Surface Analysis Near and Within the Tipton, Kansas, Tornado on 29 May 2008
Total Page：16
File Type：pdf, Size：1020Kb
370 MONTHLY WEATHER REVIEW VOLUME 139 Surface Analysis near and within the Tipton, Kansas, Tornado on 29 May 2008 BRUCE D. LEE AND CATHERINE A. FINLEY WindLogics, Inc., Grand Rapids, Minnesota TIMOTHY M. SAMARAS National Technical Systems, Littleton, Colorado (Manuscript received 13 April 2010, in final form 7 September 2010) ABSTRACT Data collected by a mesonet within the near-tornado environment and in the Tipton tornado on 29 May 2008 provided a rare opportunity to analyze rear-flank downdraft (RFD) outflow properties closely bounding a tornado and to characterize parcel thermodynamics being ingested into a tornado from the rear-flank downdraft. Parcels moving into the tornado on its right flank had very small negative buoyancy and con- siderable potential buoyancy. Measurements within and very near the tornado showed similar buoyancy characteristics to the storm inflow. Analyzed surface divergence and videographic evidence indicated that the RFD outflow just to the right and wrapping in front of the tornado was supported by parcels moving out of a narrow downdraft bordering the right flank of the tornado. Surface flow field analysis showed that parcels moved out of the downdraft-associated divergence region and into the right side of, as well as in front of, the tornado. An internal RFD surge boundary was positioned roughly 0.5 km in front of the eastern edge of the analyzed divergence region and implied downdraft. The broader RFD outflow thermodynamic characteristics were consistent with recent research with only small negative buoyancy and substantial potential buoyancy; however, convective inhibition was considerably higher than typically found in other tornadic cases. This latter characteristic was emblematic of the broader storm environment on this day. Parcels making up the RFD outflow originated from low-levels, consistent with recent findings for tornadic rear-flank downdrafts and in contrast to past historical indications for the rear-flank downdraft source region. 1. Introduction datasets within this region exist. Observational studies have shown that rear-flank downdraft (RFD) outflow The ability to understand the processes involved in surrounds or nearly surrounds the tornado (e.g., Brandes tornadogenesis, maintenance, and decay is dependent, in 1977, 1978; Lemon and Doswell 1979; Markowski et al. large part, on obtaining observations in key regions of 2002, hereafter MSR2002; Wurman et al. 2007b); thus, the supercell thunderstorms that historically have been very properties of the near-tornado RFD outflow are espe- difficult to gather. One such area is within roughly 1 km of cially important across the tornado life cycle. In particu- the tornado or tornadogenesis region that contains the air lar, buoyancy characteristics of the RFD outflow may play parcels that ultimately comprise the tornado inflow. With an important role in the development, intensification, the rapid evolution of mobile Doppler radar (Wurman maintenance, and diminution of near-surface rotation et al. 1997; Bluestein and Pazmany 2000; Bluestein and (e.g., Leslie and Smith 1978; Davies-Jones and Brooks Wakimoto 2003), a considerable number of kinematic 1993; Adlerman et al. 1999; Davies-Jones et al. 2001; datasets have been gathered in tornadogenesis or tornado Markowski 2002b; Markowski et al. 2003a, 2008). proximate regions; however, very few thermodynamic The association between supercell thunderstorm RFDs and tornadoes has long been recognized (Markowski 2002b). More recent research has focused on direct mea- Corresponding author address: Dr. Bruce D. Lee, WindLogics, Inc., Itasca Technology Exchange, 201 NW 4th St., Grand Rapids, surements within the RFD outflow by utilizing a mobile MN 55744. mesonet (Straka et al. 1996). The analysis of MSR2002 E-mail: [email protected] and Grzych et al. (2007, hereafter GLF2007) revealed DOI: 10.1175/2010MWR3454.1 Ó 2011 American Meteorological Society Unauthenticated | Downloaded 10/06/21 05:18 PM UTC FEBRUARY 2011 L E E E T A L . 371 compelling evidence supporting the general conclusion tornado from this storm formed near Glen Elder Dam that tornadic and nontornadic supercells had differing and eventually produced EF-3 damage southwest of RFD thermodynamic characteristics. Specifically, the Jewell, Kansas (NCDC 2008). results of MSR2002 (which are supported by GLF2007) TWISTEX was conducted during May and June of show that tornado likelihood, intensity, and longevity 2008 with a domain that included regions from the upper increase as the near-surface buoyancy, potential buoy- Midwest through the southern Great Plains. The project ancy, and equivalent potential temperature ue increase had a typical complement of three mobile mesonet ve- in the RFD outflow, and as the convective inhibition hicles and a probe vehicle that transported an array of (CIN) in the RFD outflow decreases. HITPR probes and two video probes [see Karstens et