The Moore Tornado

By: 24hourprof , 3:23 PM GMT on May 28, 2013

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On Tuesday, May 21, in the aftermath of the EF-5 tornado that devastated Moore, Oklahoma, the previous day, I watched Dr. Greg Forbes of The Weather Channel give a live interview standing in front of some of the damage. At the time, the media referred to the twister as an EF-4 tornado, but Dr. Forbes pointed to a heavy propane tank that had been ripped from its moorings and then thrown a distance of a quarter mile, providing evidence, Dr. Forbes stated, that supported a rating of EF-5. The damage survey by the National Weather Service later confirmed Dr. Forbes' assessment, officially upgrading the tornado to EF-5 (it appears that the National Weather Service based their rating on the damage to one of the schools (photograph below).


EF-5 damage at one of the schools in Moore, OK, struck by the killer tornado on May 20, 2013. Courtesy of the National Weather Service.

The issue with the airborne propane tank at Moore, Oklahoma, reminded me of the F-5 tornado that struck Wheatland, Pennsylvania, and the Ohio towns of Newton Falls and Niles on May 31, 1985. The F-5 tornado was one of a swarm of twisters over parts of the eastern Great Lakes region and southern Canada on this date (tornado tracks). I remember the F-4 tornado that rapidly knocked down thousands of trees in Black Moshannon Park (north of State College, Pa.), shaking the ground so much that "tremors" registered on seismometers on the campus of Penn State about 20 miles away. At any rate, Dr. Forbes' statement about the propane tank thrown a quarter mile in Moore, OK, reminded me of the 1985 outbreak because, while ripping through Niles, Ohio, the F-5 twister crumbled and tossed large storage tanks as it they were plastic play toys (see photograph), qualifying as F-5 damage.

I will never forget the depth of the human tragedy inflicted by the Moore tornado. I was also deeply saddened by the suffering of animals hurt and killed by the tornado (I cannot really bring myself to look at this photograph). As a scientist, I will remember the rapid intensification of the parent supercell's low-level mesocyclone (in other words, rapid mesocyclogenesis) and the resulting rapid intensification of the Moore tornado.

The goal of my blog today is to focus on the rapid intensification of the supercell's low-level mesocyclone in the hopes of giving you a better sense for why the supercell's tornado intensified so quickly.

The bulk vertical wind shear between the ground and an altitude of six kilometers was more than sufficient for supercells to develop on May 20 (radar loop, courtesy of SPC). To get a better sense of bulk shear and its role in determining thunderstorm mode (type), please review my previous blog on the tornado that struck Granbury, Texas, on May 16, 2013. Although the bulk shear between the ground and six kilometers favored supercells, the low-level wind shear in the lower troposphere was not particularly impressive on this day. As it turns out, the magnitude of the low-level wind shear plays a role in tornadogenesis. Let's investigate.

Storm-Relative Helicity


Spin around a horizontal axis (a streamline drawn parallel to the storm-relative inflow of the supercell) gets tilted into the vertical by a convective updraft, paving the wave for a rotating updraft. Courtesy of Jessica Higgs

Remember the annotated photograph of a supercell (shown above) that I've already highlighted in a couple of my blogs? By way of review, low-level vertical wind shear helps to create the spin around the horizontal orange line. By convention, the orange horizontal line represents a streamline of the storm-relative wind. By definition, the storm-relative wind is the observed wind vector minus the storm-motion vector. In plainer language, we can think of the storm-relative wind as the movement of air relative to a stationary storm (the storm is moving, of course, but we can better visualize the storm-relative wind by imagining the storm at a standstill). So the horizontal orange line you see in the image above indicates the storm-relative inflow, which ultimately gets tilted into the vertical by a developing convective updraft. The bottom line here is that the spin around the orange horizontal streamline (drawn parallel to the storm-relative wind) gets tilted into the vertical, creating the rotating updraft (mesocyclone), which is the hallmark of the supercell. For the record, the spin around the horizontal streamline for the storm-relative inflow is called streamwise vorticity. Again, streamwise vorticity is induced by low-level wind shear, which brings us back to the Moore tornadic supercell.

