Friday, May 11, 2007

"Tornado Follow-up: Greensburg, KS EF-5"

Basically, they don't get any bigger or any nastier, level 5 tornadoes. The former scale was the "Fujita" scale which would make the Greensburg tornado an F-5...now the National Weather Service uses an "enhanced Fujita" scale that is a bit more accurate with respect to a new set of more detailed damage parameters...which this one still easily ranks EF-5. FYI, there hasn't been a confirmed F-5/EF-5 in the U.S. since the Bridge Creek/Moore, OK F-5 on May 3, 1999 (where specialized instruments recorded wind speeds up to 318 mph - the map below shows that whole outbreak)...click to enlarge...


Below is a fascinating, if not chilling, radar grab from the National Weather Service in Dodge City, KS, moments before it hit Greensburg. For any of us in severe weather mode with rotating cells, you are co
nstantly checking scans of "relative velocity"...Doppler radar, among other things, measures wind direction and speed, how fast air is moving toward or away from the radar. Those two directions are given the opposing red and green colorations...where there might be a vortex forming, even if aloft and not at the surface, you will see specific orbs of red and green up against each other, what we refer to as a 'couplet'. Mind you, there is a skill to interpreting radar imagery, but for the purpose at hand this will get you where we're going...


(click on the pic to enlarge) I have circled the couplet of the EF-5 and put an arrow on Greensburg's map dot. Next, take note of the color-keyed bar at the top left...note the red-green break in the center...and then notice the colors extending farther left and right (greater velocity)...now compare the colors with what you see in the EF-5 couplet...the white range extends into turquoise and even a little blue, and the red's into whitish pink and even orange...at the vortex you have orange up against blue...a rare sight on screens that surely had the NWS folks swallowing hard, for such a tornado is guaranteed to come with death certificates if it hits civilization.


Next, look at the aerial coverage map of the tornado swath...moving up from left to right...hitting Greensburg, momentarily lifting only to touch right back down with a destructive path almost 2 miles wide...honestly, while tornado knowledge has increased by leaps and bounds, there is still a lot we don't know about these behemoth cells, mainly because there are so few of them to study. Their immense size creates wind speeds well in excess of 200 mph, far in excess of any Atlantic hurricanes...and within their ultra-wide 'wedge' funnels...well, something else may be at work.

Think Norelco 3-head electric razor...you know, the one the 3-D animated Santa rides over snowy hills and has for decades on TV ads at Christmas?...there is some thought that the super large tornadoes may actually be multiple vortices working in concert with each other like a giant buzzsaw...like the 3 Norelco heads rotating in the same circle. The average tornado path width is less than one-quarter of a mile, and this one approached being 8 times wider than that...over 10,000 feet wide...at least 33 football fields end to end...

TGIF - carpe diem, everybody!

4 comments:

Anonymous said...

Great explanation in "layman's terms", Bob --- thanks for sharing! Yeah, the "orange and blue together" part of the couplet is what can make a Met choke back tears.
The awesome power of nature is very humbling indeed ..... and all the more reason to "carpe diem"!

Suzy :)

Bob Child said...

I saw an interview with Jay Leno, who has quite the extensive classic car and motorcycle collection...when asked which was his favorite, he said, "The blue one." Simple can be a good thing!

Anonymous said...

Those images were awesome and at the same time, terrifying. The couplet being much bigger than the dot that represents Greensburg was really a scary site. Didn't understand all you said, but you insights were much appreciated.
lori

Bob Child said...

Glad you got some use out of the post. Radar interpretation is not that easy and cut-and-dried...anyway you cut it, it was one monster of a storm for the record books!