Severe Weather Thread (April 2, 2012 - April 4, 2012)

[tornadotony]

Which of the EF-2 tornadoes was the one tossing the tractor trailer's around? I know it wasnt the EF3 forney tornado... I'm pretty amazed that an EF-2 could lift 10,000 lb+ objects like that and toss them around.

As others noted, the proportion of vertical winds to horizontal winds in the tornadoes seemed unusually high, at least from the videos we have of the event. That, combined with the wide sfc area of the semis that was exposed to the winds, made them easy targets.

[David Reimer]

Considering I was chasing and well in the loop about the behind the scenes events on Tuesday, let me go ahead and brief you on what exactly came into play from a local perspective.

Just after 11 AM CDT, at least 30 minutes before the 1630Z outlook came out with the 10% tornado probability, FWD mentioned an increased tornado risk that afternoon due to an outflow boundary and very high 3 KM CAPE values in NWS Chat. All local media members are in the chat and use it extensively. There was no "surprise" that the tornado potential was going to increase into the early afternoon. Local media members began disseminating that information and began relaying that a Tornado Watch would likely be issued once the mesoscale discussion was put out by SPC. While North Texas has been relatively quiet in terms of major tornadoes during the past few years, the D/FW market has really taken hold of social media. The National Weather Service office in Fort Worth was the first office to have a facebook page and they have close to 15,000 likes. In addition, I put out the word on the Texas Storm Chasers social media platforms (which have over 100,000 followers) that the tornado threat was more elevated then earlier expected and that everyone should have a way to receive weather warnings in the early afternoon hours. The Storm Prediction Center recognized the potential and increased the tornado probabilities and issued a mesoscale discussion highlighting that potential and the likelihood of an upgrade to a tornado watch. We were already experiencing severe weather with the elevated supercells in Hood/Parker/Wise county beginning to become surface based, so all media outlets had their staffing increased. The National Weather Service was no exception and ample man power in place to support warning operations. I headed down to Burleson to intercept the developing supercell that was near Cleburne. While I honestly had not had time to do an in-depth analysis of conditions that morning, I knew that there was a boundary in place over the metroplex and 3 KM CAPE values were in excess of 350 joules per kilogram. That in itself supported a threat for brief spinup tornadoes. I gained a visual of the supercell's base about the time the first report of a tornado came in near Joshua, TX. I had a visual of a wall cloud with some minor rotation, but I was still a good distance away. As the storm began moving closer to my location, it underwent a cycle and looked like it was weakening for about two minutes. I thought the storm was a candidate for a brief tornado at that point. After about two minutes, something occurred which changed my entire perception of the threat. Suddenly and without warning, scud rapidly began rising into the base of the storm. Now mind you, this wasn't my first chase and I've seen plenty of tornadoes. The overall velocity of the rising scud was very fast and wasn't the kind of motion you see on a storm capable of producing "marginal" tornadoes. At that point, I forwarded that information onto FWD, in addition to streaming the entire event with audio. At that same time, a second report came in of a tornado on the ground near a high school in Joshua. I did notice a darker area of contrast to my northwest, but could not confirm visually that a tornado was down. At this point the storm was beginning to move away from my location and began moving north on Interstate 35W. A rotating wall cloud crossed the highway over my location and looked like it was lowering and very well have been in the funnel stage as it crossed just to my north, I'll have to sit down and review the dash-cam video to confirm. Once the circulation passed east of the highway, I moved north to Interstate 20 and blasted east when I began hearing multiple reports of a large tornado on the ground. I ended up just west of Highway 820/US-287 North when I pulled over since I was getting slammed by golfball size hail and was beginning to see a feature to my south. I knew there was a tornado on the ground and that it would pass fairly close to my location, but I was unsure if it was maintaining a more northward movement or had in-fact turned more to the right. I got a frantic call from another chaser about three miles to my house that the tornado was moving at my location and that I needed to go south on Highway 287 to get out of the way, fast. I did just that and had a fairly violent multiple-vortex tornado form about 100 yards to my west as I blasted (by blasted, I mean BLASTED) south on 287. It was in an impressive multiple-vortex stage and was ripping trees of the ground. I got a mile south of the circulation, jumped out of the car and looked north just as the tornado became a large multiple-vortex tornado on Highway 287. This was around the same time that the large tornado was moving through Lancaster, which mind you is pretty close to my house. The rest of the storm's tale is history...

