3

Tornado Warning Activities

WARNING ISSUANCE FROM VARIOUS SOURCES

The upper-air sounding from the NWS Midland office at 7:00 a.m. on Friday, May 22, 1987, showed the air mass over southwest Texas to be highly convectively unstable. The lifted index (LI) 1 on the morning Midland sounding was minus 6. The early morning West Texas Forecast Discussion issued by the National Weather Service Forecast Office at Lubbock at 3:41 a.m. noted the 24-hour LI prog 2 of more than minus 6 in its southern zones (see Appendix D ). The 9:15 a.m. West Texas Forecast Discussion 3 again brought attention to the possibility of thunderstorms in the Lubbock forecast area. The forecaster described the weather situation as looking “like a good aftn and eve for tstms . . . even . . . some severe.” The same message was carried in the afternoon forecast discussion sent at 3:08 p.m.

The Convective Outlook 4 issued by the National Severe Storms Forecast Center (NSSFC) (see Appendix D) at 1:43 a.m., and valid for the 24 hours beginning at 7:00 a.m., included a large section of west Texas in the area of slight risk of severe thunderstorms. Reeves County was just outside the slight-risk area. The Convective Outlook, updated at 2:12 p.m., shifted the slight-risk area westward to include Reeves County.

Severe thunderstorm watch no. 114, issued at 3:11 p.m. and valid from 3:45 p.m. until 10:00 p.m., encompassed a large portion of eastern New Mexico and parts of west Texas. The supplementary aerial outline derived from that watch, which specified the individual counties in the watch, included Reeves County.

The first radar indication of a severe storm in Reeves County was noted by Midland radar at 3:20 p.m. at 244 degrees, 108 nautical miles from Midland (or 20 miles northwest of Balmorhea) with a maximum top of



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NATURAL DISASTER STUDIES: SARAGOSA, TEXAS, TORNADO 3 Tornado Warning Activities WARNING ISSUANCE FROM VARIOUS SOURCES The upper-air sounding from the NWS Midland office at 7:00 a.m. on Friday, May 22, 1987, showed the air mass over southwest Texas to be highly convectively unstable. The lifted index (LI) 1 on the morning Midland sounding was minus 6. The early morning West Texas Forecast Discussion issued by the National Weather Service Forecast Office at Lubbock at 3:41 a.m. noted the 24-hour LI prog 2 of more than minus 6 in its southern zones (see Appendix D ). The 9:15 a.m. West Texas Forecast Discussion 3 again brought attention to the possibility of thunderstorms in the Lubbock forecast area. The forecaster described the weather situation as looking “like a good aftn and eve for tstms . . . even . . . some severe.” The same message was carried in the afternoon forecast discussion sent at 3:08 p.m. The Convective Outlook 4 issued by the National Severe Storms Forecast Center (NSSFC) (see Appendix D) at 1:43 a.m., and valid for the 24 hours beginning at 7:00 a.m., included a large section of west Texas in the area of slight risk of severe thunderstorms. Reeves County was just outside the slight-risk area. The Convective Outlook, updated at 2:12 p.m., shifted the slight-risk area westward to include Reeves County. Severe thunderstorm watch no. 114, issued at 3:11 p.m. and valid from 3:45 p.m. until 10:00 p.m., encompassed a large portion of eastern New Mexico and parts of west Texas. The supplementary aerial outline derived from that watch, which specified the individual counties in the watch, included Reeves County. The first radar indication of a severe storm in Reeves County was noted by Midland radar at 3:20 p.m. at 244 degrees, 108 nautical miles from Midland (or 20 miles northwest of Balmorhea) with a maximum top of

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NATURAL DISASTER STUDIES: SARAGOSA, TEXAS, TORNADO 50,000 feet and a video integrator processor (VIP)5 6 core. Hail was reported. The NWS office in Midland issued a severe thunderstorm warning at 3:24 p.m. for southwest Reeves County, valid until 4:30 p.m. (see Appendix D). At 3:30 p.m. a call was made to the Pecos Department of Public Safety (DPS) advising it of the warning and requesting reports of severe weather. At 3:45 p.m. a severe weather statement and radar summary were issued that headlined the severe thunderstorm warning for the county. A special weather statement at 4:10 p.m. included a report from the DPS of 1.75-inch hail in the southwest part of the county. By 4:35 p.m., radar indicated the thunderstorm top had fallen to 37,000 feet from its earlier top of 50,000 feet. A 4:50 p.m. severe weather statement and radar summary again highlighted the severe thunderstorm watch; detailed the location of five very heavy thunderstorms, including one near Toyah, which is 22 miles northwest of Saragosa; and repeated the report of golfball-size hail in the county. A second NSSFC Mesoscale Discussion6for Texas and New Mexico at 5:31 p.m. continued to focus on the area around Lubbock. It noted that very strong moisture convergence was located with a cell along the New Mexico and Texas border due west of Lubbock “with minus 10 surface lifted index feeding into it from the south.” The Reeves County storm maintained itself with little movement and by 6:05 p.m. was back to 44,000 feet. The 6:41 p.m. radar summary from the NWS office in Midland showed the storm to have a maximum top of 51,000 feet with a VIP 5 core. The 6:50 p.m. severe weather statement and radar summary mentioned very heavy thunderstorms at several locations, including south and west of the city of Pecos. The statement highlighted the watch and several warnings and mentioned that very heavy thunderstorms would continue to develop throughout the evening. By 7:20 p.m. the storm had become a supercell with the maximum top displaced directly over the sharpest reflectivity gradient on the inflow side of the storm. The storm had a VIP 6 core to 21,000 feet and a VIP 5 core to 31,000 feet. The NWS Midland staff initiated a call to the Pecos DPS office at 7:26 p.m. to request information on the thunderstorm between Saragosa and Toyah. At 7:37 p.m. the NWS issued a combined severe thunderstorm and flash-flood warning for southern Reeves County valid until 9:45 p.m. The warning located the storm 15 miles southwest of Pecos (or 15 miles northwest of Saragosa), moving slowly to the northeast. Amateur radio storm spotters reported a rotating wall cloud 4 miles west of Balmorhea on Interstate 10 at 7:46 p.m. and 2 miles west of Balmorhea at 7:48 p.m. These reports, together with radar clues, led to the issuance of a tornado warning for south-central Reeves County at 7:54 p.m. (see Appendix D ). The warning message located the thunderstorm 10 miles southwest of Pecos and included a call-to-action statement that described the storm as

