Austin’s Invisible Rain Dome Is All a ‘Balcony Fault’

One of the benefits of spending more than 30 years forecasting in Texas is learning about local weather patterns in the forecast area. As a meteorologist who has seen hundreds of storm events unfold across the region over time, you begin to recognize the patterns that storms often follow, even if there is no obvious reason for this outcome.

And in Central Texas, even amateur weather watchers have noticed one pattern in particular: Austin’s invisible rain dome.

The scenario is as follows: Severe thunderstorms approach Travis County — with the city of Austin in the center — from the west, bringing heavy rain and resulting in severe weather. But as the convective line moves across the county, the storms suddenly weaken, sometimes almost dissipating.

Then, as the line moves into eastern Travis County, storms quickly intensify and flare up again as they head east. The result is heavy rain both west and east of the city, but little or no rain in the central part of Austin.

This radar view from April 5 is an excellent example.

Powerful storms suddenly lost intensity as they emerged from the hills west of Austin, shooting back across the eastern edge of the city.

Austin’s invisible rain dome strikes again.

This is the thing that drives this forecaster crazy, and sometimes it seems like the dome actually exists. But I have a theory why this happens.

It’s the balconies’ fault…pun intended

The Balcones Fault line runs from the Dallas/Fort Worth area southwest through Waco, Temple, and Austin and then west through San Antonio to Del Rio. It is the route that I-35 takes through central Texas.

The error can be easily seen in the visible true-color satellite image circled in red. It forms the eastern border of the Texas Hill State and the western border of the Texas Coastal Plain.

(NOAA)

To the west, the land is at a much higher elevation and falling rapidly, as shown in this geographic section.

(Utah Austin Bureau of Economic Geology)

Elevation change is most pronounced in Travis County along the Colorado River.

(Utah Austin Bureau of Economic Geology)

So what’s going on with the storms here?

In most cases, strong and severe thunderstorms are rooted to the surface. This means that storm flow is generated at ground level and rises into the storm. But as storms move through western Travis County, the bottom drops as the line reaches the fault zone.

This results in a sudden interruption in storm flow and the storms weaken quickly. But as the storm line reaches the eastern part of the county, it reshapes the surface flow and intensifies quickly.

It is not an invisible rain dome but a microscopic geographical phenomenon.

This drives me crazy.

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