How Tuesday’s tornadoes formed and why more could develop this week

Weather Blog

Video above from @TornadoTrackers/Gabe Cox as he monitored the development of a tornado near Smithville.

Tornadoes touched down in at least two Central Texas locations Tuesday, possibly a couple more. Radar and viewer reports indicate several tornadoes may have formed in severe thunderstorms over Caldwell, Bastrop and Lee counties.

The National Weather Service is examining the damage, photos and other data to determine where tornadoes struck and how intense they were. A survey team reported Wednesday the Caldwell County tornado was an EF-0 with 85 mph winds when it struck McMahan. The Smithville area tornado was also rated EF-0 with 80 mph winds. Damage to a barn and trees was reported near McMahan, but several residences were damaged along FM 2571 near Smithville.

So why did multiple tornadoes form on a day when the severe storm outlook called for a low risk of tornadoes? It all started the night before as a large complex of storms developed from the Texas Panhandle to Mexico. Overnight, several small low-pressure centers emerged, known as MCVs, or mesoscale convective vortices. These areas of rotation are usually only 30-60 miles wide, but can help trigger supercell thunderstorms when combined with enough moisture and some veering of the wind direction from ground level through several thousand feet above the surface.

Rotating wall cloud above tornado near Smithville airport – Photo: Robert Tamble

The vortex that slowly approached the Hill Country Tuesday morning not only helped generate rotating thunderstorms but also several wall clouds, funnel clouds and tornadoes in the storms that formed south and east of the Austin metro counties.

Funnel cloud, possible tornado near Smithville – Photo: Gabe Cox – @TornadoTrackers

While hard to predict, MCVs are notorious for helping produce small, short-lived tornadoes, especially in a tropical atmosphere. The slow movement of Tuesday’s disturbance also resulted in several rounds of storms, producing 4-5″ of rainfall and some flash flooding.

Tornado near Smithville – Photo: Gabe Cox – @TornadoTrackers

A low-pressure system of a different type may yield more severe weather and heavy rainfall this weekend. While it’s too soon to be certain there will be severe thunderstorms or tornadoes, troughs of low pressure in May similar to the one we are expecting to move into Texas this weekend have been known to produce tornadic thunderstorms and flash flood-producing rainfall in the past. The good news is the setup does not look favorable for a widespread severe storm outbreak, but a more scattered threat.

The evolution of the weekend storm is uncertain, but the National Weather Service is predicting the possibility of 3-5 inches of rainfall over the next 7 days, with much of that rainfall occurring from late Friday through Saturday. On already saturated soil, flash flooding would be likely if that much rain falls.

Stay with the First Warning Weather team and download the free KXAN Weather App to be prepared for our next round of storms.

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