Saturday, October 23, 2010

Interesting Null tornado event

The tornado watch appeared promising. Plenty of shear with a bulk wind difference near 25 m s-1, CAPE was solid at 1000-1500 J kg-1 and storms had initiated in proximity to the dry line outflow boundary intersection. The storms stayed small and very early on began to split with small left movers that dissipated rapidly north of the outflow boundary.

Yet, despite having supercell like qualities they faded into obscurity after 2-3 hours.


Missing from the closest observed sounding (taken AFTER the storms and somewhat well removed from the INITIAL area, but was later just south of an area of again small storms) was a layer of steep lapse rates, and a cap. Seemingly the near isothermal area around 500 hPa was a CAPE robber.

This sounding is intriguing only when we look at the overall 12 hour changes  in the area of interest. The 850, 700, 500 temperatures had cooled at OUN. At FWD, 850 and 700 T was down 1 degree C, but the 500 T had warmed by 3 C while at 601 T had cooled by 2.6C! The upper low which showed a jetlet rounding the base of the trough at 500 hPa had weakened by 5 m s-1.

Water vapor imagery doesn't show this 500-600 presumed frontal zone as the upper levels were quite moist. It appears a subtropical jet/ shortwave was influencing the action over Texas.  Maybe this "front" was a small scale circulation. I found it about the same pressure level, same potential temperature at DRT 12 hours prior albeit weaker.

Nothing at the surface really jumps out. Dew points held in the 59-62 F range  in advance of the storms. Something mesoscale was happening for sure but its difficult to understand what. Model simulations anyone?

Sidenote: I did happen to see a wave-like feature that had passed over the CI area just prior to CI on IR imagery that interacted with some small storms in OK. Easily seen on Visible as cirrus.