To a large degree, the strength of a supercell's mesocyclone depends on the rate at which the rotating updraft "ingests" streamwise vorticity. In this context, you can think of the mesocyclone ingesting streamwise vorticity as Lee slurping up spinning spaghetti noodles at the dinner table ("Grenci" is Italian). How's that for visualization!! One way to measure the rate at which a supercell ingests streamwise vorticity is storm-relative helicity (SRH). Essentially, storm-relative helicity is computed by multiplying the magnitude of the storm-relative inflow (the speed at which Lee slurps up his spaghetti noodles) multiplied by the magnitude of the streamwise vorticity (how fast the air is spinning about the local horizontal storm-relative streamline). Then we simply add up all the contributions from the ground to a designated altitude in the boundary layer (usually one kilometer or three kilometers). Ladies and gentlemen, I give you storm-relative helicity.


The 18Z Rapid Refresh model analysis of storm-relative helicity from the ground to an altitude of one kilometer. Courtesy of the Storm Prediction Center.

Check out the 18Z Rapid Refresh model analyses of the surface-to-one-kilometer storm-relative helicity (above) and the surface-to-three-kilometers storm-relative helicity on May 20, 2013 (before the supercells were initiated in central Oklahoma; see the 19Z mosaic of composite reflectivity and compare to the 18Z mosaic of composite reflectivity). Both RR analyses indicate that, at face value, the pattern was not screaming out any loud message that supercells capable of spawning severe tornadoes were imminent. That's because the threshold values above which forecasters start to pay closer attention to supercells spawning tornadoes are 100 square meters per square second (for sfc-1 km storm-relative helicity) and 250 square meters per square second (for sfc-3 km storm-relative helicity). Representative SRH values in central Oklahoma before storm initiation were in the neighborhood of 80-90 square meters per square second (for sfc-1 km storm-relative helicity) and 125 to 150 square meters per square second (for sfc-3 km storm-relative helicity). Yes, supercells were likely (the magnitude of the vertical wind shear between the ground and an altitude of six kilometers was large), but there were no screaming messages that an outbreak of supercellular tornadoes was imminent (possible, yes, but not written in stone).

Storm Merger

So how could the mesocyclone associated with the Moore supercell rapidly intensify the way it did? In other words, how did the already rotating updraft spin faster? Keep in mind that we've already established that the low-level wind shear was not really noteworthy in the pre-storm environment. There are a couple of additional factors we should consider. While reading my account, keep in mind that, according to the National Weather Service, the tornado formed at 1945Z (2:45 P.M. CDT) and dissipated at 2035Z (3:35 P.M. CDT).


The 1946Z (2:46 P.M. CDT) base reflectivity (left) and storm-relative velocities (right) from the Doppler radar at Oklahoma City (KTLX). Larger image. Courtesy of NOAA.

First, the hook echo of the Moore supercell initially was not very impressive. To see what I mean, check out, above, the two-panel radar image from the Oklahoma City Doppler Radar at 1946Z on May 20 (2:46 P.M. CDT; larger image). That's base reflectivity (BR) on the left and storm-relative velocities (SRV) on the right (larger image). Note the "hook" on the reflectivity panel and the rather "modest" velocity couplet marking the position of the rotating updraft (mesocyclone). Also note the more diminutive thunderstorm south of the Moore supercell. In a very short time, this smaller storm merged with the Moore supercell (1951Z BR and SRV; 1955Z BR and SRV; 1959Z BR and SRV). By 2003Z (3:03 P.M. CDT), the hook echo was much more pronounced and the mesocyclone had rapidly intensified (see the 2003Z two-panel BR and SRV below; larger image). Indeed, the circulation associated with the mesocyclone was dramatically stronger (very strong inbound and outbound velocities). More importantly, there was a debris ball on the base reflectivity, indicative that there were non-meteorological airborne targets with high reflectivity. In other words, the tornado associated with the rapidly intensifying mesocyclone had also rapidly strengthened and was ripping and tossing debris into the air. Just five minutes later at 2008Z (3:08 P.M. CDT), the debris ball was even more dramatic as the tornado entered Moore (two-panel image).


The 2003Z (3:03 P.M. CDT) base reflectivity (left) and storm-relative velocities (right) from the Doppler radar at Oklahoma City on May 20, 2013. By this time, a smaller thunderstorm had merged with the Moore supercell and its mesocyclone had undergone rapid intensification. The tornado had also intensified...note the debris ball on the reflectivity panel. Larger image. Just five minutes later at 2008Z (3:08 P.M. CDT), the debris ball was even more dramatic as the tornado entered Moore (two-panel image). Courtesy of NOAA.

