June 20, 2019

From my morning chasecast email discussion:

"Day 1 Today: Looks like a classic bust near Yankton, SD. Height rises, top of the ridge, late season... I've done it a half dozen times and I'm doing it again today goddammit. Primary target is Sioux City, Iowa. Hopefully a storms goes up south of Yankton by mid afternoon in the wake of the morning MCS action. It should track southeast and hopefully toward the warm front and better directional shear across the Missouri River. Last night's runs had a couple of supercells tracking for hours through western Iowa. I've seen those storms on radar and always wanted to chase one. Just this totally discrete supercell with a nice hook, trucking all the way across Iowa and into the night. Sounds nice, but alas it's going to be puffy white cloud or a few failed turkey towers and some elevated showers. Still models show uncapped airmass with 2000+ CAPE in northeast Nebraska, 50 knots of bulk shear on the river, and pretty robust helicity across the river in Iowa. Could be a tornado if a storm can maintain itself in the environment that otherwise doesn't have a lot of lift.

Secondary targets: Play further south and hope the Omaha area initiates where the CAPE is higher. The capping starts to get progressively worse south of 80 so watch out for that.

Play a marginal/conditional target north of Sioux Falls. Narrow instability axis with modest instability, but uncapped and sheared. It might go like yesterday did up in South Dakota with pretty minisupercells that try but are a couple bucks short of a tornado.

Play southeast Montana. Decent moisture pool in the Wyoming basin up into Montana. CAMs have some long track supercells moving east by mid afternoon. Looks like structure in the bag. A tornado would be a nice bonus/srurprise.

Play the upslope further south: Earl's thermodynamic plots say no real significant tornado chances except a landspout or dust whirl. If you're going to play the conventional High Plains targets today, maybe because you're holding out for a big show on Friday... You might try Goshen Co. WY where the low level moisture looks a little bit better."

After a drive from South Dakota down to Pilger, NE, Brindley and I double backed for storms developing just north of Sioux City. Bases were hazy and raining, but there was some rising scud acitivity.

We chased the cells southeast, where modest lift and some lingering inhibition probably made the cells more discrete but also wither away. Cyclonic rotation in the base tightened as one of the cells was stretched in its death knell. It was pretty and going through the motions of supercell tornadogenesis, but it was a long ways off from a real tornado.

Friends and chasers Chuck and Carrie caught up with us as we watched the cells die.

Initiation was occurring tens of miles to our south in western Iowa. We blasted down 29 for the intercept. Convection was robust with pileus caps.

We got in front of the storm just as a wall cloud started to take shape.

The wall cloud beefed up with great contrast and color, but the rotation really wasn't there yet. It was soon blasted apart from outflow and we ducked south and east as the precipitation core encroached.

Looking behind us to the north as the storm cycles with a more menacing looking mesocyclone:

The storm recorganized and formed a new wall cloud, and we watched from the south-southwest with a great vantage.

This time the wall ramped up with some rotation. Sculpted by surges in the inflow and outflow, this is about where it peaked. A tornado shot at this moment would have been exquisite, but it wasn't to be.

This cycle was also blasted apart by outflow a couple minutes later as well.

We tracked southeast with the storm. It was obvious that it was dying, but the storm took on new mesmerizing textures and colors as the evening sun lowered.

We setup for stills and time lapse near a creek in gorgeous yellow evening light, and watched rainbows and dancing rainshafts until we finally called the chase.