I'll be the first to say I did not expect the significant outbreak we received on Tuesday. I expected a fairly widespread event of very large hail, damaging winds, and maybe a brief tornado. My awareness level went up with that 10% TOR, but I still only called for a "few tornadoes" on the blog. What happened on Tuesday was the perfect storm of boundaries, relative atmospheric conditions, and timing. Do I think anyone "busted" or messed up? Absolutely not! The outflow boundary was a mesoscale feature that could not be resolved by model guidance, even high resolution models. The folks at FWD noticed this boundary at 11 AM and as a result beefed up their awareness level for possible tornadoes. SPC upgraded the severe watch to a tornado watch nearly an hour before the first tornado touched down in Johnson county. All media outlets were already aware of the severe weather potential and had helicopters ready to go, which for the first time, proved to be a major asset with a tornado event in North Texas. As a result of live video and reports, the National Weather Service in Fort Worth was able to confidently increase their warning urgency. ALL local media stations (Television, Radio, and Internet) were on continuous tornado coverage and social media played a major role in providing warning data and relaying reports.

In terms of Texas Storm Chasers, we have multiple individuals that are available to post information on our social media feeds during events. While my business partner Connor and myself were out chasing and not able to post frequent updates, Chelsea Bennett, Jenny Brown, John Burgdorf, and Ryan Sheff (a member of this forum under SmokeEater) were posting constant updates that were shared with tens of thousands of individuals. The reason we do social media is for events like Tuesday, because many people receives updates on their phones and computers. Social media provides an outlet to receive this information almost instantly. While I was viewing a tornado in Kennedale, Texas, those guys were posting the information about where it would be in five minutes.

To those who say that forecasters messed up big time on Tuesday in regards to downplaying (or under-forecasting) the tornado potential, I say go ahead and take a look at model data from the night before and even six hours before the evening. North Texas has to be one of the most prepared regions in the country for a major event. I'm not talking about just Fort Worth and Dallas, but the region as a whole. When we have a major disaster like a tornado outbreak, emergency crews don't operate as a city, but as a region. I arrived in Lancaster, Texas about 90 minutes after the tornado struck and there were emergency crews from cities over 25 miles away. It reminded me of the wildfire events last year. There is a reason no one died on Tuesday. Sure, some luck plays into it, but with so many populated areas being hit by strong tornadoes within such a concentrated zone, it's amazing that no one was killed. Weather education plays a big role here in North Texas. Complacency due to the lack of tornadoes over the past ten years may have been an issue before in D/FW, that complacency was shot to hell on Tuesday. Anyone who says the weather service did a bad job obviously doesn't know what they're talking about because FWD performed amazingly. Warning lead-times, warning urgency, severe weather reports, and the overall use of social media during and after the event shows why FWD is one of the best WFOs in the United States.

[Minnesota Meso]

Considering I was chasing and well in the loop about the behind the scenes events on Tuesday, let me go ahead and brief you on what exactly came into play from a local perspective.

