ABC13 Meteorologist Elyse Smith explains the weather pattern that led to the catastrophic flooding event in central Texas this weekend.

Central Texas witnessed one of its worst flood events on record during a busy holiday weekend.

The combination of heavy rainfall and the hilly terrain led to the extreme rise in rivers and a Flash Flood Emergency. The Guadalupe River in particular rose over 20 feet in less than 30 minutes, where the National Weather Service in Austin/San Antonio had to warn of a “large and deadly flood wave” moving down the river.

On Monday, ABC13 Meteorologist Elyse Smith broke down the weather pattern that brought the catastrophic flood to central Texas.

Showers and storms began to develop across central Texas around midnight on Friday, July 4. These storms produced heavy rains with potential rainfall rates of upwards of 3 inches an hour. A sign that deep, tropical moisture was overhead. In fact, these storms were able to tap into moisture from the remnants of once hurricane Flossie from the Pacific, tropical storm Barry in the Atlantic, and a low-level jet that pulled in high moisture levels from the Gulf.

SEE ALSO: ABC13 meteorologist looks into timeline of weather alerts issued in central Texas flooding

ABC13 Meteorologist Elyse Smith analyzed when weather alerts were issued in the hours leading up to the flood and as it unfolded early morning on the Fourth of July.

Storms exploded early Friday morning in size and number, where eventually the combination of the existing storms and tropical moisture overhead allowed for an area of low pressure to develop in the mid-levels of the atmosphere. This is called a Mesoscale Convective Vortex, or MCV. And what’s key about this MCV developing where it did is that there was nothing else in the weather pattern around Texas to move it. This allowed the storm system to stall, leading to more rounds of heavy rain and flooding across the region for several days.

While Mesoscale Convective Vortexes are more common across the Midwest and Plains, they can develop anywhere when conditions are right. A Mesoscale Convective Vortex is known for producing torrential rain and can even lead to strong thunderstorms with gusty winds and lots of lightning. Typically, these systems move with the jet stream. But in this case, the jet stream that would supposedly usher this system out of the state was too far north.

Another factor to consider with this flood was the region where the heavy rain fell.

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Authorities said the death toll was sure to rise as crews looked for many people who were missing.

Central Texas has coined the nickname “Flash Flood Alley” because of its history of devastating floods. Many recall this flood as the worst the region has seen since the Flood of 1987. A big reason is the topography and terrain of central Texas. It’s both hilly with changing elevation, and the ground beneath the soil is limestone. Limestone, as Chief Meteorologist Travis Herzog calls it, is like “natural cement.”

When heavy rainstorms move over the region, the rain rushes across the landscape as excessive runoff, which can fill local rivers, creeks, and streams quickly. And the high volume of rain can then lead to rushing floodwaters, as seen in this flood on the Fourth of July. In all, this Mesoscale Convective Vortex that led to this catastrophic flood event is an example of how efficient and extreme Mother Nature can be when conditions are right.

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