When thunderstorms merged, there was a marked increase in low-level convergence and the corresponding low-level vorticity (spin around a local vertical axis). In effect, the air column housing the mesocyclone stretched vertically and increased the spin (check out the first half of this copyrighted flash animation from Penn State's online certificate program; note how horizontal convergence, vertical stretching, and increase spin about a vertical axis go hand in hand). Lesson learned: Merging thunderstorms likely played a role in the rapid intensification of the low-level mesocyclone associated with the Moore tornado. I point out that there was also a merger of thunderstorms during the initial phases of the tornado that devastated Joplin, Missouri, on May 22, 2011.

Ingesting Vorticity from the Synoptic-Scale Front

The second factor that might have played a role in the rapid intensification of the low-level mesocyclone was that the Moore supercell ingested low-level vorticity associated with the stationary front. To get a sense for the bigger picture, check out the 18Z (2 P.M. CDT) surface analysis and the 19Z mosaic of composite reflectivity. Obviously, the stationary front helped to initiate severe storms in Oklahoma. Keep in mind that fronts lie in pressure troughs and that the wind shift that typically marks the position of fronts helps to produce convergence. Let's revisit the first part of the copyrighted flash animation from Penn State's online certificate program that connects the concepts of convergence and vorticity (spin about a vertical axis in this case). Revisit the 18Z surface analysis and compare it to the 18Z Rapid Refresh model analysis of 1000-mb absolute vorticity below (1000 mb is a proxy for the surface; larger image). Can you pick out the position of the stationary front? Yes, the stationary front coincided with the elongated maximum of absolute vorticity. Given that the Moore supercell was initiated along the stationary front, a reasonable question to ask is whether the storm ingested vorticity associated with the front.


18Z The Rapid Refresh model analysis of 1000-mb absolute vorticity on May 20, 2013. Units are expressed in 10^-5 seconds^-1. Note the elongated maximum in vorticity along the stationary front (18Z surface analysis). Larger image. Courtesy of Penn State.

Whether the complete explanation of the rapid mesocyclogenesis inside the Moore supercell involves both the merging of thunderstorms and the ingestion of vorticity from the stationary front (or some other factors such as instability, moisture, etc.) will likely result from future studies. My blog is only meant to help to stimulate discussion among my faithful Wunderground readers.

Whatever the answers, it was a storm that never will be forgotten in central Oklahoma.

Stay safe, my friends.

Lee

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39. hackmon1
3:59 PM GMT on June 28, 2013
Very, very interesting. Thank you.
Member Since: June 13, 2011 Posts: 0 Comments: 1
38. WunderAlertBot (Admin)
5:55 PM GMT on June 05, 2013
24hourprof has created a new entry.
37. 24hourprof
1:26 PM GMT on June 05, 2013
Quoting weathergeek5:
Cannot wait for your write up on the may 31st tornado. It's official: The El Reno, OK tornado from last Friday has been upgraded to EF-5 with mobile radar measured winds of over 290 mph and a max width of 2.6 miles. This makes it the world record now for the widest tornado ever recorded!

The old record that was broken was from Hallam, NE back on May 22, 2004 with a width of 2.5 miles.


Man, it's just unbelievable.

The recent outbreaks of extreme tornadoes in Oklahoma is consistent the climatological probabilities for significant tornadoes on May 31 (and other days in late May and early June; see below; larger image).

Member Since: October 24, 2012 Posts: 94 Comments: 826
36. weathergeek5
5:12 PM GMT on June 04, 2013
Cannot wait for your write up on the may 31st tornado. It's official: The El Reno, OK tornado from last Friday has been upgraded to EF-5 with mobile radar measured winds of over 290 mph and a max width of 2.6 miles. This makes it the world record now for the widest tornado ever recorded!

The old record that was broken was from Hallam, NE back on May 22, 2004 with a width of 2.5 miles.
Member Since: December 25, 2005 Posts: 0 Comments: 1744
35. 24hourprof
6:27 PM GMT on June 02, 2013
Quoting Barefootontherocks:
Good morning, Lee.
Thanks for writing this blog. And the diagram you posted at 26 makes more sense to me than any other I've seen on supercell structure. Maybe because it jives with what I've seen in the sky. Thanks for that also. Surely the effects of storm merger on supercells is an area ripe for research.

