Dr. Rob Carver's WunderBlog

Hermine brings life-threatening flooding to central Texas

Posted by: Dr. Rob Carver, 09:03 GMT le 08 septembre 2010

The remnants of Tropical Storm Hermine are producing significant amounts of rain, causing dangerous flooding in central Texas. As of 300 AM CDT, radar data (Fig. 1) estimates that over 15 inches of rain as fallen over Travis and Williamson county. This is a result of storms from Hermine passing over the same area, this is known as training.

Fig. 1 Storm-total precipitation from the New Braunfels NEXRAD at 300AM.

To make matters worse, the rain is falling directly over the Balcones Escarpment, a sharp transition between low coastal plains and the higher Edwards Plateau. This rapid change in elevation promotes flash-flooding. That is going on in Georgetown, TX. Figure 2 shows a graph of the height of the San Gabriel river. According to this graph, the river rose 16 feet in under 6 hours.

Fig. 2 Height of the San Gabriel River near Georgetown, TX. Image courtesy of the USGS.

The USGS webpage indicates that this is a 97.86% event, that is to say only 2.14% of time will the river flow more than it is now. Roughly speaking, this is a 50 year flood for Georgetown.

I haven't been able to find news reports, but here's what the NWS has to say:
Areas along I-35 and the Balcones Escarpment in and around the Austin Metro area will experience a life threatening flash flood event over the next several hours. Numerous evacuations and high water rescues have already been reported by the media and law enforcement personnel.

Historical Comparisons

The city of Austin has a good summary of flash floods. However, the reference storm for central Texas is the Thrall rainstorm of September 9-10, 1921. Remnants from a tropical storm stalled out over Williamson County and produced record amounts of rainfall. The official records was 20 inches in a 12-hour period, but an unofficial rain gage 2 miles north of Thrall, TX recorded 32 inches of rain in a 12-hour period. The resulting flooding was catastrophic. There was $19 million in damage and officially 215 fatalities. _Road, River and Ol'Boy Politics_ by Linda Scarbrough has a chapter on the human impact of the flood in the context of discussing how Williamson County sought to get two dams built. There's a comprehensive meteorological review of the flood in Monthly Weather Review.

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Late Night Thoughts on Earl and Fiona

Posted by: Dr. Rob Carver, 09:28 GMT le 31 août 2010

I'm going on evening blog duty Tuesday night to help Jeff M. with Earl as he makes his approach towards the East Coast. For me at least, it's really hard to discuss a meteorological situation cold. I need to develop situational awareness and get a feel for how the models are doing. So, time to practice. EarlSo far, Earl's behaving like your arch-typical Cape Verde hurricane. He's big, strong (Cat 4), and headed for the US after doing some damage to the Caribbea...

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The Great Russian Heat Wave of July 2010

Posted by: Dr. Rob Carver, 22:53 GMT le 05 août 2010

The July 2010 heat wave for western Russia, including Moscow, is one of the most impressive heat waves I've ever seen. I thought it would be instructive to look at the meterological conditions to understand what creates heat waves and droughts. Fig. 1 Meteorological history of July 2010 for Sheremetyevo International Airport, Moscow, Russia. Theory of Drought The most immediate cause for drought/heat waves are upper-le...

Updated: 17:13 GMT le 13 Mars 2012

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Severe Weather in the Northern Plains

Posted by: Dr. Rob Carver, 06:30 GMT le 19 juin 2010

There's been notable severe weather in the northern Plains and Midwest over the past two days. I'll start by discussing the severe storms that went through the Midwest.June 18As of 930 PM PDT, there were 2 tornado reports, 51 hail reports, and 317 reports of damaging straight-line winds. The strongest wind report I saw was 90 mph at La Porte, Indiana, and the airport weather station at Haines, MI reported a wind gust of 79 mph. Here is a plot of the storm reports...

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Tornadoes in northern Oklahoma, May 19, 2010

Posted by: Dr. Rob Carver, 09:41 GMT le 20 mai 2010

It was a busy day for the Storm Prediction Center and NWS Forecast offices in Texas and Oklahoma on May 19. There were 25 tornado reports, 8 reports of damaging winds, and 23 hail reports (The largest reported was 3.25 inches). Preliminary news reports suggest there was one injury associated with the severe weather when a tractor-trailer rig was blown over by winds. Of the NWS offices responsible for Oklahoma, Norman issued 24 tornado warnings, Amarillo 16, and T...

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