Chase Notes from 13 April 1996 - by Sam Barricklow The possibility of an afternoon chase was discussed during lunch with other stormchasers, after the annual TESSA meeting. We were all HUNGRY for STORMS! There was potential for severe weather, but moisture was somewhat limited and the cap was strong, as evidenced by a total absence of clouds. As we left the restaurant, I joked that the reason there were no clouds visible to the east was because they were being suppressed by the giant supercell that was out of our view behind the restaurant to the west. We all had hopes that something would develop, but we felt that the cap was too strong over North Texas and moisture too limited farther north in Oklahoma. I went home and downloaded current surface obs. At mid-afternoon, the dry line was just east of a line from Wichita Falls to Abilene. Surface winds were strong across North Texas, the winds were ESE to SE ahead of the dry line and the upper level system looked potent on The Weather Channel satellite motion. (I wish they would show water vapor imagery in motion more often!) A significant temperature difference of 8 to 10 degrees existed between Stephenville/Abilene and the Mineral Wells/DFW areas. There was still a chance storms would develop! Around 5 p.m., the first radar echoes appeared near Graham and slowly intensified as they moved toward Jacksboro. I called Bruce Hanie and we agreed that it was time to chase. As we drove north on I-35 from I-635 in NW Dallas, we could see several anvils to the NW through SW. The anvil northwest of Denton looked the best. It was thick and extended the farthest to the ENE and had a sharp straight southern edge, traits that are typically associated with a storm being fed by a supercell updraft. The next cell south was still developing and had a weaker scalloped southern anvil edge typical of a multi-cell storm. We didn't know then that the southern cell would become the "storm of the day". We felt that we had time to take a look at the northern storm and then drop back ahead of one of the storms developing farther south, if necessary. NWS dopplar radar indicated that the updraft on our northern storm was rotating, but had not exceeded the meso threshold. Visually, the storm was high based with two inflow bands feeding into a small circular LP updraft that appeared to be above the boundary layer. It still produced a vivid lightning show, including numerous anvil crawlers, zits and CGs. (These storms were the most electrically active of any that I have seen in the North Texas so far this Spring.) We watched our northern LP storm for a while as it moved by to the NE. In the mean time, the next storm south had become severe. Michael Cohen, KB5KAR and Bobby Eddins, N5OLO, were about 30 or so miles to our west in Rhome, watching this storm. Mike and Bobby reported that their storm also appeared to be an LP supercell, with a relatively small, but impressive rain-free base. They described the base as being comma shaped, with a wall cloud in the comma head, at the north end of the base. After a warning was issued on the southern storm, Bruce and I left the northern storm and our observing site near Bolivar, NW of Denton and drove south to highway 380 and then southwest to Ponder. When we were just north of highway 380, a tornado was reported by the sheriff in the small town of Keeter, southwest of Rhome. We were still too far away to see it. A couple of miles north of Ponder, lightning flashes allowed us to catch occasional glimpses of a low ragged wall cloud just above the horizon to our southwest. (This storm definitely had its roots in the boundary layer!) We drove through Ponder and stopped in the parking lot of a church to get a better look. It was a well developed wall cloud with a circular rain free base. NWS dopplar radar indicated a rotating updraft. At first, we could not see the wall cloud rotate because the lightning illumination was too infrequent, but the round base was a clue that it probably was rotating. Rotation was easily confirmed a few minutes later when an RFD clear slot developed and cut into the rain free base, wrapping around the SE side of the wall cloud. A second lowering developed on the nose of the RFD slot just west of Ponder. As the original lowering was occluded, a third lowering developed along the ESE side of the RFD slot. We left Ponder and drove east to escape 1/2 to 3/4 inch hail and to stay ahead of the wall cloud. The southern (third) lowering developed quickly into a large circular shaped updraft base with a nasty wall cloud near its center. It moved ENE across an area several miles south of Denton. The "second" lowering stayed intact and moved in a more northeastward direction toward Denton. We had witnessed an apparent storm split or the development of multiple flanks. I drove east from Ponder toward I-35W, while Bruce kept a watchful eye on the large