News DetailAnalysis of Greensburg, KS tornado environment
Posted At: May 13, 2007 @ 11:40 PM
Posted By: Reed Timmer
Related Categories: Tornadoes
Here is a brief model/observational analysis of the Greensburg, KS tornado environment by John Davies, who produces exceptional reports for nearly all significant tornado events. As expected, the instability/shear indices matched the analogue violent tornado cases very closely, but with higher instability.
http://members.cox.net/jondavies6/050407greensburg/050407greensburg.htm
An issue I have with this study is the time focus of the shear/instability analysis. The shear/CAPE plots for only 00z (7pm CDT) were discussed (except for the two erroneous RUC analysis plots from later in the evening), and used for comparison with historical violent tornado cases. However, the rapid intensification of the low-level jet after 00z likely played a substantial role in the development of violent tornadoes with this storm. The WRF forecast the large 0-1 km helicity values to be confined to the warm front in central KS at 00z (as displayed in John Davies' report), however, substantial low-level shear was also likely present to the south of the warm front and east of the dryline extending into northwest OK after 00z as the nocturnal low-level jet intensified. In my opinion, the role of the nocturnal low-level jet in producing the first EF-5 tornado did not receive enough attention in this analysis.
http://members.cox.net/jondavies6/050407greensburg/050407greensburg.htm
An issue I have with this study is the time focus of the shear/instability analysis. The shear/CAPE plots for only 00z (7pm CDT) were discussed (except for the two erroneous RUC analysis plots from later in the evening), and used for comparison with historical violent tornado cases. However, the rapid intensification of the low-level jet after 00z likely played a substantial role in the development of violent tornadoes with this storm. The WRF forecast the large 0-1 km helicity values to be confined to the warm front in central KS at 00z (as displayed in John Davies' report), however, substantial low-level shear was also likely present to the south of the warm front and east of the dryline extending into northwest OK after 00z as the nocturnal low-level jet intensified. In my opinion, the role of the nocturnal low-level jet in producing the first EF-5 tornado did not receive enough attention in this analysis.
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With the number of large tornado forming towards sundown or later this year, it is hard to argue against the low level jet playing a major role in the formation of big tornadoes afterdark. Feb 28, the tornadoes only got bigger as it got later in the evening, way bigger. March 28th, they were a pretty good size before dark, but were incredible after dark. Then of course there is May 4th, we all know what happened there.
tragic story
Here is the latest on the Greensburg Tornado. It contains a Level 2 radar velocity image showing 200+ mph gate-to-gate shear. It also has the tornado paths. VERY IMPRESSIVE!!
http://www.crh.noaa.gov/crnews/display_story.php?wfo=ddc&storyid=7828&source=0
That's an amazing radar image...I wonder if the tornado actually made a loop as shown in the track map. I don't think I've ever seen a tornado do that. They always seem to turn left while occluding but not make a complete loop. crazy.
Reed, I came across your website a few days ago, and want to compliment you highly on it, and on everything you do. I viewed all your stock footage videos and they are just astounding. How in the world do you figure out exactly where to be when a tornado forms, is that something you've ever discussed on this site? Anyway, kudos from a very wowwed surfer. Thanks again and keep up the good work.
John Davies continually refers to the backing of the surface winds and their resultant increase in SRH. However, while backing surface winds are important, it is equally important to note the increase magnitude in the low-level jet (LLJ). Horizontal vorticity strengthened as the LLJ cranked up to near 50ktsn (and the tilting and stretching of this vorticity aided in strong rotating updrafts). While the backing of the winds aided in the increase SRH, Reed hits it dead on that the strenthening nocturnal LLJ was more likely responsible for the favorable environment. The LLJ typically peaks around 2 am, thus the storms continued to produce tornadoes well into the overnight hours on 4 May 2007. One point Davies hits on is the importance of the storms being surfaced based. SRH frequently increase in the evening as the LLJ intensifies, but if the environment is capped or if the storms are elevated then you won't likely see tornadoes. The approaching storm systems likely advected cooler temps aloft to enhance the amount of 0-3 km CAPE.
Wes, one reason why you might see larger tornadoes near and after sunset is because the LCL heights tend to come down as the dewpoint depression decreases. Typically, as stroms form in the afternoon, the air mass in the boundary layer is fairly mixed. Thus, storms tend to have a higher base at first and eventually work their way closer to the surface. At sunset, the temps are already cooling since the outgoing longwave (LW) radiation is much greater than the incoming shortwave (SW) radiation. This combined with the advection of moist air (higher dewpoints) allows in the lowering of LCL heights.
This is just one possible reason. Reed is much smarter than me so he will likely have more info on the subject.
When I said size, I was referring more to an increase in wind speed than physical size. The tornadoes I have seen have been wider at night, but I was talking more about how the ones after dark have also been getting higher ratings. I am sure the drop in LCL's after dark and the increasing LLJ both have had their hand in the creation of some of the nighttime tornadoes I have seen this year.
ya didn't have to be mean about it chirs.
I see... not the actual width of the tornado, but the strength as determined by the damage. I have not looked into the EF-scale ratings given in the several tornado outbreaks so far this year. I am familiar only with a couple 4 May, 28 March, and 5 May. I do agree that the strengthening LLJ plays a huge role in the development of strong rotating updrafts and tornadoes.
Here are a couple of other things to possibly consider.
Throughout most of the tornado events this year the CAP has been relatively strong during the afternoon limiting development till late in the evening. This inhibition of convection during the afternoon allows for a couple of things. First, prolonged day time heating will enhance the convective available potential energy. Higher CAPE values will yield the potential for stronger vertical velocities (Wmax=[2*CAPE]^.5), thus the updraft will be stronger. Second, the longer it takes for storms to form the closer it will be to sunset. So far this year we have had these parameters and strong storm systems to thank for increased intensity, as determined by the damage rating. The combination of very HIGH CAPE, due to strong CINH and temp/moisture advection throughout the afternoon hours, as well as the strengthening of the LLJ near and after dark led to the increased frequency of stronger tornadoes at night.
There are several equations which relate available energy and shear (EHI and BRN).
I hope this might help explain why there have been stronger tornadoes near and after sunset so far this year.
Hey Reed whats up, there is a slight risk for St.Louis tomorrow what do you think? Great video of the F5 watched it a ton have a nice day.
Oh and one more thing what time of day do u think it will start Thank you again Have a nice day.
j-man I think it will start in the afternoon because
heating of the day is the fuel for thunderstorms.
oh and I'me not trying to scare you but some
day thre will be a supertornado in your downtown area
plese post me back so we can chat about this.
and are you new here?
Ya im here ya i saw that on TWC lol it would be nuts alot of people downtown they say safest place would be the under the arch i herd it will be in the morning for the storms lol idk
umm... hmmm.... what dose lol and idk stand for
ha ha I know that is a dumb question j-man.
laugh out loud and i dont know
ya i dont think that will happen anytime soon tho when it does it will be crazy alot of people downtown i would rather see the Tornados in the fields alot of fields around me
j-man It will happen anytime. IT WILL HAPPEN SOON
You dont know that lol
im in downtown all the time shh
This tornado was extremely strong, but i know sometime before the year 2050, someones gonna get the big one (EF5) come through, im from Indiana, and the last major tornado in the area im from was on June 2, 1990 when an F4 toar through Petersburg, Indiana. The last F5 that hit Indiana happened on April 3, 1974 during the super outbreak of 148 tornadoes.