1 P10.15 TWO TORNADIC THUNDERSTORMS IN OSTENSIBLY WEAK DEEP LAYER SHEAR ENVIRONMENTS IN SOUTHEASTERN COLORADO: CYCLIC SUPERCELLS OF 25 MAY (KIOWA COUNTY) AND 31 MAY (BACA COUNTY) 2010 John Monteverdi*, San Francisco State University, San Francisco, CA Michael Umscheid, National Weather Service, Dodge City, KS Evan Bookbinder, National Weather Service, Kansas City/Pleasant Hill, MO 1. INTRODUCTION On 25 May and 31 May 2010, long-lived, cyclic tornadic supercells (Bunkers et al. 2006) occurred in Kiowa and Baca Counties, respectively, in southeastern Colorado. While the occurrence of tornadic supercells in this portion of the country is not unusual climatologically, what ultimately led to our interest in documenting these events was that neither storm developed in a shear environment that conventional wisdom suggested could support long- lived cyclic supercells.. Rotating storms were anticipated on both days, however the weak deep layer shear environments (exemplified by winds initially 10 m s-1 or less at 500 mb) suggested that the rotating phase of such storms would be brief because precipitation would overwhelm the updraft areas before storms could take advantage of the low-level shear environment. In addition, in both cases, initial hodographs showed that ground-relative winds at the top of the 0-3 km layer were very light, despite enormous clockwise loops in the hodographs. Thus, interrogation of ground relative winds in this layer might lead some forecasters to the conclusion that storms might have insubstantial inflow. The Kiowa County storms of 25 May produced at least three supercell tornadoes (Fig. 1) as it moved into western Kansas northwest of Tribune (see Table 1). The Baca County storm of 31 May produced two supercell tornadoes near Pritchett and eventually moved on to the southeast producing an additional significant, long-lived, and long track tornado (Fig. 2) along with other shorter-lived tornadoes as the storm moved into the Oklahoma Panhandle (see Table 1). The authors noted separately some other unusual aspects of the storm development on these two days. The primary author, Monteverdi, documented the Kiowa County storms and noted that initial storm motions deviated almost 100 degrees from the anticipated storm motions computed using classical hodograph analysis techniques (i.e., Bunkers technique). *Corresponding author address: Prof. John P. Monteverdi, Dept of Geosciences, San Francisco State University, 1600 Holloway Avenue, San Francisco, 94132; e-mail: [email protected] Figure 1 – Tornado associated with the Kiowa County storm near Towner, CO at around 2155 UTC May 25. Photo by John Monteverdi. Figure 2 – Tornado associated with the Baca County storm of May 31 near Campo, CO at around 0025 UTC June 1. Photo by Mike Umscheid.2 Figure 3 – Locations of tornadoes reported in Storm Data (red triangles) and of other possible tornadoes/funnel clouds (orange triangles) not reported in Storm Data. with UTC time stamps on 25 and 26 May 2010. Circles indicate updraft location as determined from analyses of the KGLD radar data, discussed in section 2. Figure 4 – As in Fig. 3, except for May 31 and June 1, 2010, and KPUX as source of radar data. Yellow triangles show locations of funnel clouds.3 Umscheid documented the entire life cycle of the Baca County storms and also noted that storm motions were nearly 90 degrees from the anticipated storm motions for a portion of its life. It was these observations that led us (a) to consider the hypothesis that the unusual storm motions created storm-relative wind and shear profiles favorable for long-lived tornadic supercells; and (b) to realize that these cases were united not only by similar kinematic environments, but also by the probable fact that the unusual storm motions transformed the risk from minimal to significant that tornadic storms would occur, despite conventional wisdom. Initially, the authors were separately considering researching the storm they observed, but eventually realized that both events shared some very unusual, but common, characteristics. Besides the kinematic aspects of the storm initiation environments, we both separately noted the importance of updraft interaction with several boundaries in both areas as a source for low level rotation and storm propagation. So, we decided to combine our studies into one, stressing the common aspects (but noting the differences). The authors view this conference presentation as a pilot study. In this manuscript and poster, we seek merely to examine the evidence that our hypothesis has basis, and that there is enough justification to seek a formal publication in the future. Hence, the purpose of this study is to provide a summary of the synoptic and mesoscale environment within which these storms formed. In particular, we seek to examine the thermodynamic and wind shear and aspects of the subsynoptic environment that helped foster initially unusual storm motions that transformed this event to one supportive of briefly rotating, nearly pulse thunderstorms to one that should have been anticipated (in hindsight) to support tornadic supercells. Sheridan Lake/Towner/Tribune Tornado Times: 25 and 26 May 2010 UTC Location County State Lat Lon 2141 3 SW TOWNER KIOWA CO 3844 10212 2153 SHERIDAN LAKE KIOWA CO 3847 10229 2155 TOWNER KIOWA CO 3847 10208 2158 3 SSW SHERIDAN LAKE KIOWA CO 3842 10231 2320 4 N TOWNER KIOWA CO 3853 10208 2349 9 N TRIBUNE GREELEY KS 3860 10178 Pritchett/Campo Tornado Times: 31 May and 1 June 2010 2053 11 SW PRITCHETT BACA CO 3726 10300 2103 6 SSW PRITCHETT BACA CO 3729 10290 0009 3 S CAMPO BACA CO 3706 10258 0059 11 NW KEYES CIM OK 3692 10239 0151 4 WNW EVA TEXAS OK 3682 10197 Table 1 : Tornado times and locations reported to SPC and logged in Storm Data. 2. STORM EVOLUTION AND HISTORY A complete analysis of Level–II Weather Surveillance Radar 88 Doppler (WSR-88D Goodland, KS [KGLD] for 25 May; Pueblo, CO [KPUX] for 31 May; Amarillo, TX [KAMA] near the latter stages of 31 May) was conducted for both cases starting from storm initiation and ending