Just after 11 AM CDT, at least 30 minutes before the 1630Z outlook came out with the 10% tornado probability, FWD mentioned an increased tornado risk that afternoon due to an outflow boundary and very high 3 KM CAPE values in NWS Chat. All local media members are in the chat and use it extensively. There was no "surprise" that the tornado potential was going to increase into the early afternoon. Local media members began disseminating that information and began relaying that a Tornado Watch would likely be issued once the mesoscale discussion was put out by SPC. While North Texas has been relatively quiet in terms of major tornadoes during the past few years, the D/FW market has really taken hold of social media. The National Weather Service office in Fort Worth was the first office to have a facebook page and they have close to 15,000 likes. In addition, I put out the word on the Texas Storm Chasers social media platforms (which have over 100,000 followers) that the tornado threat was more elevated then earlier expected and that everyone should have a way to receive weather warnings in the early afternoon hours. The Storm Prediction Center recognized the potential and increased the tornado probabilities and issued a mesoscale discussion highlighting that potential and the likelihood of an upgrade to a tornado watch. We were already experiencing severe weather with the elevated supercells in Hood/Parker/Wise county beginning to become surface based, so all media outlets had their staffing increased. The National Weather Service was no exception and ample man power in place to support warning operations. I headed down to Burleson to intercept the developing supercell that was near Cleburne. While I honestly had not had time to do an in-depth analysis of conditions that morning, I knew that there was a boundary in place over the metroplex and 3 KM CAPE values were in excess of 350 joules per kilogram. That in itself supported a threat for brief spinup tornadoes. I gained a visual of the supercell's base about the time the first report of a tornado came in near Joshua, TX. I had a visual of a wall cloud with some minor rotation, but I was still a good distance away. As the storm began moving closer to my location, it underwent a cycle and looked like it was weakening for about two minutes. I thought the storm was a candidate for a brief tornado at that point. After about two minutes, something occurred which changed my entire perception of the threat. Suddenly and without warning, scud rapidly began rising into the base of the storm. Now mind you, this wasn't my first chase and I've seen plenty of tornadoes. The overall velocity of the rising scud was very fast and wasn't the kind of motion you see on a storm capable of producing "marginal" tornadoes. At that point, I forwarded that information onto FWD, in addition to streaming the entire event with audio. At that same time, a second report came in of a tornado on the ground near a high school in Joshua. I did notice a darker area of contrast to my northwest, but could not confirm visually that a tornado was down. At this point the storm was beginning to move away from my location and began moving north on Interstate 35W. A rotating wall cloud crossed the highway over my location and looked like it was lowering and very well have been in the funnel stage as it crossed just to my north, I'll have to sit down and review the dash-cam video to confirm. Once the circulation passed east of the highway, I moved north to Interstate 20 and blasted east when I began hearing multiple reports of a large tornado on the ground. I ended up just west of Highway 820/US-287 North when I pulled over since I was getting slammed by golfball size hail and was beginning to see a feature to my south. I knew there was a tornado on the ground and that it would pass fairly close to my location, but I was unsure if it was maintaining a more northward movement or had in-fact turned more to the right. I got a frantic call from another chaser about three miles to my house that the tornado was moving at my location and that I needed to go south on Highway 287 to get out of the way, fast. I did just that and had a fairly violent multiple-vortex tornado form about 100 yards to my west as I blasted (by blasted, I mean BLASTED) south on 287. It was in an impressive multiple-vortex stage and was ripping trees of the ground. I got a mile south of the circulation, jumped out of the car and looked north just as the tornado became a large multiple-vortex tornado on Highway 287. This was around the same time that the large tornado was moving through Lancaster, which mind you is pretty close to my house. The rest of the storm's tale is history...

I'll be the first to say I did not expect the significant outbreak we received on Tuesday. I expected a fairly widespread event of very large hail, damaging winds, and maybe a brief tornado. My awareness level went up with that 10% TOR, but I still only called for a "few tornadoes" on the blog. What happened on Tuesday was the perfect storm of boundaries, relative atmospheric conditions, and timing. Do I think anyone "busted" or messed up? Absolutely not! The outflow boundary was a mesoscale feature that could not be resolved by model guidance, even high resolution models. The folks at FWD noticed this boundary at 11 AM and as a result beefed up their awareness level for possible tornadoes. SPC upgraded the severe watch to a tornado watch nearly an hour before the first tornado touched down in Johnson county. All media outlets were already aware of the severe weather potential and had helicopters ready to go, which for the first time, proved to be a major asset with a tornado event in North Texas. As a result of live video and reports, the National Weather Service in Fort Worth was able to confidently increase their warning urgency. ALL local media stations (Television, Radio, and Internet) were on continuous tornado coverage and social media played a major role in providing warning data and relaying reports.

In terms of Texas Storm Chasers, we have multiple individuals that are available to post information on our social media feeds during events. While my business partner Connor and myself were out chasing and not able to post frequent updates, Chelsea Bennett, Jenny Brown, John Burgdorf, and Ryan Sheff (a member of this forum under SmokeEater) were posting constant updates that were shared with tens of thousands of individuals. The reason we do social media is for events like Tuesday, because many people receives updates on their phones and computers. Social media provides an outlet to receive this information almost instantly. While I was viewing a tornado in Kennedale, Texas, those guys were posting the information about where it would be in five minutes.