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NATURAL DISASTER STUDIES: SARAGOSA, TEXAS, TORNADO dangerous and advised that proper tornado safety measures be taken. A call was made to the Reeves County Sheriff's Department in Pecos at 7:55 p.m. advising the department of the tornado warning. The county's Emergency Operating Center (EOC) at Pecos was activated by the emergency management coordinator around 8:00 p.m. after receipt of the tornado warning. The EOC is activated for tornado warnings but not normally for severe thunderstorm or flash flood warnings. The two tornado reports logged in the NWS Midland's severe weather logs came from storm spotters and from the Pecos DPS. The logs show some confusion in the communication of reports since one report was for the area 4 miles west of Balmorhea and the other was for the area 4 miles east of Balmorhea. The DPS report came from a public safety officer who was filling up his vehicle 's gas tank at a bulk gas plant at the 210-mile marker on Interstate 10. Following the initial warnings and reports of the tornado, the NWS issued a severe weather statement at 8:20 p.m. headlining the tornado warning for south-central Reeves County. The statement described the tornado report and noted movement to the east at 30 mph. Another severe weather statement issued at 8:30 p.m. again highlighted the tornado warning. It stated that a tornado was reported at a local school. A third severe weather statement at 8:40 p.m. continued to headline the tornado warning and again reported substantial damage in Saragosa. A new report of a funnel cloud 28 miles west of Fort Stockton from the Reeves County Sheriff's Department prompted an NWS tornado warning at 9:04 p.m. valid until 10:00 p.m., for southern Reeves and western Pecos counties. The warning noted that this was the same storm that had produced fatalities in Saragosa. The NWS Midland office issued several more warnings and statements throughout Friday night. (See Appendix E for a chronology of severe storm warning releases.) NOTES 1. The LI refers to a relative measure of instability in the atmosphere expressed as a numerical value. It is arrived at by lifting a parcel of air dry adiabatically to its point of saturation and then along the moist adiabat to some reference pressure level such as 500 or 300 millibars. At that reference level, the temperature of the lifted parcel is compared to the ambient air temperature to arrive at an index value. The adiabatic process refers to the thermodynamic change of state of a system in which there is no transfer of heat or mass across the boundaries of the system. A specific lapse rate (i.e., the rate of decrease of temperature with height for a specific air parcel) is associated with the assumption of a dry or saturated condition of the air parcel. 2. “Prog” refers to a 24-hour forecast chart of projected lifted indexes. 3. The West Texas Forecast Discussion is a message prepared four times daily

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NATURAL DISASTER STUDIES: SARAGOSA, TEXAS, TORNADO by the Lubbock Weather Service Forecast Office (WSFO) to describe current meteorological reasoning concerning present and anticipated weather. These discussions relate present synoptic-scale weather situations to numerical guidance outlining the forecasters' reasoning for the content of the upcoming forecast package. All WSFOs prepare these discussions, which are a vehicle for forecast coordination. 4. A Convective Outlook is a message routinely prepared by the NSSFC outlining areas where thunderstorms are expected, including areas where thunderstorms may reach severe limits. It encompasses the entire 48 contiguous states and is used as guidance by WSFOs. 5. VIP is the digital video integrator and processor equipment used on NWS radars. It was developed to meet requirements for continuous quantitative data output. The radar video signals resulting from precipitation echoes are integrated in 1-nautical-mile segments over a range of 115 nautical miles and displayed on the radar planned position indicator (PPI) in a step function intensity modulated sequence. The VIP (or, more accurately, DVIP) processes the output of the radar 's logarithmic receiver to produce up to six levels of intensity data corresponding to preselected categories of estimated rainfall rates. This permits the constant monitoring of echo intensities, within the six categories, with each rotation of the radar antenna. 6. A Mesoscale Discussion is an unscheduled discussion prepared by the NSSFC describing meteorological factors related to existing mesoscale features. It focuses on a small area that moves as weather systems move.