June 18, 2009 chase account

I can't say a blue sky cap bust wasn't likely this day, but I honestly was hoping for more. The thermodynamic setup on this day was among the most impressive and insane I have ever seen. Just check out the 00Z sounding from Davenport:

00Z Davenport sounding

Yep, that's right...analyzed 7100 J/kg of surface-based CAPE! Kinematically, the setup was also pretty good. Note the 400 m²/s² 0-1 km, 0-3 km, and effective SRH also! These resulted in insane index values of the supercell composite and SigTor parameters. Yet no convection fired during daylight hours, and when it finally did later in the evening, it was > 100 miles away from Davenport.

The explanation for all of this: very warm and moist conditions worked their way into Iowa during the day, and a morning MCS moving through the area laid down a nice outflow boundary which I was convinced would serve as the focal point for convective initiation. Check out the surface observations at 1800UTC, 2000UTC, 2100UTC. We were talking mid to upper 80s to the low 90s temperatures with mid to upper 70s dewpoints (with scattered 80° readings)! These surface conditions were resulting in RUC analyzed SBCAPE values of over 6000 J/kg! But no storms formed...can you guess why? Yep...cap. Look at the 700 mb temps. The 13°C contour is not included, but I assure you it had overspread most of the state and stuck around until well after 00Z. This was weird because the analyzed SBCAPE field above said most of the state was uncapped, with CIN values less than 25 J/kg.

Nonetheless, I and several ISU students targeted the OFB near Fort Dodge, as an area of enhanced convergence appeared there. But, you already know the end of this story. We sat in Fort Dodge for several hours, watching no decrease in 700 mb temps and a nice cirrus deck roll in early in the evening, pretty much officially precluding storms from forming. I stuck it out until 7, but was having bad feelings at 5. It's too bad, really. With the environmental conditions as they were (minus the cap), a significant severe weather event could have occurred. Not that I want that to happen to people, but it would've been cool to see.

By the way, in case you were wondering why I brought up Davenport's instead of Omaha's sounding, the 00Z KOAX sounding is here. It was less impressive.

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