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Storm Chase: April 9, 2008

Unlike our previous chases so far this season, it was difficult to decide whether or not we were going to go out. As could be seen from the 18Z surface obs, the best temperatures, dewpoints, and wind fields were down in central Texas...a 6 hour drive.

The 0-1 km SRH at that time was amazing through that area of Texas. Those values were the highest of all the chases thus far this season.

KFWD launched a special sounding at 18Z, which showed amazing shear profiles in the area. In fact, shear was great all throughout the Oklahoma/Texas region.

At 1:20 pm CDT, the SPC issued a PDS tornado watch for a large area of Texas where the clouds were beginning to clear and a Cu field was developing. Oklahoma was completely socked under elevated convection all day, which was initiated by a lead impulse ahead of the main trough.

Buckey, Craig, and I had a heated discussion about whether or not we should chase. Buckey and I were leaning towards a "yes," but Craig, because he was going to be driving, was understandably reluctant to go. After much debate, we simply could not justify not going given the shear profiles down in Texas. However, we decided to not go all the way to Abilene, TX. In fact, Craig's only condition was, "we're not going to Abilene." The SPC probabilities for tornadoes were rather significant.

On our drive south, we were watching the storms that initiated just west of Abilene, one of which grew to become a substantial supercell. This was a radar scan at 3:59 pm CDT.

At 2115 Z, the visible satellite indicated a nice Cu field south of the storms, but everywhere else around the storms were overcast. On our approach to the supercell from the east, we were driving through light to moderate rain the entire time with only a few breaks.

However, even with the overcast, CINH was decreasing ahead of the storms, and SPC issued a second PDS tornado watch at 3:50 pm CDT.

As we continued westward, at 5:16 pm CDT, there were a few radar volume scans that indicated strong rotation in the supercell that appeared tornadic.

We later found out that a tornado had hit the town of Breckenridge, injuring roughly 15 people, destroying several homes, and flipping over a semi. We eventually caught up with the storm, just shortly after the tornadic circulation weakened on radar. The odd thing was, we could not see any storm structure whatsoever even though we were right in front of the mesocyclone!! Indeed, the stratus coverage that day was overwhelming, and we had to rely on radar more so than visually, which did not sit well with me. The following photo looks like a normal, cloudy day, but this was taken in the inflow notch of the supercell looking towards the circulation!

I was admittedly getting a bit nervous because of the lack of visuals outside the car. Craig, Buckey, and I kept squinting at the clouds to see if there was any hint of a circulation. In addition, the chase terrain was absolutely morbid, with ridges and hills surrounding the road. At the town of Brad, we stepped outside of the car to experience the inflow winds. They were tremendous! I estimated around 40-50 kts at the surface, with stratus clouds that moved at a dizzying speed...getting sucked into an unknown circulation that could not be seen.

We had a momentary "Twister" moment when we saw what looked like a scud-filled wall cloud rising above the hill with some good circulation. I was able to capture this time lapse while holding on to my tripod in the intense wind. Pay attention to the circulation to the right side of the animation.

When we thought the circulation had passed north of our latitude, we cautiously drove a few more hundred feet to the northeast to try to get a better view. However, the radar momentarily showed the lack of a defined circulation. We had to go visual, except there was nothing to see besides stratus racing toward the north-northwest. Then, at 6:03 pm CDT, the new volume scan came in, and it appeared that the mesocyclone had redeveloped to our west just ahead of the RFD!



However, it could have just been that the main outbound portion of the mesocyclone was not being properly detected by the radar. In any case, I realized we were in a potentially dangerous position. I looked up at the turbulent skies from the windshield, then yelled, "STOP! BACK UP!" Craig did an amazing three-point turn, and we headed back to the town of Brad less than half a mile back toward the southwest. Once we determined that the storm was racing out ahead of us, we retraced our path from ealier and drove back east. We attempted several intercepts of the storm, but each time we would, would were only given roughly a minute before the clear-slot RFD would come towards us.

The storm was moving with a forward motion of over 40 mph! At one point, there was chaser convergence at the side of the road, but everyone (including the news stations) was looking at the wrong part of the storm! They were looking at the scud on the leading edge of the RFD!

We ignored everyone and proceeded to try and catch the storm near Decatur, TX. We were due south of the updraft of the storm at 7:20 pm CDT, but we had a hard time catching up to it.



As we got closer, I caught a momentary glimpse of what looked like the updraft region of the storm as we raced toward Decatur, but that could have also just been my imagination.

Darkness was overtaking the region, and our time to chase was quickly drawing to a close. We drove through Decatur, just barely clipping the RFD. There was no hail, but we saw reports of tennis ball sized hail in Decatur just before we drove through. Afterwards, we made our way to Denton, TX, paralleling the storm's trajectory traveling to the east. We had a good lightning show, but the storm was not becoming any more tornadic with time, so we set our GPS to a Denny's restaurant in Denton (we've had a hankering for Denny's since our last chase), and had a nice, hearty dinner before continueing home for the night.

Moisture was obviously not a problem today, but visibility certainly was. I was quite surprised by how long the supercell could sustain itself given all the rain-cooled air it was moving into. However, I suppose the dynamically-induced vertical perturbation pressure gradients were enough for it to overcome the lack of surface heating.