July 4, 2020

Team email forecast discussions:

"Models in general agreement on scenario I think, but vary in placement and storm evolution. Focal point for afternoon and evening supercells appears to be at the top of a CAPE plume with some forcing coming from a weak cold front. Pattern is better defined on NAM, with HRRR looking more mediocre at the surface. But I'm hoping that instead means a more discrete storm mode. LSI and 3Cape support strong surface based updrafts, so no gripes from Turtle there. Limiting factor might be low level flow and directional shear. But both models initiate supercell structures. Placement appears to be highly dependent on overnight and morning storm evolution, with NAM's instability suppressed to the south and lightning up Jamestown by 22z. HRRR is to the northeast closer to Grand Forks and a tad later I believe. Regardless, heading east down the 94 should get us going in the right direction, from which we can refine in the morning when the picture is clearer with what morning storms are doing. Disclaimers: Turtle in full zombie mode, may be overlooking other plays. "

Update:

"Thank you for the detailed analysis, Woodchuck. Turtle concurs and picked an "x marks the spot" between Steele and Jamestown. Dry punch pushing northeast into North Dakota looks to be the focal point, with storms initiating off the nose of the steep low level lapse rate finger. Surface winds back to southeast ahead of this feature, a modest southerly low level jet may be crucial for our chances today, and then light westerly to even northwesterly flow aloft depending on these subtle 500 mb impulses. Low level thermodynamics look very favorable right on the X, points east and south with a lid strength going into the negatives and 3Cape > 100 J/kg. Both would support robust low level updrafts. Turtle noted that HRRR is indicating a northwest shear vector. We may see mesos wrapping up on the west flank of the storm if that's the case. Given that the evening sun is in the northwest sky this time of year, that could yield some very photogenic lighting for us on the back end, not unlike last night. Working against that is storm mode. The back end might not be open for viewing, however, and we'd instead be relying on these angles for strong backlighting chasing from a southeastangle. Flow looks modest at all levels except maybe that 850 mb region when the low level jet perks up in the evening. PWATs at about 1.8 where the best moisture convergene is, coupled with modest venting, so I agree it's an HP mode. Unfortunately, I don't see a quick tube unless some vorticity stretching occurs right off the bat in the high CAPE air. I'd suggest we're at our perch at initiation just in case that happens, as storm motion should be more than manageable, not requiring us to setup downstream. Instead of a quick tube at initiation, the storm may need an hour or two to fully get its act together as it chews on modest 0-1km SRH to ramp up that meso. By then the storm may be fully entrenched in its HP mode. But more subtle lifting mechanism, and point targets rather than than a large linear boundary or areal region, would favor a discrete or isolated storm mode. So storms may indeed be able to take their time pulling it together. NAM NEST hints that at least a couple of cells will go up initially. And that's where my parameter geek powers end, and hopefully Tumbleweed's magic cell picking superpowers can take over. Woodchuck picked the best beach for today's surfing, Turtle says we might get wet, and Tumbleweed knows how and which wave for us to ride! "

Initial action in North Dakota had separation issues and was putting down large cold pools. We wound up chasing congealing cells and gust fronts with dust plumes for a bit. Then we dove south for more discrete storms firing toward the South Dakota border. That's when we got our supercell play, featuring a rotating wall cloud in shades of sea green and yellow with prolific cloud to ground lightning.

We followed the storm south, stopping several times to watch structure and lightning. The CG bolts were continuous in the high dewpoint air.

We turned west out of Westport toward Wetonka and stopped after a couple miles with a full view of the supercell. A southeast moving EF3 tornado was in progress, but we were unaware of it due to it being completely rain wrapped within the HP storm. We watched mid and low level rotation for a few minutes before having to continue south down 281 again as rain from the forward flank encroached.

The storm gusted out and we stopped a couple times to shoot structure before finally letting the gust front overrun us.

The outflow was cool and refreshing. We hung out for awhile enjoying the storm before we all said our goodbyes and the group disbanded for the season.

The drive to Watertown for the night was super pretty with a fiery orange sunset, yellow full moon rising, and small, distant fireworks displays from the isolated farmsteads.

A schematic analysis of the storm that produced the Wetonka EF3.