Also, something I noted that day that's possibly related to the modeled low level helicity. The watch on Monday, May 20, 2013 included a moderate risk for tornadoes and a low risk of EF2-plus. The day before, when a (preliminarily rated) EF4 occurred in Norman and points east, the EF2plus watch risk was moderate but I'm not sure of the modeled setup. Goes to show, where tornadoes are concerned, there is much research work to be done. Maybe, in the end, we'll learn all their secrets. In a way, I hope not.

On the subject of tornado formation, thought you might enjoy this: Early researchers' "Tornado machines" and more.


It just goes to show you how we forecasters can get humbled by the atmosphere. And, over the years, I've had my own share of busts.

On the bright side, there has been great advancement in the science since I was in graduate school circa 1980, but there are still a lot of unsolved problems...an open challenge that I always tried to stress to my students.
Member Since: October 24, 2012 Posts: 94 Comments: 826
34. Barefootontherocks
2:22 PM GMT on June 02, 2013
Good morning, Lee.
Thanks for writing this blog. And the diagram you posted at 26 makes more sense to me than any other I've seen on supercell structure. Maybe because it jives with what I've seen in the sky. Thanks for that also. Surely the effects of storm merger on supercells is an area ripe for research.

Also, something I noted that day that's possibly related to the modeled low level helicity. The watch on Monday, May 20, 2013 included a moderate risk for tornadoes and a low risk of EF2-plus. The day before, when a (preliminarily rated) EF4 occurred in Norman and points east, the EF2plus watch risk was moderate but I'm not sure of the modeled setup. Goes to show, where tornadoes are concerned, there is much research work to be done. Maybe, in the end, we'll learn all their secrets. In a way, I hope not.

On the subject of tornado formation, thought you might enjoy this: Early researchers' "Tornado machines" and more.
Member Since: April 29, 2006 Posts: 157 Comments: 19214
33. Barefootontherocks
2:07 PM GMT on June 02, 2013
Quoting bappit:
It wasn't too hard to find this paper by Charles A. Doswell III, Cooperative Institute for Mesoscale Meteorological Studies Norman, Oklahoma when I searched for "streamwise vorticity": "A Primer on Vorticity for Application in Supercells and Tornadoes"

It has lots of interesting discussion and illustrations. For instance, for streamwise vorticity it shows:



For crosswise vorticity it has:



Lots of other interesting stuff:

"What we call "touchdown" of a tornado is actually an intensification of the vortex at the ground, which can be viewed as a clustering of the vortex lines. Nothing material is actually coming down as the tornado "touches down" ... this process might more properly called a "spin-up" or "surface intensification." The intense part of a vortex aloft can build both upward and downward ... Apparently, tornadic vortices can intensify first at the surface and then build upward. After some time period, Fig. 15 could evolve into something resembling Fig. 14; that is, it also can evolve into a tornado through a deep layer. Thus, the intensified vortex that we call a tornado might be seen to develop upward from the surface, downward from aloft, or both upward and downward."
This is interesting, especially in light of the chaser videos that surfaced Friday eve, May 31 - the ones of the "carousel" of dancing vortices that occurred in the El Reno, OK tornado that day under that huge cloud of circulation. Of course, I don't really know and probably at this point science doesn't either, what the connection is with ground or low level helicity and vorticity, but my gut tells me there is one. I hope scientists do more research into these secrets.
Member Since: April 29, 2006 Posts: 157 Comments: 19214
32. bappit
10:26 PM GMT on May 30, 2013
It appears that in the streamwise vorticity diagram there are arrows showing winds vearing with height. The axis of the vorticity appears to be parallel to the winds above the lowest layer of the atmosphere--or am I looking at this wrong?

If I am looking at the diagram from the Doswell paper correctly, then that would seem to match what appears in the Wikipedia diagram (though the cartoon of a cb in the background at this stage is misleading).

