May 15, 2003 Texas and Oklahoma Panhandle Tornado Outbreak

An old-fashioned "cluster" tornado outbreak occurred over the southern high plains from the Texas Panhandle northward into extreme southwestern Kansas. Silver Lining Tours managed to see five tornadoes, including a classic ghostly white truncated/tapered cone tornado just west of Boise City.

Meteorology:

Today's convective outbreak was the handiwork of a compact, intense mobile upper-tropospheric trough (Fig. 1) that impinged upon the Texas Panhandle during the day. One aspect of this event that surprised many storm chasers/forecasters was the resiliency of the capping inversion and the amount of forcing it took to remove the CIN (convective inhibition - the "cap") farther southeast. Our team began the day in Amarillo and it wasn't long until we couldn't ignore the very moist, potentially unstable airstream pouring northwestward towards the area around Clayton, NM to Dalhart, TX to the western Oklahoma Panhandle. I was sitting at the home front providing forecasting and "nowcast" support. Fig. 2 shows a surface analysis from 18Z yesterday, and illustrates the things that I saw that made me very excited for the region centered on Dalhart, TX. This is a conventional surface plotting map showing the weather conditions at the regularly reporting synoptic stations; I've analyzed (using a 2-pass Barnes scheme with mid-range smoothing - Digital Atmosphere software) the surface equivalent potential temperature (THTAE; red solid contours) and wind vectors (gridded vectors). The key process revealed by this analysis is the THTAE "tongue" being advected into the threat region (see the wind vectors blowing northwestard within and around the pronounced tongue. Note that high values of THTAE have made it as far northwestward as Clayton, NM and Dalhart, TX. This is one way that the analyst can indirectly infer the degree to which the atmosphere is destabilizing due to moistening/heating of the low-level airmass and quite a bit of destabilization (with regards to upright moist convection) is occurring over the higher terrain of the NW TX panhandle, NE NM and W OK panhandle. One observation that particularly stood out (circled in red) is Dalhart, TX itself at 77/65 with a 1520 wind (wind blowing from the SSE at 20kt)! This represents a very unstable air "parcel" moving onto terrain that is nearly 4000 ft above mean sea level. This was more than enough meteorological evidence to get the SLT team into place! Note also the apparent "bubble" of relatively cool, stable air sitting over the eastern Oklahoma panhandle and northeastern Texas panhandle; this had me worried that even if storms. There was another consideration as well; the short-range numerical weather prediction models suggested that the capping inversion over much of the Texas panhandle would give way and storms would develop from northwest to southeast along the dryline but that this evolution would occur quite late, perhaps after 7:30pm. The idea was to "play" with chaseable storms early in the day in the aforementioned area and then drop southward later to intercept new storms developing along the dryline. This strategy resulted in the team intercepting two additional weak, short-lived tornadoes with a supercell storm in extreme southeastern Sherman County, Texas around 8:15 pm CDT.

Chase Summary:

To be given by Roger Hill, Tour Director.

Figures and Pictures:

Fig. 1: RUC analyzed 500 mb heights and wind; 0516/02z	Fig. 2: Conventional surface map with equivalent potential temperature (red solid contours) and gridded wind vectors, valid 18Z.	Boise City, OK tornado (and remaining clips following this one)
After the Boise City tornado dissipated, the group drives south and east in an attempt to intercept another supercell thunderstorm over southeastern Cimarron County, OK. Note the large blocky updraft and associated mesocyclone (view to the south).	Suspicious lowering is evident to their south near Griggs, OK.	Sitting at the office nowcasting and watching the evolution of storms on radar, I note a new storm moving into Dallam County about 15 miles WNW of Dalhart and I urge the group to break off the Griggs storm and target this one. Here is their first view of the large tornado being produced by this storm about 8 miles west of Stratford.	Another view of the tornado. Note in this picture the anticyclonic funnel beneath the flanking towers southwest of the main tornado! This was a full-fledged anticyclonic tornado moments before the group arrived.
They continue following the Stratford storm but it quickly evolves into an HP supercell near the Texas/Oklahoma border.	Note the horseshoe shaped updraft base, with precipitation-filled dry slot clefting the base. View to the northeast.	Another shot of the storm.	After following the previous storm all the way to Guymon, OK, I vector the group onto a new supercell cluster over extreme southern Sherman/northern Moore County, TX. This is one of the brief, weak tornadoes produced by that storm near Sunray, TX.
Another shot of the storm base and debris cloud beneath the dissipating funnel.	Here is a wider perspective of the storm a short time later. Note the classic supercell structure, including optical vault, lowered base and wrapping precipitation curtains.	Funnel cloud beneath the lowered base.	Wide view of the same storm; note the fat tapered funnel cloud.
		Two more shots to the left of the same supercell.