The atmosphere seems to be on track for a pretty volatile Sunday across parts of the south, with a moderate risk (4 on a scale from 1-5) for severe weather across the Arklatex region. This could be the first major outbreak of the year, with a few large, violent tornadoes possible.
Models are consistently showing a good mixture of instability and wind shear that should create supercell thunderstorms in and around the moderate risk area, which will be able to produce very large hail, damaging winds, and significant tornadoes.
There's an index called the Energy Helicity Index, or EHI, that takes into account both the amount of instability in the atmosphere as well as the potential rotation that could develop in a thunderstorm. These two ingredients combined could create supercells that produce tornadoes.
Under the right set of atmospheric conditions, EHI values of 1-2 are sufficient to produce tornadic supercells, and EHI values of 3-4 are enough to help spawn violent tornadoes (EF-3 or stronger).
Last night's run of the NAM model is spitting out EHI values greater than 6 across parts of Arkansas and Louisiana on Sunday morning and afternoon. Given that storms are likely in the region of high EHI values, some violent, long-track tornadoes are possible.
The SPC mentioned that they might raise portions of Arkansas and Louisiana to a rare high risk for severe weather in their 12:00 PM CDT outlook. If you rank the threat for severe weather on a scale from 1 to 5, a high risk is a 5.
Keep a very close eye on developments if you live in these areas, and make sure you have a plan in case you're threatened by dangerous weather.
Here are some links to help you keep track of the forecast.
- The Storm Prediction Center is the official agency in charge of predicting severe thunderstorms in the United States.
- The National Weather Service issues local forecasts, as well as severe thunderstorm/tornado warnings across the U.S.
- Wunderground provides excellent weather radar imagery — click on the + closest to your location.
- NASA's website provides excellent satellite imagery from the GOES weather satellites.
- Dr. Greg Forbes of The Weather Channel is a world-class meteorologist who developed the accurate TOR:CON index that evaluates the threat for tornadoes on a 0-10 scale. His TOR:CON forecasts are found on weather.com.
[Images via SPC and TwisterData]