Background: On 10 April 1997 a mini-outbreak of tornadoes occurred in the central Texas Panhandle. Most of the severe weather came from a few isolated supercells that formed in the mid-afternoon. Additional severe storms developed during the late evening along a boundary left by the southern extent of the activity. The dominant storm of the day initiated on the dryline and was located at the south end of a broken line. This storm fit the description of an HP (heavy precipitation) Browning Model* supercell. Along a path from Seminole to Post, Texas, eight separate rotational "events" occurred from this system. Of special note, the storm deviated from the classic Browning Model after the first tornadic events. The storm developed numerous updraft regions that matured into a large (approx. 3+ mile diameter) circulation. The outer boundary of this type of circulation is generally the outward extent of the gust front. Within the major circulation, multiple (small) mesocyclones, consisting of large cumulus updrafts, produced numerous funnels and short track tornadoes. These rotating updrafts moved as eddies within the flow, and were located along the outer edge of the circulation. The tornadoes and funnels imbedded in this circulation were occasionally influenced by its rotation more than the storm movement. Two of the tornadic events on the north side of the major circulation, appeared to move west (cyclonically) as the storm proceeded east. All towns are in Texas, except for Hobbs, NM.
The Chase: The route for the intercept after leaving San Antonio was I-10 across South Texas, and north into the Texas Panhandle. This morning, deep moisture from the Gulf of Mexico was pouring up the Rio Grande. The high mesa country of South Texas was buried in fog, drizzle and intermittent rain. Sky conditions broke at Ozona giving way to fast moving cumulus against a warming blue sky. The turn north zigzagged through the pumping oil and gas fields of Pecos County. The sharp bite of the hydrogen sulfide gas made the value of this shortcut questionable. Upon entering Upton County, a row of towering cumulus lined the low western sky growing into tall towers in the distant northwest. The building clouds were in the target area for today's chase which was between Midland and Hobbs. Exactly where, would depend on the eastward progress of the dryline. The previous night's model runs played this scenario out in the microchips, favoring Plainview. Past knowledge of the region, and this type of pattern, led me to look further south. The main concern was the strength of the dry push coming off the Sacramento and Guadalupe Mountains. The MM5 forecast was for 15-20 mph surface winds and temperatures generally in the mid-seventies. The system appeared to be capable of higher downslope winds and surface temperatures. During the late afternoon a NOAA weather broadcast from San Angelo announced winds were blowing 45 MPH across the measuring station at Guadalupe Pass (8,000 FT MSL). Strong down- sloping winds off the mountains helped southeastern New Mexico heat into the low 80's and move the dryline east. At 1515 CDT tall cumulus began forming into a thunderstorm along the northwestern horizon. Eventually, two penetrating storm tops rose above the cirrus and severe warning was issued over NOAA weather radio. The white-knuckle driving began.
An hour later, while traveling north of Odessa, the severe warning expired. The south storm which had previously been feeding off a long line of cumulus towers (from the dryline) broke the connection. At this point the storm appeared to move off the dryline. The west flank of the storm died, promptly followed by the collapse of the storm top. Off to my east only tens of miles away lay a blanket of haze and low cumulus. While proceeding north of Andrews the low cumulus intersected the storm. A new cumulus tower started building on the south side of the storm. As a new flank developed, a wall cloud became visible to the north-northeast. Simultaneously, the top of the tower ballooned well beyond the old anvil cirrus. Chunks of clouds below the storm base began to tear loose pushing south. The remaining low hanging clouds located further east began to move rapidly to north. The rotation had started; so soon.
The first funnel spun up amazingly fast, less than fifteen minutes from the time the first updraft shot out of the south side of the storm. The funnel was not close, about five miles away, but plainly visible. Initially, two funnels condensed and rotated around each other and then combined as debris rose from the fields. A warning signal broke the squelch of the NOAA weather radio. It was a tornado warning for Gaines County. The funnel at cloud base narrowed and tightened as a second needle shot to the ground producing a classic elephant trunk tornado. About three minutes later the tornado bent erratically, thinned and appeared to lift off the ground. A lowering to the northeast of the dying tornado became more pronounced and began to spin. It was time to move east.
A concentric rotating tower had moved to just north of the road and the image of a funnel appeared out of the dust and haze. The second tornado grew larger while drawing an obscuring curtain of red dirt into the air. A thin sheet of striated rain wrapped around the circulation further reducing the visibility. Short strokes of lightning snapped to ground around the tornado adding to the violence of the scene. The base of the tornado swelled while rotating sheets of rain thinned the dust. About ten minutes after it crossed the road the tornado began to slowly narrow to a long tube. Baseball size hail briefly whacked the right side of the vehicle, then quit. Scattered large stones littered the roadside, but the width of the hail track was less than one mile. Rain and cool downdrafts engulfed the tube as it slowly disappeared from sight. The event with the two tornadoes began at 1725 CDT and lasted 20 minutes.
