The author witnessed a very strange phenomena during the early evening of May 14th , 0100Z to 0300Z, with respect to observing a stationary SuperCell, no directional movement for over 2 hours, centered in west central Dawson County. The long time duration storm became supercellular after several discrete convecting storms converged becoming an amalgamated composite which NEXRAD radar revealed, through progressive time loops, to spin counter-clockwise for over 90 minutes.
Mesoscale synoptics were favorable for thunderstorm development due to moderately steep mid and lower lapse rates and abundant low and mid level moisture advecting from the south and southeast providing for high lifted indices producing MLCAPE above 2500 J/kg east of a pronounced dry line which was moving beyond the Central Permian Basin by mid afternoon due to strong surface heating in far western Texas. Directional shear was favorable due to the previously mentioned southeast surface and low level WAA coupled with western flow aloft at mid and upper levels of the troposphere. However the speed shear was not impressive as only 25-30 knots were noted at the 500-300 mb levels from the 0000Z sounding at MAF. The SPC listed the Permian Basin in a Slight Risk category but initiation of convection was a concern in order to overcome a weak Cap due to a lack of upper level forcing. Low level convergence would have to provide the needed lift, noting that in the afternoon a cyclonic surface low had developed, centered near MAF, which might aid in convective initiation.
It was noted around 00Z from NEXRAD radar that a boundary was evident and moving northwest, north of Midland, in an arcuate fashion (may have been increasing moisture return, retreating demarcation of the dryline; MAF sounding at 00Z revealed surface dewpoints lowered to 46 with respect to higher values, above 60, further east). Convection initiated along this apparent observed boundary in southwestern, central and east central Dawson County. The author left Midland, traveling north on SH 349, once it became apparent that storm towers were growing. While driving and monitoring MAF radar via Mobile Threat Net, it became apparent that the convection was congealing into a central updraft foci. The first image was captured from central Martin County looking north into southwestern Dawson County at back building convection towers along a developing rear flanking line of a centralized updraft central core, noted beneath and to the west (right of image).
The next image, below, after crossing the intersection of SH 176 and proceeding north, revealing lowering of the updraft rain free base, followed by another closer image capturing a small tail inflow extending from a developing Wall Cloud .
Screen capture of the radar presentation, as the
author neared the Martin/Dawson County line, illustrating the developing SuperCell with noted V-notching signature, indicative of venting (diffluence) aloft. Another image is captured after driving nearer to the circulation alongRR 829 north of Patricia close to 0145Z. The next image, from same location as previous, illustrates strong inflow surface wind directed toward updraft base as noted by sand blowing across road.
At this time the author continued to drive north along RR 829 until reaching the intersection of FM 2052 near a church in southwestern Dawson County and pulled off the road for the remainder of the duration of filmed documentation. It was near 0200Z and had become to dark to photograph with the digital camera so the next series of images are from video stills which were enhanced to help discern silhouette(s). It became apparent that the lowered updraft base had taken the appearance of a oval disc and that a pronounced Wall Cloud was descending. The images were aided in lighting from the RFD clear slot which helped illuminate the observed features beneath the updraft base. The first video still demonstrates the oval disc shaped updraf
t
base. The next several video stills reveal a descending Wall Cloud and attached funnel.
The next image and possibly the proceeding define a funnel which may have reached the ground as tornado due to the dust swirl beneath.
The above images were generally taken after 0200Z and before 0230Z. In all this was a very strange event with respect to a developed SuperCell in an environment of high lifted indices but with very weak speed shear. The long duration over a central position without any appreciable movement was also unique and undoubtedly produced torrential rain and large hail over a confined limited area. The canopy spread from this lone Supercell, eventually collapsing around 0330Z, covered six counties along a west to east transect from the updraft.
