation will be SE CO near the Black Mesa, a little later at around 21-22Z. Here terrain features again will be the primary source given relatively strong capping, with a surging dryline kicking eastwards under the strong SW flow. Initially storms will be high based in a relatively dry environment, but propagating eastwards will encounter a considerably richer airmass characterized by upper 60s dews. Given solid wind profiles, these should be discrete supercells as well, though they lack as nice turning as the CO play, but will still have tornadic potential, particularly with increasing time toward 00Z and thereafter, as conditions favor LLJ development, increasing moisture availability blowing CAPE into the ~3000 J/kg range increasing hodograph length and STP values into the 2-3 range, contrasting values near 1 in the northern target throughout (though I wouldn’t worry about this in the northern target – 1 STP in CO =/ 1 STP in OK because of its formulation). While NAM favors supercells moving into the OK panhandle, HRRR by contrast forms these cells further into SE CO, tracking eastward through the afternoon as NW OK and the panhandle never moistens quite to the level of NAM.

Blending this guidance – I would advocate for playing the northern CO play as the moisture is less conditional and varied in the guidance and fits with the morning surface analysis, has better shear and if the terrain fails a nice impulse that kicks through to start the show – I would consider starting near Byers, CO and watching for development over the usual spots on the Palmer Divide. Tornadoes should be likely, and condense fully given the 50s dewpoints instead of yesterdays ragged airmass. “

Team Woodchuck’s Forecast:

“I like, though don’t yet love, the tornadic potential for today’s chasing. Supercells are hardly in doubt though, and slower expected storm motions than yesterday are very much welcome. We have very cold 500 mb temperatures (-15 C at Denver this morning) — it is snowing at Pinedale WY this morning), so copious hail should characterize storms again today.

With SE flow returning and a Denver cyclone possible, Turtle and Woodchuck should aim to meet by 1830z/12:30 MDT at Bennett CO just east of Denver. Possible chase targets include the Cheyenne Ridge, Denver-Last Chance, Limon-Kit Carson and Raton Mesa around Springfield onward to Guymon. The cap over OK and TX is about as strong as any (+29 C at 850 at both OUN and FWD), so this should shut down the daytime convective potential there. I suggest we monitor data and CAM model trends before angling one way of the other today. Today’s chess game with the atmosphere should kick off early in the afternoon and keep us occupied for many hours. Fun! Decision-making passes from Skip to me today. “

Team Turtle’s Forecast:

“Remarkable run to run consistency and agreement on the HRRR and and NAM NEST runs with a dominate supercell initiating off our starting point and tracking down highway 36, peaking in the 22-23z time range near Anton, Colorado.

Logistically that might take us out of the running for playing down the line in north Texas on Saturday and force a sc-se KS/nc-ne OK play near initiation before MCS of doom forms. Alternatively, if our storm turns into Gusty McOutflow early tonight and we have strong reason to avoid the wf/cf triple point tomorrow we could call the chase early and start heading for TX.”
Team Duck Forecast:

“16Z hand analysis is attached. Return flow to the DVCZ hasn’t established yet and the moisture axis isn’t the best, but still looks like a decent play for NE CO this afternoon (perhaps a little less so further south). CAM guidance continues to point the way here with nice supercell signatures.

My views for tomorrow are evolving somewhat as well. I’d be watching two other areas – under the upper low and in the wraparound which will be in the OK panhandle/S KS/NW OK. Recent CAM guidance is leading towards igniting something off the Wichita mountains. Based on the pattern, and the fact that it isn’t as late as the MCS initiation I think this could be a valid play in the Wichita’s-Ardmore line in C OK. The CF looks to light up with major MCS later on – but perhaps there will be an opportunity to nail an earlier supercell. It is going to be a tough haul (but I think if you stand a chance anywhere its off the Palmer east/NE of Limon today for a tornado – DIA might get a little busy around initiation with landspouts apu ;)). I’ll keep watching and provide a forecast closer to 00Z to try and provide as much help and guidance as I can.”

Packing Up
2 miles S of Colby, KS
10:00 AM
We started the day under bright, clear skies in Colby, KS hopeful that we were at least going to see some pretty High Plains storms. We packed up the car next to some others chasers that had crashed the same motel.
We met up with Anton and Tracie east of the Denver airport. Fledgling storms were going up overhead, but they needed some time to organize and consolidate first.

Wall Cloud
10 miles NNE of Deer Trail, CO
4:44 PM
Just as the high-resolution models had predicted, and right on cue, we had our target cell. A high based cell started to organize north of highway 36 tracking east. We pursued it from the highway, stopping on a hill and away from the chaser crowded highway to watch it. We were soon joined by Nick Nolte and Brad Goddard. A first attempt at a wall cloud was spotted as smaller cells merged from the south hitting us with a smattering of rain and blowing dust.

RFD Clear Slot
6 miles NE of Last Chance, CO
5:15 PM
The storm organized into a supercell and picked up a tornado warning. We nosed in closer, turning north off the highway onto the unpaved grid. A prominent rear flank downdraft clear slot was visible to the north beneath the classic supercell.

Scud Funnel
6 miles NE of Last Chance, CO
5:20 PM
A lowering rapidly condensed beneath the base, what looked like a scuddy funnel. Our caravan separated a bit to give some spacing for our shots as we deployed hoping to capture a tornado.
The feature wasn’t rotating very strongly, however, and wound up being more of a tease than the beginnings of a tornado.
The backend of the storm made some weak funnel attempts as well, likely just the updraft tubes tightening up as they withered.

Dramatic HP
26 miles SSE of Yuma, CO
6:36 PM
The clear slot structure started to fall apart as the storm drifted off to the east, but we kept up with it as it was the only game in town. Near Joes, CO we turned north to get into the inflow notch. The storm was now in a high precipitation state. Getting a photogenic tornado was less likely, but the storm itself was still very photogenic and dramatic looking.
Brindley spotted the cows.

Cows and Storm
26 miles SSE of Yuma, CO
6:44 PM
The cows congregated to check us out as they worried about the approaching storm. We stayed until the last minute before the hail core hit, the cows would have to endure it.
We tracked the storm all the way into Kansas, but it had peaked between Last Chance and Joes. To get some ground on the next day's target, we headed south down to Garden City for dinner and a room.


We considered the chase a success despite not getting a tornado out of the day. We weren't expecting one given the low expectations and marginal parameters. However, we had scored a dramatic and photogenic supercell that provided some great time lapse sequences, structure, and lightning shots. That made the chase for us. We also got a practice deployment for our research project.

Lessons Learned

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