al. Although a substantial number of mobile mesonet (2010), their Fig. 3]. The primary objective of the field RFD outflow datasets have been collected and analyzed portion of TWISTEX was to gather thermodynamic and over the past approximately 16 years to determine the kinematic data with a mobile mesonet in the RFD out- association between RFD outflow thermodynamic and flow region near tornadoes and the adjacent RFD gust kinematic character and the tornadic nature of a supercell front (RFDGF) region while concurrently gathering (Markowski 2002a; MSR2002; Lee et al. 2004; Finley and thermodynamic data with the HITPRs in or very near Lee 2004; GLF2007; Hirth et al. 2008), there exist com- tornadoes. The sampling goal was designed such that a paratively few RFD outflow mesonet datasets with sam- combined thermodynamic and kinematic mapping could pling within very close range of a tornado. Additionally, be done in the tornadogenesis and tornado maintenance with the exception of the Verification of the Origins regions while also addressing project objectives involving of Rotation in Tornadoes Experiment (VORTEX; near-surface tornadic flow field analysis with the aid of Rasmussen et al. 1994) deployment on 8 June 1995 near the video probes. Allison, Texas (Winn et al. 1999; MSR2002, see their Fig. 10), no published cases existed before the present 2. Synoptic and mesoscale environment dataset was obtained in which coordinated sampling of the near-tornado RFD outflow by a mobile mesonet was Conditions over northern Kansas and southern undertaken while in situ probes were collecting near and Nebraska on the evening of 29 May were generally very internal tornado observations. favorable for tornadic supercells. The outbreak was as- During the Tactical Weather-Instrumented Sampling sociated with a southwest flow upper-level pattern in In/Near Tornadoes Experiment (TWISTEX), a mobile place over the southwestern and central United States as mesonet and an in situ thermodynamic probe called the shown in the 0100 UTC Rapid Update Cycle (RUC) Hardened In Situ Tornado Pressure Recorder (HITPR; model (Benjamin et al. 2004) 500-mb analysis in Fig. 1. Samaras and Lee 2004) collected data near and within the During the day on 29 May a short wave moved into the tornado that occurred in the vicinity of Tipton, Kansas, central plains, and by evening the right entrance region of on 29 May 2008. Additionally, a seven-camera in situ the jet streak associated with this short wave was located video probe was deployed approximately 10-20 m south over northwest Kansas and southwest Nebraska as shown of the thermodynamic probe to record full 3608 videogra- in Fig. 1. This jet streak was apparent up to the 350-mb phy of the tornado passage. The tornado sampled (here- level. An upstream short wave may be seen over Arizona after called the Tipton tornado) was just one of many and western New Mexico but it is not believed to have tornadoes produced by its parent supercell (NCDC 2008). played a role in influencing the deep-convective environ- The Tipton tornado occurred in open country and re- ment for this case. In conjunction with the central Plains ceived an EF-1 rating with damage relegated to power short wave passage, a strong low-level jet was in place poles and trees during its estimated life of 23 min [based across much of southern and eastern Nebraska and most on TWISTEX tornadogenesis observation and NCDC of Kansas, as seen in the 850-mb vector winds in Fig. 1. A (2008) reported time of dissipation]. With the tornado substantial area within this region extending from west- passing over the in situ probes, with one mesonet station central Kansas to south-central Nebraska had 850-mb positioned 235 m south of the HITPR (roughly 190 m southerly winds exceeding 25 m s21. When coupled with south of the tornado edge) and another mesonet station the surface flow to be presented next, the deep-layer located up to 1 km farther south, the dataset collected vertical wind shear environment over much of Kansas and provides an opportunity to determine the thermody- eastern Nebraska was quite favorable for supercell thun- namic character of the flow getting ingested into the derstorms. tornado from the RFD outflow along the right flank At the surface, an area of low pressure was situated (looking downstream) of the tornado. It is worth noting under the right entrance region of the upper-level jet that just before the Tipton tornado dissipated, the next streak in northwest Kansas (Fig. 2). Strong southerly to Unauthenticated | Downloaded 10/06/21 05:18 PM UTC 372 MONTHLY WEATHER REVIEW VOLUME 139 FIG. 1. Geopotential height field at 500 mb (m, solid lines) and FIG. 2. Surface synoptic analysis at 0100 UTC 30 May 2008 with vector winds at 500 (black arrows) and 850 mb (gray arrows) for mean sea level pressure and subjective frontal positions. Temper- 0100 UTC 30 May 2008 (from RUC analysis). The maximum wind ature (8F), dewpoint (8F), and wind (half barb 5 kt; full barb 10 kt) vectors (m s21) are shown in the lower right.