Tuesday, January 29, 2013

Severe Weather Update for Texas...

Thunderstorms are developing southward into extreme northwest Texas along the cold front at this hour:

...and I expect them to increase in coverage and intensity and sweep through most of northcentral and northeast Texas this afternoon...including the DFW Metroplex region.  Damaging wind gusts and hail will be the primary threats, although an isolated tornado spin-up cannot be ruled out.

If any isolated storms are able to develop and become organized ahead of this line, the localized tornado threat would increase with such cells.

Further South, including the Austin-San Antonio corridor along I-35, its coming down to a battle of the atmosphere.  The low levels are very moist and will become increasingly unstable throughout the day, however a relatively strong "capping inversion" (also known as a "lid" - see the oldie but goodie link for details) is in place across the region.

Strong instability and increasing support from the upper level storm approaching from the West is likely to be able to overcome the cap and allow for thunderstorm development down at least part of the I-35 corridor later this afternoon... but the question is how far South?

One way to measure how unstable it is in the lower atmosphere is to look at an index called CAPE (convective available potential energy).  The current CAPE analysis shows high values starting to "pool" along the dryline in west-central and southwest Texas, as indicated by the green shaded area on the image below:

This pocket of instability is forecast to move Eastward into the Austin-San Antonio corridor and become even more unstable later this afternoon, as indicated by the brighter yellow shaded area on the forecast image below (valid at 3pm):

This could indeed be enough of a "push" to allow for thunderstorm development as far South as the Austin-San Antonio area late this afternoon.

As I've been saying for a few days now... this is one of those "all or nothing" situations.  If a storm is able to break through the cap and form in this region, it will tap that high instability and could become severe quickly, with large hail, damaging winds and an isolated tornado possible.

I would place the chance of a thunderstorm at 30-40% in Austin, 20-30% in the Kyle/Buda areas, and 20% in San Antonio.  If a storm is able to form in any of those areas, the chance of severe weather would be relatively high, so stay alert!

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