Mission Summary 6/02


On 2 June, VORTEX obtained much-needed data on two storms which produced violent tornadoes. The storms formed in a region of strongly backed low-level flow with modest westerly flow aloft, yielding strong deep shear. CAPE was larger then 3500 J/kg. The target area for VORTEX for storm initation was Clovis, New Mexico. Storms formed in this area in the late afternoon.
The first storms seemed somewhat disorganized. However, inflow quickly increased to 40-50 kt, so we felt that the storms had a lot of potential for becoming supercells.
The first target storm moved NE along US 60 toward Friona, TX. When the storm was near Bovina, inflow became so strong that visibility went to zero in blowing dust, and power lines were torn down at a distance of 15 km SE of the storm. Some surface teams were forced to turn away from the storm because of these conditions. The other teams which were closer to the developing mesocyclone reported winds of 30-50 kt flowing toward the mesocyclone from all directions. The mobile Doppler scanned the storm from a distance of 12 km and observed very strong low-level horizontal shear and reported this information in realtime to the Field Coordinator.
The first violent tornado formed just SW of Friona, moved across the southern fringes of the community, and then across the east side of town. It traveled for several miles further NE to the area north of Black, TX. At Friona, a large grain elevator was destroyed. The airport was completely destroyed, with the most significant damage being to a large steel building. The anchor bolts holding the columns of this building were ripped out of the concrete slab, with part of the slab going with the bolts. The heavy beams were left in a twisted heap. One I-beam became a missile and was thrown about 100 meters.
The cemetery just north of the airport was also heavily damaged. There, trees had most of their branches removed. A several-ton railroad boxcar which served as a storage building bounced through the cemetery, destroying monuments and gouging a 2-foot deep hole through an asphalt drive and into hard-packed soil. The boxcar traveled about 100 meters.
At this time, VORTEX is reluctant to establish an F-scale rating because of the usual problems with this rating system. In much of the VORTEX region, the probabilities are miniscule of tornadoes striking areas with residential/business structures from which damage ratings can be obtained. I can say that the visual impression of the damage northeast of Friona is consistent with other damage swaths I have seen that were rated high-end F4. Officially, I would have to say that this tornado was a significant, violent tornado, and assign it the rating of F-unknown. Of course, I don't speak for all of the VORTEX investigators in this informal information statement.
After the Friona tornado became rain-wrapped, attention shifted to a new mesocyclone just SE of Friona. This mesocyclone was due to move into a region with very few roads, and yet another mesocyclone was developing SW of Dimmitt, so VORTEX targeted that storm (at times, more than a half-dozen mesocyclones were in existence over a few-county area, making the intercept very risky in terms of choosing the "best" storm and staying safe).
As the mesocyclone approached Dimmitt, teams quickly converged on their correct storm-relative positions around Dimmitt (kudos to all participants!). The mobile Doppler scanned the near-ground mesocyclone region south of Dimmitt briefly. A tornado developed quickly on the south side of Dimmitt, moving cyclonically about the mesocyclone to just east of Dimmitt, and then curved back northwestward. Mobile mesonet data were obtained in all quadrants of this tornado within 3 km. Video was obtained from several sides.
The mobile Doppler obtained tremendous data as the tornado moved in an arc around the Doppler position on the 3 km (!) range ring. The tornado debris cloud itself appears in the reflectivity data. It is largest in the boudary layer, with high reflectivities all the way to the axis. The debris cloud narrowed above the boundary layer, and the core had very low reflectivity. Higher up, the tornado widened. The tornado reflectivity contained a number of fascinating asymmetries, including a high-reflectivity "inflow band" in the boundary layer. Doppler velocities are strong (folded two or three times with a 16 m/s Nyquist velocity), and the flow is smooth enough that the velocity data can be unfolded easily.
This tornado was also a violent tornado, with the same F-scale assignment problems as discussed above. Where structures were damaged, the damage (tentatively) was rated F3. However, when the tornado crossed TX 86, it removed the pavement in a 10 m wide swath over a length of 100 m (don't quote me on those dimensions... a real damage survey report will be forthcoming). The asphalt was thrown over 200 m into the adjacent field. Power poles were snapped at the ground. Vehicles were totally destroyed, with reports of two truck trailers missing entirely. Once again, my personal opinion is that the "honest" F-scale rating, as with most Plains tornadoes, is "F-unknown".
As the Dimmitt tornado was in progress, another, less significant tornado was occurring about 10 miles north of Dimmitt associated with the mesocyclone (noted above) which formed southeast of Friona.
The research aircraft were forced to fly on the west sides of these storms because of the widespread intense convection. A large number of pseudo-dual Doppler volume scans were collected by the aircraft at somewhat greater ranges than normal.
In summary, VORTEX has obtained a rich data set on one significant tornado event (Dimmitt tornado). Data were obtained which will allow us to document the entire life cycle from genesis through the rope-tornado demise. We obtained a good data set at Friona, although that event was sampled somewhat less well than the Dimmitt tornado. We believe these data sets will compliment the many rich data sets we have for non-tornadic supercells, as well as those representing tornadic storms with weaker tornadoes.
To those of you who intercepted either storm who aren't associated with VORTEX: VORTEX is very interested in obtaining copies of any video footage or other photographic material you may have. Contact me via email at rasmussen@nssl.noaa.gov, or by phone at 405-366-0560.

Erik Rasmussen
Jerry Straka

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