wall cloud to our immediate southwest, which could be seen only with the aid of lightning. It was "charging hard" to the east, apparently being shoved by the RFD from the previous occlusion. Bruce observed several blue-green power flashes a few miles to our south underneath the wall cloud. Several miles and tense minutes farther east, we finally intersected I-35W and turned northeast toward Denton. Just inside the SW edge of Denton, we turned SE on I-35E. We were back on an intercept course with the largest and most intense mesocyclone so far. Just before we turned SE, the "second" partially rain wrapped lowering came into view again. It was just WSW of Denton. I felt it was the source of the 1/2 inch hail we drove into while on I-35E in Denton. Bruce had a rough time maintaining visual contact with the "third" wall cloud because of the blinding city lights of Denton, catching sight of it briefly during the brightest lightning flashes. Bruce observed several more power flashes under the wall cloud. This was an intense part of the chase because we were not certain how close the wall cloud was, nor were we sure of its exact movement. I was concerned that we might be converging with it as we drove SE from Denton and it continued moving ENE from its previously known position to our SW. Bruce did an excellent job as navigator, keeping us out of harm's way during a difficult night-time chase. When we got away from the city lights of Denton, Bruce got a good look at what he called a barber pole updraft. I quickly pulled over and jumped out to take a look. The meso was about three miles to our west, clearly illuminated by the lights of Denton, Lewisville and occasional lightning. It looked like a big barrel shaped layer cake to me. There was an obvious RFD slot being cut into the rain free base from the WSW. We both expected to see a tornado emerge from the darkness at any moment. Suddenly, outflow rushed across our position from the NW. The wall cloud had again been undercut by outflow. Time to move! We decided to drive a few more miles SE to highway 121, which would take us NE toward McKinney in pursuit of the meso. We were delayed a few minutes while driving through Tim Marshall's Lewisville, Texas. A few miles NE of Tim's home town, we drove under the western edge of the rain free base. We continued NE, carefully watching a new lowering develop a mile or two to our north. When we were near the Elm Fork of the Trinity River, where it crosses underneath highway 121, several bright green power flashes lit up the cloud base underneath the lowest part of the wall cloud to our NNE. The power flashes could have been due to a tornadic circulation, or it could have been due to a downburst, I can't say. We did not see a condensation funnel to the ground, although the wall cloud was quite low at the time. Within a minute or so after the last power flash, northerly winds in excess of 50 mph blew sand and small gravel into the open window of my van, sandblasting my face. Oouch! We paralleled the wall cloud until it dissipated after being torn apart by outflow. As the outflow intensified, a shelf cloud rushed overhead and continued several miles to our SE. The outflow slowed after only a few minutes allowing a new updraft base to form near its southeastern edge. This new cell apparently matured NE of Wylie and may have been responsible for the wind damage that occurred east of Farmersville on highway 380 in eastern Collin and western Hunt counties. (A mobile home was unroofed, several outbuildings destroyed, several trees uprooted, numerous large limbs broken and at least two barns blown apart.) We stopped on hwy 121 just west of hwy 289 to observe the new updraft base to the east where something interesting occurred. Even though the shelf cloud extended several miles to the east and south of our position, our winds suddenly switched from a rain-cooled northwestward breeze to a stiff 40 mph hot downburst from the southwest. The clouds overhead suddenly dissipated and stars were visible. In a few minutes, the wind changed to the south and then again to a moist ESE wind. Inflow? To what? Barely visible in the darkness, a small ragged, wind-torn updraft base and associated CB tower were moving toward us from the WNW. Maybe a shed decaying meso? I don't know, but the winds changed to the NW after it moved to our east. It seemed to be the cause of the weird wind shifts. Strange! I commented to Bruce that we might see a rope funnel appear from this thing at any time, as it took its last gasps. Several more green and occasionally white power flashes occurred to our east as the storm continued on its journey. We stopped on the east side of Allen, Texas, (Allen is located just north of Plano in Collin County on state highway 75), and shot a few lightning photographs as the storm slowly faded into the distant east. Pretty good night-time chase!