Seven Occlusions Road

Today’s title is, of course, a shameless meteorological modification of that of the old easy listening ditty by The Eagles.

Texas state road 146 rolls along the Panhandle plains from about 4 miles north of Tulia through Vigo Park, halting just short of the Caprock Enscarpment where it meets state road 207. This highway is surrounded by almost treeless, tabletop flat countryside, with numerous safe pull-offs and an abundance of north-south options along intersecting section roads. Straight as can be, avoiding major towns, with almost no hidden hazards or mandatory stops, it is, in many respects, the ideal storm chase road. The only problem with it is strategic: the unease that comes from knowing that any supercell cruising eastward just north of that road will cut off the observer at the only option leading off the caprock (highway 207), several miles farther north and in the path of the threat.

That’s what happened to us on 11 June, but not before we witnessed seven (yes, 7) mesocyclone occlusions and approximately three tornadoes with a storm that started off in doubt. The initially high based supercell struggled to survive its journey through some hot, deeply mixed inflow air; but the large area of its rain free base gave us cause for hope. We had latched onto this storm from its very beginning, blowing off an earlier developing and initially more promising supercell near Amarillo partly because of intervening storms that would hinder our approach.

The future Vigo Park storm underwent an amazingly fast transition from amusing lollygagger to menacing potential tornado producer: less than five minutes! We had been watching the storm from north of Tulia, hoping it could survive long enough to reach an old outflow boundary and do something interesting. While repositioning by a few miles, a much lower and closer wall cloud formed under a surprising new mesocyclone whose existence I had no evidence of just a few minutes before. This second wall cloud and mesocyclone formed almost overhead and just to the NW with astonishing suddenness, then moved off slowly to the north, spinning rapidly but not following through on its threat to yield a tornado.

We would witness five more mesocyclone occlusions (birth to death) — seven total — along a mere 20 mile stretch of that road. Each time one circulation would curl itself northward and wrap up, another formed just to its ENE, and the entire storm would stall for about 10-15 minutes.

A couple of brief tornadoes of no consequence happened during that interval; but the most fascinating thing was this supercell’s tendency to spawn and extinguish mesocyclones, one after another, over fairly small intervals of distance and time, and to go stationary each time before lurching east again. A cascade of tornado warnings poured forth on this storm, and justifiably so.

The sixth occlusion finally produced a noteworthy tornado (actual and enhanced digital imagery) that lasted several minutes, as if the storm had decided to wait patiently and politely for the rolling hordes of electronically endowed “yellow-donut chasers” who initially had targeted the Amarillo supercell.

The storm then cut off all but the most daring or risk-taking, its seventh mesocyclone swirling directly across the 207 road that plunged northeastward into the Palo Duro Canyon. We started to take that route, but thought better of the move after rocks began tumbling from the canyon walls onto the roadway. It was time to back off, convene with other observers, and appreciate what we had just seen, at least as much for its fascinating storm-scale processes as for its appearance or tornado production.



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