The 4 year Anniversary of the Historic Carolina Tornado Outbreak 4/16/2011


I wrote this blog a few days after the historic tornado outbreak in North Carolina on April 16th, 2011. This ended up being the largest tornado outbreak in state history. 30 confirmed tornadoes occurred in North Carolina on 16 April 2011, the greatest one-day total for North Carolina on record.

A total of 24 individuals lost their lives in North Carolina with thirteen tornadoes classified as strong, some hitting highly-populated areas.

My preliminary findings are that some of the same ingredients that spawned the March 28th, 1984 outbreak were also present in this one. From a synoptic standpoint they were similar but not exact. This time around though 4 key factors have come to my attention and I believe they caused so many significant and long track tornadoes this time around. First though here’s some of the imagery and tracks of the tornadoes I have accumulated so far as of this writing on 4/19/11. This was a huge 3 day outbreak across the entire U.S.

( Image Credit Victor Gensini at UGA.)


Lots of images are mine with some from WRAL-TV, which did outstanding coverage not only because of their knowledgeable meteorologists but their technology. They are lucky to have a radar based in Fayetteville which gave them great views of the storms. They also have one of the first Dual-Pol Doppler radars in the country. Even though it was a great resource these storms were so text book and intense that all the radars detected debris with the long track tornadoes. Below are the tracks of the supercells estimated from the Doppler radar shear(WRAL) and rainfall estimates on the left. The images on the right show the number of warnings issued and the current storm reports.



The radar images were just incredible, most showed well defined hook echoes which in and of themselves are indicative of a tornado. What was even more amazing was the presence of debris balls on the radar imagery. These are basically the Doppler radar detecting debris, i.e… parts of homes, businesses, cars and trees airborne due to the tornado.



To me this picture says it all with the radar & Skycam from WRAL-TV showing the tornado bearing down on Raleigh.


I have all my images saved on my Twitpic account and you can view them by clicking  here.

What made these storms so intense? Here are some of the factors I believe contributed to the significant and long track tornadoes.

#1 Very low LCL’s (Lifted Condensation Levels) were present. The storms bases were extremely low meaning the mesoyclones were very close to the ground and made for easy tornado genesis. You can see this from the videos and pictures notice how short and stocky these tornado were. Low LCL’s are known to allow easy formation of tornadoes simple because the distance between the cloud base and ground becomes so small. When the wall cloud forms it shortens the distance further meaning the tornado has a much easier time forming. This has to do with the relationship between the RFD(Rear Flank Downdraft) and the inflow into the storm. Low LCL’s have shown a 64% correlation to significant tornadoes. (source Warning Decision Training Branch (WDTB) Tornado Warning Guidance: Spring 2002)

Below you can see the the NAM forecast on the left and the special 16z sounding from GSO. The WDTB research showed that the median LCL for significant tornadoes was 780m, the sounding from GSO had a LCL of 262m at 16z.


More evidence of the low LCL can be seen from video and pictures. Notice how all the images show a very short and relatively wide vortex. The distance from the clouds base to the ground was extremely small, meaning that the mesocyclone was almost all the way down to the ground.

low lcl



#2 Gravity waves, these were present on the satellite imagery during the morning over North Carolina and South Carolina. Not only that I noticed them as well near where the Tushka,OK tornado formed on Thursday 4/14/11 and near the Clinton, MS tornado on 4/15/11. Here’s a look at the gravity waves on the satellite imagery from the 3 day outbreak.

Tushka,Oklahoma                                     Clinton, Mississippi


North & South Carolina


Why are these gravity waves important? Meteorologist Dr. Tim Coleman from the University of Alabama at Huntsville found that they compress the storms causing them to spin faster due to conservation of angular momentum. Think figure skater pulling their arms in and spinning faster. Or playing tether ball as the rope gets smaller the ball spins faster around the pole. Coleman also notes, “There is also wind shear in a gravity wave, and the storm can take that wind shear and tilt it and make even more spin. All of these factors may increase storm rotation, making it more powerful and more likely to produce a tornado.” Dr. Coleman has a model that shows how a gravity wave interacts with a tornado. Notice the increase in vorticity as the gravity wave interacts with the storm. (credit [email protected])


#3 Wind shear, this was obvious, we had some epic wind shear with this event. The storm relative helicity from the special 16z GSO sounding was 611 m2/s2 at the SFC-1km and the SFC-3km SRH was 702 ms/s2. The STP ( Significant tornado parameter) was off the charts for this reason. STP on the left Skew-T on the right.


