Thursday, April 30, 2009

Cedar Hill, TX Tornadoes - 29 April 2009

 This turned out to be quite an eventful day. Our main goal was to test out the mobile mesonet software that I've been working on all winter, but we got to see and collect data near tornadoes. We met up with the rest of the group in Plainview, TX at 2pm targeting storms that would fire on the dryline and move off and interact with an outflow boundary from early day convection to the east. A storm fired on the dryline as expected and it slowly moved towards our location throughout the afternoon. We sat at Chubby's BBQ in Plainview for a few hours, had some amazing West Texas BBQ, and watched as our storm slowly gained strength. While it was west of Plainview, the storm had a high base as it's inflow environment was about 85/55. A mid level mesocylone was apparent on radar as the storm approached our location. Our group left Plainview and got east of the storm while it become outflow dominant and took on HP characteristics. It cycled and a new wall cloud formed with a lower base shortly after while the storm began to take on more of a classic supercell character. At this stage there were many gustnadoes along the RFD boundary and even a organized anticyclonic whirl developed on the south end of the storm. The 2nd cycle was uneventful other than dust whirls and a nice wall cloud. At this point it appears that RDF boundary from our supercell surged ahead because it was rather cold and negatively buoyant and I believe this interacted with the outflow boundary from earlier in the day. Just to the south and east of our location, a large, low, dark rain free base quickly developed. The structure was amazing with rapid inflow from the east. We quickly found ourselves in the forward flank downdraft region of the new dominate cell. A few large (1.5") hail stones fell at our location. We quickly drove south to get in front of the "main show". I noticed some rapid downward motion and a "waterfall" effect in the clouds to our south and west. An RFD dry slot quickly developed and cut in what appeared to be from the south and southeast. Within minutes, a rope like "needle" tornado quickly formed and dissipated. Then minutes later the main tornado developed and took on a cone-like appearance for a while with a little bit of dust being kicked up below. The main tornado became a slender cone and condensation descended to the surface.  Our group traveled towards the tornado trying to get in it's path. We sample data within the forward flank downdraft all the way to about 1/2 to 1/4 of a mile north of the tornado as it roped out. We now noticed a new tornado developed maybe a mile or less to our east. As the main tornado crossed the road in front of us just to our south, we were going to get right up behind it to sample data, but the tornado showed a bit of erratic motion so we backed off and stayed about 1/4 mile away. Both tornadoes dissipated and we noticed new development to our east. The roads we were driving on were dirt and we should not have been out there without 4-wheel drive, but we found ourselves stuck after the hook echo passed over and caused our road to essentially become like cookie dough with 3 inches of cake batter on top. We had a Hummer H3 try to "ram" us out of there from behind, but we slowly slide towards a deep ditch and had to abandon that effort. After hours of trying every "MacGyver-like" method to pull us out of there... including ropes, winches, pulleys, Hummers, and large 4 wheel drive trucks without success we were forced to give up. However, a very kind local farmer saved us by coming out and pulling us 2 miles through the mud with his tractor. We were very appreciative as the sun was setting. This was a very memorable chase and I'd put it up there with my top 3 favorites (Manchester, SD being #1).   

Thursday, April 9, 2009

Moderate Risk for severe weather today KS and OK

Severe thunderstorms including supercells with large hail and tornadoes are possible today over southeastern KS and eastern OK. Storms are starting to fire now on the dryline in north central Oklahoma. Here's a cool 3D image of initiation. I don't think this storm is surviving at the moment, but it's a cool image anyways.