Rating Tornado Intensity Based on Moblie Radar

[BrandonHeadley]

I see a few potential problems with mixing damage reports and DOW readings. IMHO we should be using any and all methods to better understand the damage caused by tornadoes.

The first would be standardizing on when to use data from DOWs. Say one office decides to consider radar data only when it impacts rural areas and another decides to use it every time there is a tornado report. This could cause a skew in the data from a certain office. Also, if a DOW indicated a EF3, but the damage survey indicated EF4 damage then which do you go with? Let's say the damage survey found EF2 damage but a DOW indicated EF4 wind speeds who decides what it should be rated? I see the potential for the higher rated to be given every time which causes the data to be skewed toward more violent tornadoes.

Second, DOWs can't be everywhere. As someone already brought up Tornado Alley has a large concentration of them during peak time. This obviously makes sense monetarily and for the research they are doing. The more tornadoes they get in a shorter amount of time the more data they have. However, it may bias reports to more violent tornadoes in tornado alley vs other parts of the country.

Finally, I hear a lot of Media reports that there are more violent tornadoes now then __ years ago. I believe this is at least somewhat because of the change from F-scale to EF-scale. Additionally this can be attributed to the increase in research and data gathered during the storms. The data gathered isn't a bad thing at all and the more data we gather the better we understand what causes a tornado or doesn't cause them. I would urge people/media to be careful when comparing the violence of tornadoes from year to year.

Just my thoughts on the matter. I do think the NWS should look into some standards. Who knows maybe they already have them in place.

 

[rdale]

Brandon, if DOW shows EF4 winds and the damage did not match the DI listed in the EF Scale, it more likely means that the DIs are incorrect. I'll take an actual measurement over a hypothetical damage determination any day of the week,

 

[Brian McKibben]

I think if this trend continues, we might find that there are a lot more violent tornadoes than what the databases say. I wouldn't doubt both the Rozell and Bennington were violent. They sure did look like beast. I still wish we could see some radar data from the KFOR south Moore doppler from the May 20th tornado. It was 3 miles away from EF-5 damage, so no telling how strong the winds were as measured by radar.

 

[Jeff Duda]

I think if this trend continues, we might find that there are a lot more violent tornadoes than what the databases say. I wouldn't doubt both the Rozell and Bennington were violent. They sure did look like beast. I still wish we could see some radar data from the KFOR south Moore doppler from the May 20th tornado. It was 3 miles away from EF-5 damage, so no telling how strong the winds were as measured by radar.

Can't thinko f the reference right now (check SLS conference proceedings from 06-08 or EJSS) but I believe Wurman et al. already did such a study using the database of DOW-sampled tornadoes and found that EF1 and EF2 tornadoes were much more common than had been previously measured by just damage surveys. It had been thought that the tornado intensity distribution was more of an inverse exponential (i.e., of the form y = exp(-x)) so that the most common tornado rating was EF0. This new evidence suggests there is more of a gamma distribution (i.e., a bell curve skewed right - with a heavy right tail) to fit the intensity ratings to be consistent with EF1/EF2 tornadoes being more common.

 

[Shawn Schuman]

Can't thinko f the reference right now (check SLS conference proceedings from 06-08 or EJSS) but I believe Wurman et al. already did such a study using the database of DOW-sampled tornadoes and found that EF1 and EF2 tornadoes were much more common than had been previously measured by just damage surveys. It had been thought that the tornado intensity distribution was more of an inverse exponential (i.e., of the form y = exp(-x)) so that the most common tornado rating was EF0. This new evidence suggests there is more of a gamma distribution (i.e., a bell curve skewed right - with a heavy right tail) to fit the intensity ratings to be consistent with EF1/EF2 tornadoes being more common.

I think you're referring to:

Curtis R. Alexander and J. Wurman, 2008: Updated mobile radar climatology of supercell tornado structures and dynamics, Proceedings 24th Conference on Severe Local Storms, Savannah, GA, American Meteorological Society

 

[Jake Orosi]

I think all technology that increases the accuracy of the measurement should be used. One should simply keep in mind that the older tornado records have less reliable/fewer observations.

I tend to agree.

Tornadoes are typically EF-rated based on damage, true; but remember the whole point of that: the extent of the damage is used as a gauge to estimate wind speeds which are usually extremely local and therefore not measured by actual instruments that were not in the path of the tornado. Certain wind speeds are expected to cause a certain severity of damage. It's exactly like using the Beaufort scale when you don't have an anemometer.

