Low topped supercell produces tornado

On Wednesday at 16:45 CDT there was an EF-2 tornado in Bryan, Texas. The tornado was unusual in that it was produced by a low topped supercell. I found a monograph about this type of supercell here: Mini Supercell Thunderstorms

The radar screenshot below (from 16:40 CDT) shows the supercell that produced the tornado; the arrow points to it. It formed in advance of a fast moving MCS (squall line). It is clearly smaller and less intense than a typical supercell. Shortly after the tornado I was watching a meterologist on KBTX-TV who said the top of the cell as indicated by radar was no more than 20,000 feet. Also low topped supercells are known to form when instability is weak to moderate, which was the case Wednesday because CAPE was close to 1000 according to the SPC: Storm Prediction Center Mesoscale Discussion 435

The tornado happened without warning. There were no watches or warnings of any kind in effect for Bryan when the tornado occurred. But as stated in the monograph, low topped supercell attributes are more difficult to discern by radar at long ranges. The closest NWS radar was 70 miles away from the tornado.

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Reactions: Mike Z
Feb 20, 2018
Temple, Texas
Actually at the time of the tornado there was a Severe Thunderstorm Watch in effect for Brazos County. Truth be told, the storm went tornadic after it interacted with a boundary that had retreated northward from I-10. The complex that drew the tornado warning was part of a bookend vortex that formed near Cameron. Two separate entities and not tied to each other.
When the tornado occurred Severe Thunderstorm Watch 98 was in effect but it did not include Brazos County where Bryan is located. Severe Thunderstorm Watch 99, which did include Brazos County, was issued at 16:50 CDT, apparently in response to a report of the Bryan tornado by Texas A&M University meteorology students. According to the Public Information Statement, the tornado was on the ground from 16:42 to 16:47 CDT.

Michael G.

Apr 26, 2019
Aug 9, 2012
Galesburg, IL
If I remember correctly, most of the supercells associated with the December 1, 2018 outbreak in Illinois had tops between 20-30k foot (fairly low topped, especially some producing sig tors). Usually see that sort of thing up here along the surface low or cold core setups in late fall/early spring. You are correct though in that a lot of times its difficult to detect them due to the beam height of the radar and low topped nature of the storm. One reason why its imperative to have spotters in the field!