Member Since: May 18, 2006 Posts: 10 Comments: 6147
31. bappit
10:15 PM GMT on May 30, 2013
It wasn't too hard to find this paper by Charles A. Doswell III, Cooperative Institute for Mesoscale Meteorological Studies Norman, Oklahoma when I searched for "streamwise vorticity": "A Primer on Vorticity for Application in Supercells and Tornadoes"

It has lots of interesting discussion and illustrations. For instance, for streamwise vorticity it shows:



For crosswise vorticity it has:



Lots of other interesting stuff:

"What we call "touchdown" of a tornado is actually an intensification of the vortex at the ground, which can be viewed as a clustering of the vortex lines. Nothing material is actually coming down as the tornado "touches down" ... this process might more properly called a "spin-up" or "surface intensification." The intense part of a vortex aloft can build both upward and downward ... Apparently, tornadic vortices can intensify first at the surface and then build upward. After some time period, Fig. 15 could evolve into something resembling Fig. 14; that is, it also can evolve into a tornado through a deep layer. Thus, the intensified vortex that we call a tornado might be seen to develop upward from the surface, downward from aloft, or both upward and downward."
Member Since: May 18, 2006 Posts: 10 Comments: 6147
30. 24hourprof
12:29 PM GMT on May 30, 2013
Quoting weatherhistorian:
Another great blog Lee! WU is so fortunate to have you join our 'blogosphere'.

One thing about violent tornadoes (EF-4 and EF-5s) I've always been curious about is how lightning frequency is associated with these rare events. I'll never forget the night of June 7, 1984 when Barneveld, Wisconsin was swept away by an F-5 twister (sadly, along with 9 lives). I lived in Madison at the time and will never forget the astonishing light show that occurred that night when the twister roared through Barneveld (about 20 miles to our west). The lightning, for about a 15 minute period, became so frequent that it resembled a strobe light--impossible to differentiate between one flash and another-- and then suddenly ceased almost entirely. The following day (and after visiting the Met. lab at UW) I realized that the minutes of frequent lightning apparently preceded the tornado's formation and that once the storm had fully formed, the lightning rate suddenly decreased.

I know this is a bit 'off subject', but am curious if you are aware of any connection between lightning and violent tornado formation.


Hi Chris,

You are very kind to say those things about my blog. I am lucky that Wunderground gave me this opportunity.

I'm no expert on lightning, but here's what I know. This is the basic model for the distribution of electrical charges in a "generic" thunderstorm that I used in class at PSU (courtesy of, and copyright by, the Penn State online certificate program).

As it turns out, the relative positions of positive and negative flashes around supercells can depart markedly from the generic model you just saw. For example, the image below shows the two-kilometer radar reflectivity and the distribution of lightning flashes around the supercell that spawned an F4 tornado at Spencer, South Dakota, on May 30, 1998.



The distribution of positive and negative lightning flashes around the supercell that spawned an F4 tornado near Spencer, South Dakota, on May 30, 1998 (between 0146:30Z and 0151:30Z). The colored areas represent radar reflectivity at 0149Z at approximately two kilometers.

It is interesting to note that positive CG flashes occurred near the echo cores of high radar reflectivity, while negative CG flashes were detected near the peripheries of (low-to-moderate) radar reflectivity.

The timing of this outburst of positive flashes makes this case even more compelling because the F4 tornado was ripping through Spencer at this time.

Prior to this event, research had suggested that supercells dominated by positive lightning flashes produced a violent tornado after the frequency of CG positive flashes peaked (during a lull in positive CG flashes or a transition to negative flashes). The Spencer supercell was clearly an outlier. Indeed, its maximum frequency of positive CG flashes (and the relative percentage of positive CG flashes) dramatically increased as the F4 tornado started to rip through Spencer. This account serves to humble us with the recognition that there%u2019s still a lot more to learn about lightning. And that includes me!!

I'll try to get some lightning data for the Moore supercell and present it here.

Thanks for the great question. I hope I did it some justice.
Member Since: October 24, 2012 Posts: 94 Comments: 826
29. Christopher C. Burt , Weather Historian
1:51 AM GMT on May 30, 2013
Another great blog Lee! WU is so fortunate to have you join our 'blogosphere'.

