The weather radar conference is ongoing in Colorado this week, and one of the conference papers features some eye-popping statistics regarding the 31 May El Reno tornado. This paper, authored by Josh Wurman and others, is titled “Preliminary Results from the ROTATE-2013 Season”. Now, for the facts …

Near Highway 81, the El Reno tornado achieved a peak forward motion of 55 mph! This is comparable to the highest translational velocities of tornadoes ever observed by the Doppler on Wheels (DOWs).

After the tornado crossed Highway 81, the sub-vortices (smaller tornadoes) within the larger circulation grew to mammoth proportions. The largest were bigger than the size of 3 football fields combined! (Most parent tornadoes do not reach this size!)

As the tornado approached Highway 81, small vortices developed on the northwest side of the circulation and “fed” the circulation. Similar vortex behavior was noted with the gigantic Seward, Kansas tornado (23 May 08).

The tornado displayed vortices on multiple scales, similar to matryoshka dolls. This “tornado within a tornado” behavior was noted shortly before the tornado crossed 81. At that time, the tornado had two prominent vortices: an inner vortex, about 150 yards in width; and an outer vortex, about 1.25 miles in diameter. Wurman notes this behavior in other large tornadoes, including the Kellerville, Texas (8 June 95) and Harper, Kansas (12 May 04) tornadoes.

One of the most intense sub-vortices during the El Reno tornado translated at an incredible 180 mph! Curiously, this sub-vortex was also stationary at times during its 2 minute life-span.

At 6:26 p.m., the DOWs measured a 255 mph gust in a sub-vortex just south of Interstate 40. This exceeds the EF5 threshold by over 50 mph.

Given the fast translation of this sub-vortex, a stationary observer would have only experienced these maximum winds for 0.5 seconds. Talk about acceleration!

Applying a theoretical model (Rankine vortex) to the tornado yields velocities between 290 and 330 mph! Of course, this assumes the theory is a good model of the real atmosphere (among other caveats) – but still, it’s very impressive.

Officially listed at 2.6 miles in diameter, the El Reno tornado is the largest tornado on record. But it might also be the largest tornado ever documented. Using the 30 m/s wind threshold (and excluding the rear-flank downdraft winds), the tornado was an unbelievable 4.3 miles wide!! (Even using a 50 m/s threshold yields a 3.1 mile wide tornado … unbelievable!) For comparison, this is larger than the Mulhall tornado (3 May 99), which was the previous standard-bearer for behemoth tornadoes (2.8 miles in diameter using the 30 m/s threshold). EDIT: The 4.3 mile width in the paper refers to the parent circulation of the tornado, not necessarily the tornado itself. It should also be noted that the 4.3 mile width was > 300 feet above ground level, not necessarily corresponding to the size of the tornado.



In addition to the gigantic cyclonic tornado, the El Reno storm simultaneously produced a strong anti-cyclonic tornado. This tornado featured powerful sub-vortices (potentially, the first ever documented) with winds peaking around 145 mph!

(Here is my video of the El Reno tornado.)