KTAB Your Weather Authority

Update to Severe Thunderstorm Warnings – includes new ‘Damage Threat’ Categories

Weather

ABILENE, Texas (KTAB/KRBC) – Severe weather is something we have all experienced here in the Big Country. Severe thunderstorms can be life-threatening, but not all of them are the same. Hazardous conditions that can be experienced in severe storms range from flash flooding, cloud to ground lightning, straight line winds, large hail, and tornadoes. So recently, the National Weather Service has made some adaptations to better convey the severity of the potential impacts from thunderstorm winds and hail to the public. They have added a “damage threat” tag to severe thunderstorm warnings. The two new damage threat categories are “Destructive” and “Considerable”.  

For a storm to receive the destructive category, it must have at least 2.75-inch diameter(baseball-sized) hail and/or 80 mph winds. When a storm reaches one or both of these criteria, it will automatically activate a Wireless Emergency Alert (WEA) on all smartphones within the warned area.  

For a storm to receive the considerable category, it must have at least 1.75-inch diameter (golf ball sized) hail. This damage threat category will not trigger a WEA.  

While these two new categories have been created, the criteria for baseline or “base” severe thunderstorms have not been changed. A storm is considered severe if it has 1 inch (quarter-sized) hail and/or 58 mph winds. Baseline is not considered a damage threat tag, so if a severe thunderstorm warning does not have a tag present, damage is expected to be at the base level.  

On average, only 10 percent of all severe thunderstorms reach the destructive category across the nation each year. Most storms that receive the destructive category are damaging wind events, like derechoes, and some of the larger, more intense thunderstorms called supercells which can typically produce very large hail. This new destructive category will help convey to the public that urgent action is needed.  

This can serve as a good reminder for all of us to make sure all emergency alerts are turned on for our phones, especially as we move into the unofficial second severe weather season here in the Big Country. September and October usually bring us a second push of severe weather opportunities for a few reasons.  

The first is that the jet stream begins to dip down a bit further. The jet stream is located about 5 to 9 miles above the Earth’s surface in the mid to upper troposphere and can help provide lift to storms to continue to develop.  

The next is that in September and October, we can start to see early season cold fronts. In front, along, and even behind these frontal boundaries we can see thunderstorm activity. Early season cold fronts can act as a catalyst to severe weather formation.  

We also tend to see an increase in upper-level disturbances in these months. An upper-level disturbance is a very broad meteorological term and usually describes a disruption in the upper atmospheric flow pattern. These are typically associated with clouds and precipitation and are characterized by distinct cyclonic flow, a pocket of cold air, and even a jet streak, which is an area of stronger winds located in the jet stream. All of these atmospheric features make the air more unstable and conducive to clouds and precipitation.  

The Big Country also seems to have more available moisture in these months. We tend to see winds from out of the southeast, acting as a good transport mechanism for gulf moisture. Air is considered unstable in the lower layers of the atmosphere when the air is warmer and or more humid than surrounding air. When the environment is unstable, the weather can change suddenly, and lead to formation of severe storms.  

And lastly, we have a higher possibility of seeing remnants of hurricanes and tropical storms from the Gulf of Mexico. The peak of hurricane season for the Texas coast is between August and September. One example was seen on Columbus Day, October 12th, 1981, when remnants of Hurricane Norma brought 20” of rain and lots of flooding to the Big Country.  

While summer is on its way out the door, we cannot let our guard down when it comes to severe weather. It is important for all of us to stay vigilant and informed about the weather throughout the next couple of months. 

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