Severe Weather Threat for Saturday


The quiet weather pattern that has occurred across much of the U.S. the last couple of weeks looks to get more active. A severe weather risk area has been defined for Saturday and Saturday Night by the Storm Prediction Center. Areas included in the risk area includes much of eastern Texas, southeast Oklahoma, west Arkansas, and far west Louisiana. For this particular blog post, two things are noted. We will be using the 12z GFS run from today. Also, we will focus on Saturday’s severe weather risk.

12z GFS Surface Based CAPE Hr 90

With the amount of Surface Based Instability shown here (less than 1,000 J/kg), it may not seem like it is enough. Now that we are into the month of December, it usually does not take much surface based instability to cause a ruckus.

12z GFS Surface Dewpoint Hr 90

One thing we always look for in particular is the available amount of moisture. With this setup, plenty of moisture is available for thunderstorm development. Note the dewpoints in the 40s Saturday Night across central and west Texas. Also, note the dewpoints well into the 60s across eastern Texas. This will prove to be the zone for the severe weather potential.

12z GFS 850 Winds Hr 90 12z GFS 500 Winds Hr 90 12z GFS Surface Winds Hr 90

Note the surface winds to the south and southeast, while compared to the 850 mb (5,000 feet above ground level), and 500 mb (18,000 feet above ground level). While there is not a significant amount of difference in the changing of the wind direction, it is more than sufficient for any thunderstorm that develops to produce damaging straight-line winds, along with a tornado threat.

12z GFS 1km Helicity Hr 90 12z GFS 3km Helicity Hr 90

The amount of helicity in the lowest one (greater than 100 units) and three kilometers (greater than 250 units) Saturday Night are more than sufficient for any thunderstorm, whether along the squall line, or ahead of it, to have some tornado potential.

12z GFS 1km AGL Shear Hr 90 12z GFS 6km AGL Shear Hr 90

Plenty of shear in the lowest one kilometer (noted in the yellow), along with the lowest six kilometers (in the yellows and oranges), are noted on this run of the GFS. When combined with the amount surface based instability being forecast, this has the looks of a low CAPE/high shear setup.

12z GFS SBCIN Hr 90

This particular run of the GFS does not indicate any of the Surface Based Inhibition (also known as the “cap”) late Saturday Night. Storms that do develop will have a better opportunity to sustain themselves Saturday Night.

12z GFS 1km VGP Hr 90 12z GFS 1km EHI Hr 90

While the one kilometer Energy Helicity Index and Vorticity Generation Parameter are not particularly high, that in itself can be deceiving. This particular storm setup is a cool season type setup, which is more typical for this time of year.

SUMMARY : The potential is there for severe thunderstorms Saturday Night across the risk area. While damaging straight line winds will be the main severe weather hazard, a tornado risk can not be ruled out either. We will keep you up to date with the latest. Stay tuned.


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