#4 The echo tops were key as well. Clearly once these storms hit about 40,000’-50,000’ in height they were able to fully tap into all the shear that was present within the entire column of the lower atmosphere. Part of the reason this happened was due to the heating and the CAPE increasing as clearing was occurring ahead of the front. This CAPE or surface based instability then in turn caused the updrafts to become well established and grow in height. Notice how storm tops changed dramatically from around noon time over the I-77 corridor near Charlotte to around 3pm east towards Raleigh and Fayetteville. Scale is on the left side of the image below.

Storm Tops near Raleigh                                       Storm Tops near Charlotte

tops easttops west

Still working on putting stuff together and all of this is just preliminary. This outbreak will go down as one of the biggest in the SE and Carolinas all time. It’s always hard to compare modern outbreaks to older outbreaks due to population density, technology and changes in documentation. I have a few maps via Google Earth I’m working on and will keep studying this event and be on the look out for further posts on the subject. I’d love your feedback and discussion on the topic in the comments section below.  Still a work in progress…. bear with me it’s been a long 2 weeks in the Carolinas.

Google Earth Virtual Tour of Sanford-Raleigh tornado track. 20110418071005-4dac463d666f19.08853572.kmz

tornado tracks so fartracks


  • Brad –

    It is amazing how much news as changed in such a short period of time. The radar and mobile technology now available makes telling the whole story of a widespread news event like this from multiple perspectives possible. It is awesome how you’ve combined radar & science with pictures and videos to explain the outbreak of tornadoes. While all of this is readily available, it takes a lot of work to compile it into such a great post. That’s why you are at the front of the pack. Awesome work!

  • wxbrad

    thanks Rich, yeah took a while and I could write 4 more posts just on all this stuff. Hope we never see this again around here.

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  • Hi Brad,
    I was wondering if you could tell me if the town of Fuquay Varina around the zip 17526 was hit hard by any of the tornadoes? I have family and we have not been able to reach anyone since the storms rolled through.

  • Hi Brad-

    Awesome write-up and compilation of the pertinent material. I really enjoyed reading this. It’s a sad event from the view of all the personal and material loss that many families went through, but it was a pretty exciting event from a solely weather-based view.

    We had pretty ho-hum weather on the western side of the state with this system. All the bells and whistles occurred to our east. I suppose topology has a lot to do with this as well as time of day for the frontal passage (late afternoon with peak heating versus early morning). Anyway, it’s an event for the record books.

    • I think it was luck. There’s less tornado frequency in western NC (I lived in Boone for 12 years, by the way). But I think it has more to do with the way that the worst of these storms often bring their energy into the state from the southwest.

      April 1-4, 1974: two separate outbreaks spawned a total of 5 tornadoes in Cherokee County, including 1 F4. The storms on April 3-4 were connected to the Super Outbreak, which did produce a number of tornadoes over very rugged terrain in GA, NC, and especially WV.

      There was an extremely violent outbreak that crossed West Virginia in 1944 as well. The May 31, 1985 outbreak in Pennsylvania, which produced an F5, along with an F4 that was well over 2 miles wide at one point, began over flat ground in eastern Ohio, but rolled up and over the ridges of the Alleghenies in central PA like it was nothing.

      And there is the infamous Yellowstone tornado in 1987. This was an F4, one mile wide, which didn’t hit any structures (it was in a roadless wilderness area), but it crossed the continental divide at just under 11,000 feet above sea level. Ted Fujita wrote a rather lengthy paper on this storm, and tornado climatology in mountainous areas in general – much of his work and ideas came from a few campers who observed that tornado from a few miles away, and noted it’s intense fluctuations in intensity as it moved up, or down a ridge – at ridgetops the mesolow was pretty much on the ground, and the damage path would become very wide and very intense, weakening on the down slope of a ridge, and strengthening on the up slopes… That storm pulverized hundreds of acres of timber.