One thing about violent tornadoes (EF-4 and EF-5s) I've always been curious about is how lightning frequency is associated with these rare events. I'll never forget the night of June 7, 1984 when Barneveld, Wisconsin was swept away by an F-5 twister (sadly, along with 9 lives). I lived in Madison at the time and will never forget the astonishing light show that occurred that night when the twister roared through Barneveld (about 20 miles to our west). The lightning, for about a 15 minute period, became so frequent that it resembled a strobe light--impossible to differentiate between one flash and another-- and then suddenly ceased almost entirely. The following day (and after visiting the Met. lab at UW) I realized that the minutes of frequent lightning apparently preceded the tornado's formation and that once the storm had fully formed, the lightning rate suddenly decreased.

I know this is a bit 'off subject', but am curious if you are aware of any connection between lightning and violent tornado formation.
Member Since: February 15, 2006 Posts: 316 Comments: 296
28. 24hourprof
10:26 PM GMT on May 29, 2013
Quoting carsoncityweather:
Thanks Lee for the great post. It's nice refresher and shows a great conceptual model for storm-relative helicity. I like the spaghetti analogy.

Thanks a million.

Robert - From the milli-bar.


Many thanks, Robert!!!!

Yeah, I've always liked the spaghetti-noodle analogy for teaching the tilting of spin around a horizontal axis into the vertical (by a convective updraft).

Again, thanks Robert.

For readers who don't know Robert, he was a great student of mine in the Penn State online certificate program.
Member Since: October 24, 2012 Posts: 94 Comments: 826
27. carsoncityweather
10:22 PM GMT on May 29, 2013
Thanks Lee for the great post. It's nice refresher and shows a great conceptual model for storm-relative helicity. I like the spaghetti analogy.

Thanks a million.

Robert - From the milli-bar.
Member Since: February 1, 2012 Posts: 0 Comments: 10
26. 24hourprof
10:19 PM GMT on May 29, 2013
Quoting Globe199:
Just a fantastic post. I'm starting to get a handle on how tornadoes form. This post is pretty technical, and I think I need to read it a couple more times to fully grasp it, but great job. That flash animation of convergence and divergence helps a ton.

I'm still not fully clear on vorticity and helicity. Maybe you can help me here. I'm looking at the Jessica Higgs picture. How are the convective updraft (vertical flow) and the horizontal flow connected? In other words, does (or WHY does) the updraft draw in air from along a single horizontal axis? That is, why does the updraft not just suck air from a radial (i.e., circular) area? Is this a dumb question?

It was my understanding that wind shear creates horizontal rotation and that something causes that rotation to "tip" vertical, causing a mesocyclone. Is that incorrect or just oversimplified?

Thanks again for such a detailed and thoughtful analysis.


No questions are "dumb." It simply means that you want to learn, and that's fantastic.

Actually, the Jessica Higgs diagram shows only one "spaghetti noodle" (a storm-relative streamline) when there actually are many...to show them all would confuse. You'd need enough spaghetti noodles to adequately represent the entire storm-relative inflow...see the circled pinks on the panel displaying the storm-relative velocities below:



The 2012Z base reflectivity (left) and storm-relative velocities (right) on May 20, 2013, from the radar near Oklahoma City.

The spin around the horizontal storm-relative streamline wouldn't change unless it encountered a sustained convective updraft. So that explains how the horizontal spin gets tilted into the vertical.

With regard to your question about the extent of the circulation, perhaps this plan view of a supercell would help you. Focus your attention on the yellow, storm-relative streamlines. In many ways, the circulation around the mesocyclone (resembles the circulation of the synoptic-scale low-pressure systems you see on weather maps on the six o'clock news. By the way, "T" marks the position of the tornado, and the curved, reddish-filled area is the rotating updraft (the mesocyclone).



Copyrighted by the Penn State online certificate program.

And remember that you learn a little more each time you think about a concept.

Hope this helps. And thanks for the encouragement. This old man needs it!
Member Since: October 24, 2012 Posts: 94 Comments: 826
25. Globe199
5:11 PM GMT on May 29, 2013
Just a fantastic post. I'm starting to get a handle on how tornadoes form. This post is pretty technical, and I think I need to read it a couple more times to fully grasp it, but great job. That flash animation of convergence and divergence helps a ton.

I'm still not fully clear on vorticity and helicity. Maybe you can help me here. I'm looking at the Jessica Higgs picture. How are the convective updraft (vertical flow) and the horizontal flow connected? In other words, does (or WHY does) the updraft draw in air from along a single horizontal axis? That is, why does the updraft not just suck air from a radial (i.e., circular) area? Is this a dumb question?