I think that, wherever actual scientific instruments have a confirmed reading, we should absolutely defer to them when assigning the EF-rating of a tornado. And of course, where such data aren't available, we should continue to measure as best we can using observed structural damage. That's not bias; it's merely being as accurate as possible on a case-by-case basis. There's no such thing as tornado being "unfairly" rated "only" an EF-4 based on actually-measured wind speed for instance when in somebody's opinion it "should have been an EF-5", or vice-versa. It is a wind-speed classification; no more or less.

 

[rdale]

El Reno went from EF3 to EF5 based on mobile Doppler radar...

 

[James Gustina]

They also updated the width, 2.6 miles wide. Beats out Hallam by .1 for widest tornado ever.

 

[Brian McKibben]

Saw that too Rob. Also, it looks like it has overtaken the Hallam NE as the widest.

Gary England ‏@garyeOK3m
El Reno, OK tornado now rated EF5, Doppler measured 296 mph. Largest ever documented: 2.6 miles wide. gary

 

[Brian McKibben]

Moving at 30 mph at 2.6 miles wide means tornado winds for 5.2 minutes.

 

[Stan Rose]

Bear in mind that the winds were presumably measured in the suction vortex, whcih was a tiny fraction of the width of the main circulation.

 

[truechampion]

According to the EF scale, an EF5 is winds of more than 200 mph. Most EF5's are officially rated around 210 mph. This is the second tornado I know of in which the wind speed was measured at or near 300 mph. It seems like the old F-scale was more accurate.

I know the wind speed was measured a short distance above the ground, but I don't think there would be that dramatic of a difference in the wind speed at ground level.

 

[Brian McKibben]

In one of my previous post I wondered if any mobile radars sampled the Moore storm on 5/20. I just got back word that unfortunately they did not sample that tornado. It would have been a great data set to compare others against.

 

[Shawn Schuman]

According to the EF scale, an EF5 is winds of more than 200 mph. Most EF5's are officially rated around 210 mph. This is the second tornado I know of in which the wind speed was measured at or near 300 mph. It seems like the old F-scale was more accurate.

I know the wind speed was measured a short distance above the ground, but I don't think there would be that dramatic of a difference in the wind speed at ground level.

It's not that the old scale was more accurate, it's just that various instances of EF5-level damage can be caused by wind speeds in the ~200mph range. The scale is open-ended to account for the fact that some tornadoes may be well above that mark. If you check the various DIs and the wind speed ranges associated with each DOD, you'll get a better sense of it.

 

[Ryan Difani]

As some have stated I think that rating tornadoes by mobile radars is a good thing as I have little doubt that it is far more accurate in determining the wind speeds within a tornado than a damage based estimate especially in rural areas where to tornado caused little to no damage. As comes better technology we should use it. I do have issues with it however... if we have for years used a damage based estimate and we now use measured wind speeds from radar on occasion we will likely create a bias in tornado strength climatology, especially so as mobile radar ratings become more frequent. 20 years from now when we are reviewing tornado strength since records began, 2013 may show up as a year that starts a spike in more intense tornadoes solely because we have rated so many by mobile radars this year. We'll be looking back wishing we could make some more accurate comparisons between damage rated tornadoes and mobile radar rated tornadoes.

I'm not suggesting that we not use these radars for rating but rather I suggest that we also note the damage survey results as well in our climatological records for comparisons sake. Using a satellite remote sensing analogy (I'm a GIS guy), when new technologies with better satellite resolutions come along it is certainly used but the older satellite with less resolution is still used so that the two satellites can be calibrated to each other. With this calibration satellite images from 2013 can be directly compared to satellite images from 1983 despite the change in resolution (with resolution: the accuracy of the the data). I suggest that the NWS/SPC/NCDC also record the damage indicated ratings as well for a fair comparisons sake. Thus the Rozel, KS tornado would be noted as an EF-2 by damage, EF-4 by mobile radar... similarly the El Reno tornado would be noted with both an EF-3 and EF-5 ratings (along with other tornadoes rated by mobile radar). Maybe a new scale other than EF should be used for a rating based on mobile radars?

These are just my humble opinions and I hope that we do find some way of keeping or noting these rating scale differences in tornado climatology records for sake of future research. I understand the EF-Scale has flaws but no matter the flaws we need a way of comparing a older more flawed rating to a newer less flawed rating.