Jarrell Tornadic Thunderstorm Radar Loop

Jarrell TX Tornadic Thunderstorm

GIF89a Animation of Radar Reflectivity

From the SPC Cool Image Series

This reflectivity loop is centered on the WSR-88D unit at New Braunfels, between Austin and San Antonio, running from 1735 Z (12:35 pm CDT) through 0005 Z (7:05 pm CDT). The process of discrete propagation -- where in each step, a new thunderstorm develops separately from the larger, more intense predecessor then merges with it -- is evident throughout much of the loop. Discrete propagation caused the Jarrell thunderstorm complex to move southwestward along a pre-existing boundary (seen as a faint, beaded gray line extending southwestward from the storms through about 2200 Z). Part of the traditional concept of tornadic supercell evolution, "continuous propagation," is that new cell development occurs almost constantly on the immediate flank of the storm -- instead of in clearly separate steps as was the case here. This case, along with a handful of others discovered in the past few years, will force research meteorologists and forecasters alike to re-evaluate some ideas about thunderstorm processes leading to violent tornadoes.

The storms changed character significantly after about 2200 Z and became "outflow dominant" (outflow from the storms overwhelms the flow of air into them). The resulting outflow boundary is evident as the thin, curved band of gray surging southward out of the complex beginning at about 2230 Z. Storms in the complex were still severe during this stage -- and also after it merged with another complex moving southeastward from the Hill Country to the west -- producing numerous reports of wind damage and severe gusts up to 122 mph.

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