2013: May 31 El Reno, OK EF-5 is Widest Tornado On Record

[Shawn Schuman]

Normally that's the way it works, but I'm pretty certain the width was based on radar in this case.

Edit, here's part of the PNS:

PUBLIC INFORMATION STATEMENT...CORRECTED
NATIONAL WEATHER SERVICE NORMAN OK
1206 PM CDT TUE JUN 4 2013

...UPDATE ON MAY 31 EL RENO TORNADO...

METEOROLOGISTS WITH THE NATIONAL WEATHER SERVICE AND RESEARCHERS FROM
THE UNIVERSITY OF OKLAHOMA AND THE CENTER FOR SEVERE WEATHER RESEARCH
CONTINUE TO INVESTIGATE INFORMATION RELATED TO THE MAY 31 EL RENO
TORNADO.

WITH THIS INVESTIGATION... THE TORNADO HAS BEEN UPGRADED TO AN EF5
TORNADO BASED ON VELOCITY DATA FROM THE RESEARCH MOBILE RADAR DATA
FROM THE UNIVERSITY OF OKLAHOMA RAXPOL RADAR AND THE DOPPLER ON
WHEELS RADARS FROM THE CENTER FOR SEVERE WEATHER RESEARCH. IN
ADDITION... THE WIDTH OF TORNADO WAS MEASURED BY THE MOBILE RADAR
DATA TO BE 2.6 MILES AFTER THE TORNADO PASSED EAST OF US HIGHWAY 81
SOUTH OF EL RENO. THIS WIDTH IS THE WIDTH OF THE TORNADO ITSELF AND
DOES NOT INCLUDE THE DAMAGING STRAIGHT-LINE WINDS NEAR THE TORNADO AS
DETERMINED BY THE HIGH-RESOLUTION MOBILE RADAR DATA. THE 2.6 MILE
TORNADO PATH WIDTH IS BELIEVED TO BE THE WIDEST TORNADO ON RECORD
IN THE UNITED STATES.

 

[Patrick Marsh]

Listening to the OUN Webinar, the width was determined to be the 65mph contour in the radar data. 65mph is the minimum windspeed in the EF-Scale.

 

[Shawn Schuman]

Thanks Patrick. If that's the case, I don't know what to make of the 1999 Mulhall tornado.

 

[Caleb Chevalier]

Wow, that's quite something. Thanks for the insight.

 

[MClarkson]

If you assume a 2.6 mile diameter 1km tall cone, with wind speeds on average 100mph inside of it, you're looking at ~10^13 Joules of kinetic energy (from .5*m*v^2). Choose your own values and check me, also depends on if you assume uniform, rankine (truncated at some radial distance), etc. The first atomic bomb was ~1/10th that in terms of energy released. Note this is not the amount of work applied to the surface for destruction.

I also get about 1e13 joules for each vertical km of such a monster. I see 5e13J for little boy over Hiroshima, making this twister 5x weaker if you just count the tornado kinetic energy (assuming its 1km tall), and not the entire latent heat of the thunderstorm, which is much bigger.

 

[Paul Schmit]

If you assume a 2.6 mile diameter 1km tall cone, with wind speeds on average 100mph inside of it, you're looking at ~10^13 Joules of kinetic energy (from .5*m*v^2). Choose your own values and check me, also depends on if you assume uniform, rankine (truncated at some radial distance), etc. The first atomic bomb was ~1/10th that in terms of energy released. Note this is not the amount of work applied to the surface for destruction.

Perhaps beyond just static energy considerations, there's an important dynamic power consideration as well. Rapid, unsustainable intensification would be characterized by a sudden spike in dE/dt (the time rate of change of the energy content of the vortex), not necessarily by the total energy content of the vortex at any given moment (just like slamming on the brakes and going from 5mph to 0 in a vehicle produces a much more violent jolt on the body compared a slower easing of the brakes going from, say, 100mph to 95mph...it's the time rate of change that produces the most vivid effect on the observer). From reading the reports about the El Reno tornado's ground speed and change in trajectory during the occlusion process, it's likely that the vortex-relative inflow nearly doubled as the ground speed increased from 25mph to 40+mph, meaning the flow rate of primed, unstable air into the vortex region nearly doubled. In that case, the vortex structure can either spin up faster and maintain the same physical configuration to account for the increased flux of buoyant energy, or it can expand physically and redistribute its energy content (which way it goes is likely governed by other environmental constraints). And if the vortex expands physically, then it becomes a bigger target for incoming air parcels (so intensification in response to changes in vortex motion could easily be a nonlinear process). One could even go further and analyze the distribution of potential energy *density* in the inflow, rather than just the total numbers. The occlusion process could more efficiently focus and direct the buoyant streamlines directly into the vortex, with fewer streamlines diverted around the vortex into the ambient mesocyclone, thus increasing further the flux of energy directly into the surface-based vortex itself and forcing further expansion and redistribution of the total vortex energy content to accommodate the enhanced vortex-relative energy flux. To put it simply and qualitatively, it's got to be a combination of subtle geometric effects associated with the distribution of inflow near the surface (as dictated by things like the RFD gust front) and the overall vortex-relative motion within an environment primed with a rich supply of high SBCAPE air.

Not being directly involved in tornado research myself, I wonder if there's been any thought given to the idea of enhancement of effective inflow theta-e due to mixing and entrainment of moisture-laden, completely saturated RFD air parcels by sub-saturated storm-relative inflow. Maybe for some vertical soundings one could find a way to combine surface parcels with LCL parcels in such a way that increases overall |dtheta-e/dz|, while other soundings would be more prohibitive. If some action of the RFD increases (at least locally) the effective inflow theta-e relative to the ambient theta-e above the surface, then CAPE is amplified locally and another intensification mechanism would be present.

Just random musings of a physicist wishing he were working on something else right now...