It was my understanding that wind shear creates horizontal rotation and that something causes that rotation to "tip" vertical, causing a mesocyclone. Is that incorrect or just oversimplified?

Thanks again for such a detailed and thoughtful analysis.
Member Since: May 15, 2002 Posts: 1 Comments: 55
24. 24hourprof
11:42 AM GMT on May 29, 2013
Quoting pcola57:
Thanks for the outstanding explanation Lee..
The noted Images of radar and meso scale map really helped me understand..
Thank you for your excellent post..


Very kind. And you're quite welcome.

Member Since: October 24, 2012 Posts: 94 Comments: 826
23. pcola57
11:40 AM GMT on May 29, 2013
Thanks for the outstanding explanation Lee..
The noted Images of radar and meso scale map really helped me understand..
Thank you for your excellent post..
Member Since: August 13, 2009 Posts: 13 Comments: 6911
22. 24hourprof
11:13 AM GMT on May 29, 2013
Quoting snotly:
Well, yes. Extreme low level vorticity is a tornado.


I have no idea what your point is. Synoptic-scale vorticity and the vorticity associated with a mesocyclone are not even close to the vorticity associated with a tornado.

Quoting snotly:
Nice view on the satellite how the dry line is forcing the updraft over the top and to the left. Basically the atmosphere is given a nice chance to equalize itself. Then the upper level wind is acting like a soda-straw pulling the updraft in as the tops are blown off.


Upper-level winds do not act like a soda straw. That's a pretty unscientific analogy in my view.
Member Since: October 24, 2012 Posts: 94 Comments: 826
20. 24hourprof
11:54 PM GMT on May 28, 2013
Quoting weathergeek5:
Thanks for this learning!!! I thank you for the hard work it takes to write these up!!


You're too kind, but I confess it's a labor of love.
Member Since: October 24, 2012 Posts: 94 Comments: 826
19. 24hourprof
11:53 PM GMT on May 28, 2013
Quoting wx74008:
I worked at KJRH-TV in Tulsa, OK during the Tulsa-Catoosa tornado in April 1993. That supercell struggled to produce a tornado as it crossed the northern parts of Tulsa until a small thunderstorm collapsed to its SW. In fact, the collapsing thunderstorm produced a microburst causing severe damage to a church at 15th and Memorial about 5 miles SW of the supercell. Chief Meteorologist Gary Shore and I believe the downburst then fed into the mesocyclone which then rapidly produced an F-4 tornado. The tornado was totally wrapped in heavy rain as it moved due east on I-44 killing most of the victims in their cars. I will never forget how the storm on radar went from a ragged appendage to a "pirate's hook" on radar within seconds. I am a firm believer that low-level vorticity is perhaps the biggest component of tornadogenesis.


Great post! Many thanks for contributing.

Lee
Member Since: October 24, 2012 Posts: 94 Comments: 826
18. weathergeek5
10:51 PM GMT on May 28, 2013
Thanks for this learning!!! I thank you for the hard work it takes to write these up!!
Member Since: December 25, 2005 Posts: 0 Comments: 1744
17. wx74008
9:39 PM GMT on May 28, 2013
I worked at KJRH-TV in Tulsa, OK during the Tulsa-Catoosa tornado in April 1993. That supercell struggled to produce a tornado as it crossed the northern parts of Tulsa until a small thunderstorm collapsed to its SW. In fact, the collapsing thunderstorm produced a microburst causing severe damage to a church at 15th and Memorial about 5 miles SW of the supercell. Chief Meteorologist Gary Shore and I believe the downburst then fed into the mesocyclone which then rapidly produced an F-4 tornado. The tornado was totally wrapped in heavy rain as it moved due east on I-44 killing most of the victims in their cars. I will never forget how the storm on radar went from a ragged appendage to a "pirate's hook" on radar within seconds. I am a firm believer that low-level vorticity is perhaps the biggest component of tornadogenesis.
Member Since: April 26, 2007 Posts: 1 Comments: 1
16. 24hourprof
9:16 PM GMT on May 28, 2013
Quoting weathergeek5:
Are there any papers that delve into storm mergers?


