August 2009 Archives

"I live in the Star Ranch subdivision near Hutto. Last night the storm was short, but severe. Hail and very strong twister like winds blew down my fence on both sides along with my neighbor's play house and patio furniture. It also picked up their big trampoline and it landed three houses away. My garage doors seemed to suck in and out." - Lynn Bryan

We know severe wind gusts over 65 mph tore up homes and businesses in Hutto and Taylor a couple of nights ago, but were those wind gusts the result of a microburst or a tornado?

What happened in Hutto was a severe downburst wind event. They often happen very quickly and without much warning. Below you will see a couple of images I found to help explain a microburst. This is the same type of an event that brought down the Cowboys practice bubble up in Irving back in May.

It is the same event that brought down Delta Flight 191 as it attempted to land at DFW International Airport on August 2, 1985. Sadly, 8 crew and 126 passengers lost their lives in that crash, but it was essential in the development of windshear detection equipment that keeps airplanes in safer environments today.

A downburst (or microburst) is a different process than a tornado, but severe wind damage is easily seen in both situations. Heavy rain-cooled air rushes down out of the base of the thunderstorm. Research has shown that melting of hail can play an important role in downburst formation. The rainshaft and winds in a microburst smash into the surface of the earth and spread outward from the point of impact. Hutto and Taylor were likely at that point of impact where winds were upwards of 65 mph.

In these pictures from the National Oceanic and Atmospheric Administration below, notice the surface curl soon after a microburst impacted the area. It is a real world example of the schematic above.

One of the things the meteorologists at our local National Weather Service offices are trained to do is observe damage patterns after severe wind events. The patterns can help determine and support what processes might have been occurring at the time the damage was sustained.

The swirling and chaotic winds in a tornado will leave strikingly different damage patterns than straight-line wind or microburst events. Since the wind spreads outwards in all directions, the wind regime in a microburst is opposite to that of a tornado.

The environment prior to thunderstorm development is also very important. Our atmosphere this time of year is not as favorable for tornado development, due to the lack of upper level wind support.

We need strong upper level winds moving from southwest to northeast and low level winds out of the southeast to create a rotating thunderstorm updraft. As that rotating updraft grows taller and turns faster, a tornado can spin up at the surface. We most often see this along strong cold fronts in the spring.

Scattered thunderstorms that we see over the next couple of days, will be in a favorable environment for severe downburst or microburst winds. As in the case of Hutto and Taylor, no severe thunderstorm warning was in effect at the time of the microburst. They can happen suddenly and with very little warning, so keep an eye to the sky the next couple of days.

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Thank you, thank you from the bottom of my heart! I appreciate everyone who made a donation. Thanks to the volunteers, too, who gave their time and sweat to make this year's For the Children school supply drive a huge success.

Distribution Day was this last Saturday at Sanchez Elementary School in southeast Austin. Administrators and employees from at least 10 area districts came by to load up supplies for the start of the school year next week.

The Besy Buy #204 volunteer team. From left to right: Dani, Jessica, Claudia, Meghan, Mandy, Meliza, Liza

Thanks to your generosity, we were able to provide supplies to over 50,000 students from K to 4th grade. It was the 20th year For the Children has been working hard to see that area school children succeed right from the very first day of class. Since 1989, For the Children has helped over 363,000 students in Central Texas.

For the Children is an all-volunteer non-profit organization, so 100% of all cash donations go to the purchase of school supplies. Since it can buy in bulk, For the Children can really make that dollar stretch!

Under $4.00 can supply one child. $20 can supply 6 students.

Area H-E-B stores made a huge difference this year with the $1, $3 and $5 scan cards. Thank you H-E-B for all of your help. We hope to partner with you again next year!

Volunteers: Zach Vasquez and his Dad and For the Children President, Xavier, along with Narda Hurt and Julie Miller

Volunteers: Debbie de Haas, Simon Eastwood and Luis Gutierrez

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Ready for a little late summer fireworks? Earth is entering into a trail of dust from the Comet Swift-Tutle and the debris can give us quite a light show each year.

We will be in the densest part of this dust on Wednesday, August 12th. The best time for viewing will be late Tuesday night into the pre-dawn hours that Wednesday morning. At it's peak, this year's Perseid shower could produce 100 meteors per hour.

We might have to deal with a few morning clouds that day, but sky conditions should be pretty good. There will be some bright light from a 55% Gibbous moon.

For more information, check out NASA's website or take a look at this article in the Los Angeles Times.

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