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Storm Chase: March 26, 2009

Overview: Conditional chase day, due to strong cap. However, with good potential instability, good low-level shear, and friendly storm motions, a chase was warranted. Dryline bulge provided the initial lift to kick off two long-lived supercells, one of which was confirmed to be tornadic. We were close to that circulation, but was not close enough to see the actual tornado. Storm mergers and complicated road network provided a unique challenge.
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Unlike the previous chase on Monday 3/23/09, dynamic forcing was weaker, but thermal instability was greater. Morning cloud cover encompassed most of the target area of the Red River valley near the I-35 corridor, thus leading to questions about whether or not storms could break the cap. Most of the cloud cover was low-level stratus and stratocumulus, but a cirrus canopy from an MCS over coastal southeast TX encroached upon the region as well. Thankfully, the left-exit region of the jet evident in the 12Z 250 mb map pushed east, and the MCS followed suit.

Surface winds were nicely backed all day, leading to favorable directional shear in the low-levels. The magnitudes could have been better, but if storms could fire, we were convinced that rotation would still be likely. Dewpoints were also promising, with areas in north central TX climbing into the lower 60s by 20Z.

Shear vectors perpendicular to the dryline gave us hope for the discrete nature of storms that do break the cap.

By 2131Z, clearing had advanced rapidly toward the I-35 corridor north of DFW, with insolation pushing temperatures into the upper 70s just ahead of the dryline. Isolated cumulus could be seen along the dryline as well.

While driving south on I-35, Nick, Craig, Steve, and I were all joking about why we even bothered chasing. However, we kept pushing forward despite the conditional probabilities of severe storms. After a brief stop in Denton for some Chex Mix and chips, we pondered the 12Z and 20Z soundings from Dallas. While the cap increased due to warm air advection at 850 mb, the low-level hodographs improved, and the convective temperature was not as high as we had initially expected. Add to that the observed clearing to the west of I-35, and we became much more hopeful for convective initiation before dark.

We sat around doing some radar "blip watching," then decided to go after the new convection that fired on the dryline bulge evident in the KFDR base reflectivity at 4:42 pm CDT.

The red river proved to be a pain, so we crossed it...just to have it die on us.