Strong south winds and blinding dust made traveling east on hwy 180 and north on Farm to Market Road (FM) 829 terrible. The storm, although still sporting a warning, had weakened. The main core of the cell stretched across the northeast horizon and a large optical vault was to the north. The vault appeared like the opening to a huge cavern. Rain and hail were occurring to the west and southwest. A low tail cloud formed marking the path of a high speed wind jet rising into a newly forming wall cloud. The easterly surface wind increased to an exceptional speed, lifting and condensing overhead. Tumbleweeds were not bouncing merrily along as usual, but were flying a couple feet off the ground. During this time a Lubbock News Channel 11 vehicle parked across the road. We chatted about the storm and decide to team-up. The strong inflow winds made it a challenge to get back to my vehicle.
The storm's back building ended and the eastward movement resumed. We moved northeast through Welch and east on FM 2053 past O'Donnell. While on FM 2053, a lowering began to rotate and we attempted to tape a few brief touchdowns. As we reached highway 87 storm chasers from Texas Tech began to show up and cars started parking along highway to watch the storm. Near the intersection of FM 3332 and 87 the storm began to release some pent-up energy. A large cyclonic circulation stretched about three miles in diameter from the north through northwest. The cloud material on the north side of this low hanging curtain of scud and fractus moved west, then turned south, and sped by us going east. A small mesocyclone to our northwest was first to spin-up. It put down numerous "filament funnels" that made a couple of turns around the main funnel and dissipated. These thin condensation funnels were making it to the ground, but no debris was visible. Their narrow snake appearance resembled suctions spots in a strong tornado. The large circulation was breaking down in may areas causing spin-ups along its circular path. Dry air descending into the circulation at random points wrapped around the rotating towers. Three distinct areas of rotation began to our east through north-northeast. The two south spin- ups formed funnels, and one extended condensation to the ground for a couple of minutes. This tornado was documented by a Texas Tech team. The largest circulation to the north-northeast had a curtain of rain rotating around the outside. A small but impressive mini-wedge tornado "appeared to be" on the ground in the rain. Late in the cycle of this circulation the rain diminished. We video taped the dissipating tornado moving west.
Gas was very low and a stop in Tahoka was necessary. It proved to be an error that would cost me a great photo opporturnity, but "walking" out of a tornadic thunderstorm is not fun either. The town was awash in flash flooded streets and hail. Blasting east on highway 380, the sun, now below the horizon, brightly illuminated huge cumulus towers pouring into the storm. Near the intersection of FM 1054 we came upon a tornado in progress (about three miles north). The funnel was black and contorted as it whipped across a field heaving intermittent surges of dirt in to the air. Individual smaller funnels spun around the base of the tornado. It was the third best tornado of the day, and firmly planted on the ground. The funnel's motion looked to be west along the northern edge of the main circulation. Unfortunately no pictures are available as we were moving in traffic at the time and obviously too late. Others may be able to confirm the true movement of the tornado. Vehicles equipped with brightly flashing lights lined the road accompanied by cars filled with wide-eyed kids and cameras hanging out the windows. The curtain of clouds, with the 360 degree rotation was breaking down due to shallow cold air under cutting it from the north. At the surface, this tornado had to be in the cold outflow air. At cloud base strong inflow was pouring into the tornado from the east. It dissipated in the cold air about one minute after we saw it.
The large circulation responsible for dominating the storm structure continued to deteriorate. Meanwhile, the intersection of the forward flank and precipitation core "took over" forming a ragged wall cloud. This circulation contained violent areas of rotation. "Angel hair" was drawing into the base of the mesocyclone. This occurs during high speed up-motion. Near the small community of Pleasant Valley a dirt (mud) circulation began on the ground. No obvious funnel was above this circulation; although, the news photographer stated he saw one before we stopped. Lights on the horizon were going out as this debris cloud passed. At this point we let the storm go. It was moving into an isolated area north of Post. Within the hour the storm would pass over White River Lake causing injury and death in the night.
* Reference: Browning Model. The widely accepted conceptual supercell model/drawing that shows one main flanking line, wall cloud and a precipitation core to the northeast. Additionally, it is used for spotter training to show the main elements of the supercell structure. The writer understands this example is dated and not all supercells fit this model, but many do. It is referenced to provide a familiar starting point to explain the visual appearance of the storm.
Closing: The events are stated as factually as the author perceived them and may be supported by
photography with the exception of one tornado east of Tahoka. This storm produced multiple funnels and
circulations that may, or may not have been tornadoes depending on one's definition. One may argue the
filament funnels were not tornadoes; although, visible condensation did reach the ground. Gene Moore
may be found at firstname.lastname@example.org
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