Great question. Being a diehard Penn Stater, I'll refer you to the second poster presentation at the 2012 AMS conference by one of our PSU graduate students...his topic seems to fit the topic at hand perfectly. I'd contact Ryan directly.

Hope this helps.
Member Since: October 24, 2012 Posts: 94 Comments: 826
15. 24hourprof
9:09 PM GMT on May 28, 2013
Quoting georgevandenberghe:
I'll concur this is an interesting post.  Severe weather is not a specialty
of mine so I'm in pure learning mode on this one.


That's about the only aspect you don't know, George. You're a fountain of meteorological knowledge!
Member Since: October 24, 2012 Posts: 94 Comments: 826
14. georgevandenberghe
7:27 PM GMT on May 28, 2013
I'll concur this is an interesting post.  Severe weather is not a specialty
of mine so I'm in pure learning mode on this one.
Member Since: February 1, 2012 Posts: 19 Comments: 2079
13. weathergeek5
6:20 PM GMT on May 28, 2013
Are there any papers that delve into storm mergers?
Member Since: December 25, 2005 Posts: 0 Comments: 1744
12. 24hourprof
6:12 PM GMT on May 28, 2013
Quoting weathergeek5:
How does this tornado compare to the mesocyclogenesis of the Joplin tornado? I remember with that one, two storms merged together too.


They were both rated EF-5, and, yes, there was a storm merger relatively early on the Joplin supercell's life cycle.
Member Since: October 24, 2012 Posts: 94 Comments: 826
11. weathergeek5
6:07 PM GMT on May 28, 2013
How does this tornado compare to the mesocyclogenesis of the Joplin tornado? I remember with that one, two storms merged together too.
Member Since: December 25, 2005 Posts: 0 Comments: 1744
10. 24hourprof
6:02 PM GMT on May 28, 2013
Quoting StormPro:
Thanks Lee...taught me a lot today


You're quite welcome. Very kind of you to say that.
Member Since: October 24, 2012 Posts: 94 Comments: 826
9. 24hourprof
6:01 PM GMT on May 28, 2013
Quoting KEEPEROFTHEGATE:
I watch it from start to finish

and I knew I was seeing something amazing and deadly

wunder of nature





Those are very sobering satellite loops. Many thanks for your contribution.
Member Since: October 24, 2012 Posts: 94 Comments: 826
8. StormPro
5:06 PM GMT on May 28, 2013
Thanks Lee...taught me a lot today
Member Since: August 4, 2010 Posts: 0 Comments: 606
7. KEEPEROFTHEGATE (Mod)
4:54 PM GMT on May 28, 2013
I watch it from start to finish

and I knew I was seeing something amazing and deadly

wunder of nature



Member Since: July 15, 2006 Posts: 176 Comments: 55605
6. 24hourprof
4:49 PM GMT on May 28, 2013
Quoting NewBerlinTX:
Very informative post. Thank you for sharing!


Very kind and you're quite welcome!
Member Since: October 24, 2012 Posts: 94 Comments: 826
5. NewBerlinTX
4:43 PM GMT on May 28, 2013
Very informative post. Thank you for sharing!
Member Since: August 30, 2011 Posts: 0 Comments: 4
4. 24hourprof
4:27 PM GMT on May 28, 2013
Quoting Thrawst:
Thank you Lee!


You're quite welcome!
Member Since: October 24, 2012 Posts: 94 Comments: 826
3. 24hourprof
4:26 PM GMT on May 28, 2013
Quoting SouthernIllinois:
That was by far one of the most rapid forming tornadoes from a developing supercell that I have ever seen. Furthermore, that tornado underwent one of the most rapid rate of intensification from an EF0 to an EF4 that I have ever seen. If there is such thing as RI (Rapid Intensification) for tornadoes like there is with hurricanes, then this was definitely it!

A truly remarkable and deadly twister. Thanks for the in-depth meteorological look at this event, Lee!


You're quite welcome!
Member Since: October 24, 2012 Posts: 94 Comments: 826
1. Thrawst
4:16 PM GMT on May 28, 2013
Thank you Lee!
Member Since: July 18, 2010 Posts: 50 Comments: 1909

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About 24hourprof

Retired senior lecturer in the Department of Meteorology at Penn State, where he was lead faculty for PSU's online certificate in forecasting.

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