Last week, I discussed some interesting examples of violent (EF-4/5) tornadoes, and I am going over them again for a different reason. This time, some cases will be explored a bit in regards to controversy with whether a tornado in question should be rated EF4 or 5.
Before going further, it is important to note that Enhanced Fujita takes damage done to buildings or objects in the account, and the damage supposedly represents a three-second gust, according to Storm Prediction Center. The weakest tornadoes are usually rated EF0 at 65-85 mph while the most powerful tornadoes are rated EF5 with winds over 200 mph.
To give a little more context, 28 categories of damage indicators are used in EF scale. Some examples are hardwood trees, institutional buildings and small retail buildings, like McDonalds. Also, there were a few cases in the past that radar measurements were added in consideration if the tornado in question stayed in an open field or its strength was unclear due to lack of sturdy buildings in an area of complete destruction or weaker buildings and trees.
Revisiting the case of Smoky Mountains EF4 from NWS Morristown archive, there were a few interesting aspects to how it was rated. Since it struck in open wilderness with no well-constructed buildings.
The electrical tower that was flattened into the lake was the only man-made structure affected by the tornado. There were plenty of hardwood and softwood tree species in the park. Based on the table of damage indicators on SPC website, the upper limit for debarking hardwood trees was 167 mph although the expected wind speed for debarking hardwood trees was 143 mph, below EF4 threshold.
It was almost exactly the same for a collapsed metal truss tower like the one at the lake, thus lending the tornado the original EF3 rating. However, the tree damage was more extreme than what was normally expected for EF3 tornado despite around 70 mph forward speed, so its rating was upgraded to EF4.
In his journal article, one researcher who conducted a tree study in damage path pointed out that more specific estimation of strength remained ambiguous, and it was possible that the tornado was EF5 strength, more powerful than previously thought. At the end of the day, it was still unclear whether the tornado was EF4 or EF5 because metal truss tower and trees could be easily demolished by EF3, and there were not any well-constructed buildings in the path to give a better idea of its strength.
Regarding 2011 Tuscaloosa EF4, there were shades of gray between EF4 and EF5 damages. Going back to the EF scale, both EF4 and EF5 damage usually featured well-constructed buildings that were completely leveled and cars that were thrown, according to The Weather Channel.
However, the key differences between EF4 and EF5 were whether the debris remained around the place of origins or swept away. In the case of EF4 damage, the debris and vehicles tend to stay close to places of origins. For the tornado to earn EF5 rating, well-constructed buildings have to be not just flattened but also be swept away, and vehicles had to be thrown at least 100 meters.
Back to Tuscaloosa tornado, there was a pressure for EF5 rating for the tornado, and some of the damages it caused were borderline on EF5, but it was determined that the tornado was a high-end EF4 with winds of 190 mph, according to Extreme Planet.
This was where a huge flaw in EF scale came in. The scale itself placed a huge emphasis on damage done by the tornado itself rather than wind duration. Thus, the Tuscaloosa tornado did not cause enough damage to qualify for definite EF5 rating, yet the author of Extreme Planet article argued that the tornado was likely as powerful, if not more, than larger and slower-moving EF-5 tornadoes.
The author pointed out that the tornado and many others from that day were moving at highway speeds (50-70+ mph), giving each tornado up to a few seconds to do the worst damage. Therefore, the four confirmed EF5 tornadoes from same day were likely more powerful than most of the other 5-rated tornadoes, but the duration of maximum winds were less than five seconds due to their fast forward speed as the author pointed out.
With that in mind, nearly-stationary 2013 Bennington, KS EF4 twister was a very different beast. As mentioned in my previous article, the radar measured the 247 mph winds, but the damage was minimal because it stayed over an open farm field for the whole lifespan.
Imagine 200+ mph winds for 15 minutes at least. Theoretically, Bennington tornado could have caused far more intense damage than fast-moving 2011 Hackleburg, AL tornado even though they both were very powerful. Basically, that was comparing less than 2 mph to upwards of 70 mph. I felt that storm motion should be considered when rating tornadoes.
Again with Bennington, I strongly argued that mobile radar data could be supplemented to help determine the strength of a tornado if it stayed over an open field or hit only trees, metal truss towers or weak buildings. That was a similar situation for Rozel EF-4 from my previous article.
I would also argue using it if it moved very slowly because its strength was less clear, but the tornado was over an area for the longer duration. However, 2013 El Reno tornado was one of few tornadoes that I know of whose radar data was excluded from consideration for EF strength. According to NWS Norman, mobile radar measured ~300 mph winds in some of smaller vortexes inside 2.6 miles wide behemoth, but the EF rating was downgraded from EF5 to EF3 due to lack of well-constructed building for intense vortexes to hit.
At the end of day, tornadoes were far more complex than the EF scales showed. Maybe one day they should add few more things into consideration: motion speed, lack of structures and mobile radar data.
I am a trained storm spotter and I spent years studying meteorology in my free times. Those blogs reflect my opinions on weather-related topics with some light humor and commentaries.