  • Hey Brad,

    Excellent post! As Rich said, you’re out in front of everyone with electronic/social media. You are a trendsetter in our field. It’s clear you love this stuff and enjoy putting in the hard work to create posts like this (believe me; I know it’s a lot of work). Anyway, I always enjoy seeing what you are going to come up with next. This was a lot of fun to read. Hope we get the chance to hang out at a weather conference again in the near future! It is fun talking shop with you. Oh and how you find the time for this stuff with your little guy at home now is beyond me. 😉

  • wxbrad

    Thank you to everyone for the feedback, it’s overwhelming how this post has spread so fast. Guess I’m not the only weather geek out there. I’m still working on the case study for possible presentation at NWAS11 & The American Weather Conference. So if you have any archived synoptic charts, upper air, radar or satellite data that might be of use please share it if you can. You can e-mail me at [email protected].

  • wow that thing was huge on the Raleigh picture and brad thanks for the hard work it makes telling my friends the weather a lot easier

  • ctb

    This event isn’t quite as impressive to me as some are making it out. Certainly by Carolina standards it was epic. Certainly a huge tornado outbreak overall with deaths in OK, AR, MS, AL, and NC.

    There are certainly comparable outbreaks. I mean, even recently in the southeast. April 24, 2010 had the huge EF4 across MS for well over a hundred miles and 2 EF3 tracks across AL similar to the NC tracks. The AL ones just happened to not strike heavy population centers and kill people.

    Obviously Super Tuesday takes the cake in southeast outbreaks since 2000. 4 EF4s, 57 deaths, and 87 tornadoes in 15 hours!!!

    This was a huge outbreak, but with no EF4s I have trouble calling it particularly intense because of the lack of EF4s and the long duration.

  • Brad, this is outstanding! Thanks so much for all the time and effort you put into this! I followed you on Twitter & FB and watched the radar all day, alarmed at what I was seeing, especially after the storms moved out of here (SE York Co). The storms intensified and looked wicked just East of us and all the way up thru Eastern NC. Unbelievable that those 60+ mile tornadoes occurred. Boggles the mind. I hope and pray we never see a recurrence or anything even close to this event!

  • cool. i hope there are no more

  • Brad, those are not gravity waves in the satellite images. In the Oklahoma case those are oragraphically-forced standing waves in the stable morning boundary layer. In the other two cases, they are horizontal convective rolls (sometimes called cloud streets).

    • wxbrad

      Thanks Kevin, you might be correct on the Oklahoma case might have to get more satellite images to confirm. I think it’s hard to tell whether is a standing wave or oragraphically induced gravity wave. The other two I’m little more confident in due to there location & orientation. I would expect to see cloud streets further south in the warm/moist advection coming in from the Gulf or Atlantic. In the Carolina case these waves were not parallel to the low level flow which was SE. I’ll try to track some more images down and some more soundings further south to see if there were convective rolls present. Love some input from others on what they might be as well.

  • Great information! I’ve been looking for something like this for a while now. Thanks!

  • nice post. thanks.

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  • i was within 150 yards from the EF-3 witch tracked through southen greene co. in n.c. and have tracked the entire path. It was an amazing event.I also have damage photo’s that i took the day after, that i would like to email you. I also lived 3 miles from the F4 tornado which came thru in March of 1984, apon further study the 2 systems were very similar in nature when comparing there dynamics.From a non scientific perspective I think a couple of events prevented the tornado’s in april from growing into EF-4, it was cloudy all day with only a few breaks in the day which hampered the heating,and maybe you can enlighten me abit but it was very windy all day with SE winds sustained near 20, in 1984 it was clear all day with little wind, but those came thru at night.One more question I have generally in eastern N.C. we have a sea breeze which blows inland makeing somthing like a dry line, do you think that any effect in the way the storm blew up.
    Excellent post!

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  • Tom Link

    Thanks for a great post. You’ve captured the radar in Raleigh, just as the tornado was trashing my home (3:46, pic 8)