June 17, 2016

Team Woodchuck's Forecast:

"OK, I’m in for the eastern target. Plan to depart BIS in next 15 mins bound for the Aberdeen-Sisseton-Watertown SD area. The deciding factor for me is the outflow boundary for the overnight MCS up this way. This should provide a well defined focus for initiation in the presence of large CAPE with a formidable cap. With backed flow north of the boundary, conditions might just support low-level rotation, especially early on before cells merge into a mauling MCS. The upper air flow in this area ranks as the weakest for any target I have ever chased, so the low-levels mean everything today if we are to find a tornado. I also note prospects for ~105 F temperatures in SE South Dakota this afternoon, so I am less interested in option further south of my target area.

The E/SE Wyoming target is certainly of interest, and I am fighting my strong bias to head that way. I am just not convinced that dewpoints will recover in time to take advantage of the better shear profile. So, a high based hailing supercell looks very likely, but tornado prospects seem a bit too limited as of now to warrant the 8-9 hour drive.

That’s how I see things as of now. The distance between targets require that we commit to one or the other, with no room to hedge. So, damn the torpedoes, we’re heading east!"

Team Duck's Forecast:

"Day 1: Bifocal target - in the eastern SD area/MN there looks to be rather likely development of storms, however, shear will be relatively marginal, with max values of 20-30 knots deep layer for much of the domain. NAM takes this to infer that it will all grow rather messy and upscale quickly, however, there is still a likelihood of at least some embedded or initially discrete rotating storms, particularly given some degree of a decent low level hodograph despite lacking upper level support. Farther west, there looks to be potential for more isolated storms in a stronger shear environment in response to an approaching shortwave over northeastern WY/SE Montana. NAM here breaks out a few supercells, though updraft helicity tracks are weaker than I would hope to see, likely in relation to reduced LL hodographs. HRRR builds an MCS off the outflow boundary from the overnight/morning convection, which heads southwards, while being slightly less optimistic for the western target core strength, but instead developing some rather intense updraft helicity tracks, particularly along the WY/MT border from the Big Horn Mountains.

My personal suggestion would be the western option, which leaves you in play for tomorrow, just given the better prospects for discrete storms and equal tornado chance, but I would also have a close look at the eastern OFB to see if what its laid down has any shot at producing something interesting.

Day 2: Will it fire in the US or won’t it? Supercells will likely form as the initial mode over northern MT and thus pose a tornado risk given the favorable parameter space, particularly off the high terrain, and track ENE along the international border. Upscale growth with time is expected, likely leading to an eastward propagating MCS that tags the border all the way to eastern ND.

Day 3: Looks to be somewhere in MN/SD, with the shortwave providing ample shear for organized rotating storms, and enough forcing to jump the cap, probably before upscale growth. I would be thinking a target around Mitchell/ Sioux Falls/Willmar corridor as a starting point. "

Intercepting developing line of storms on the South Dakota/Minnesota border, already quickly transitioning into an outflow dominant line.

The gust front hits with a blast of outflow winds, probably reachign 40 to 50 mph.

The northern cells lined out solidly and had a near zero chance of producing photogenic tornadoes for us. New cells were popping up south of Sioux Falls, so we made our back to I-29 heading south. The updraft base of a rapidly organizing cell came into view, but it was caught in the wake of an earlier MCS and so would probably remain high based and partially elevated in the already worked over air.

The storm was cranking out cloud to ground lightning bolts, however.

The striated bands formed overhead and moved with rapid motion.

We moved a few miles south to duck out of the encroaching core. The storms were gusting out hard, however. A small dust storm started to kick up all around us.

This was our last chase with Anton, Tracie, and Tim for the 2016 season as their time on the Plains was up. The howling dust storm hit with some light rain. Light fading and surrounded by outflow dominant storms, the chase was over. We said our goodbyes huddled beneath the hatch of their minivan, braced against the storm.

We got a room at the Super 8 in Aberdeen, close to where Brindley and I would be chasing by ourselves the following couple days before heading home too.