To those who say that forecasters messed up big time on Tuesday in regards to downplaying (or under-forecasting) the tornado potential, I say go ahead and take a look at model data from the night before and even six hours before the evening. North Texas has to be one of the most prepared regions in the country for a major event. I'm not talking about just Fort Worth and Dallas, but the region as a whole. When we have a major disaster like a tornado outbreak, emergency crews don't operate as a city, but as a region. I arrived in Lancaster, Texas about 90 minutes after the tornado struck and there were emergency crews from cities over 25 miles away. It reminded me of the wildfire events last year. There is a reason no one died on Tuesday. Sure, some luck plays into it, but with so many populated areas being hit by strong tornadoes within such a concentrated zone, it's amazing that no one was killed. Weather education plays a big role here in North Texas. Complacency due to the lack of tornadoes over the past ten years may have been an issue before in D/FW, that complacency was shot to hell on Tuesday. Anyone who says the weather service did a bad job obviously doesn't know what they're talking about because FWD performed amazingly. Warning lead-times, warning urgency, severe weather reports, and the overall use of social media during and after the event shows why FWD is one of the best WFOs in the United States.

David: thank you for this post, I think this puts things into the proper prospective, while many people will argue (and have) as to whether this outbreak was historical or just a common occurrence in this part of the country, based on climatology is absolutely ridiculous IMO. If this isn't a significant historical event, it will be at least referred to as a significant event, if that make any sense.

Now that I said that. I expect one of two things will transpire over the Northern Plains to Upper Mississippi Valley later this year, especially in Minnesota. The drought will get worse or we will see something akin to 2010, I don't think there will be anything in between. If severe sets up like it may (the key word here is may) and we see some moderate risk up here I hope you have the time and resources to chase up here. The area west of line from RST to MSP is prime chase area. The terrain is fairly flat, you can see for miles, and the road network is the best in country IMO.

Good luck for the rest of the season!!!

[radarman]

Considering I was chasing and well in the loop about the behind the scenes events on Tuesday, let me go ahead and brief you on what exactly came into play from a local perspective

Cool account. Sounds like you had a close call... I'm glad you guys have each others backs out there and the communication was solid.

You report multi-vortexes and I've seen that referred to in other places too. I wonder if that doesn't contribute to the apparently muddled velocity signatures in the radar data. I've seen as much as 35 kts of spectral width in the tornadoes, which is certainly very high, but I don't know off-hand how that compares with other strong, single vortex tornadoes.

--edit

The 35 kts of W are actually in the low reflectivity areas out ahead of the storm. Near the vortices, the max W's are more like 15-25 kts.

[AtticaFanatica]

You report multi-vortexes and I've seen that referred to in other places too. I wonder if that doesn't contribute to the apparently muddled velocity signatures in the radar data. I've seen as much as 35 kts of spectral width in the tornadoes, which is certainly very high, but I don't know off-hand how that compares with other strong, single vortex tornadoes.

Depends on the spatial resolution. For example, check out Wurman (2002), where the multiple vortices are spatially resolved (you can see the signatures in DZ,VR, and SW). That was a mobile radar and a huge tornado, so that's usually not going to be the case, but you can certainly see how they might affect the signatures if they were stuck inside a resolution volume.

http://journals.ametsoc.org/doi/full/10.1175/1520-0434%282002%29017%3C0473%3ATMVSOA%3E2.0.CO%3B2?

[radarman]

Depends on the spatial resolution. For example, check out Wurman (2002), where the multiple vortices are spatially resolved (you can see the signatures in DZ,VR, and SW). That was a mobile radar and a huge tornado, so that's usually not going to be the case, but you can certainly see how they might affect the signatures if they were stuck inside a resolution volume.

http://journals.amet...A%3E2.0.CO%3B2?

Thanks for the link. Really cool to see the individual vortexes at that resolution. (no scale though bizarrely)

It's true of course that the greater percentage of the vortex contained in a single resolute volume, the higher you'd expect the spectral width, and the size of that volume is a function of beamwidth and distance. A weak EF0 spinup vortex might well fit entirely in one gate and be characterized by high W and near zero measured velocity. Looking at a single flank of a large tornado would likely have comparatively lower W, although there's enough chaotic motion within that it's still probably higher than most thunderstorm winds.

In this case the Arlington tornado was between 4-8 miles away from the radar at it's peak... The couplet is evident over many beamwidths at that distance and the spectral width is high anyway. (actually much higher on the inbound side that the outbound side for some reason)

But as you can see the couplet here is fairly clean and well defined, and doesn't have the "muddled" look as I mentioned that was more with the Lancaster, and especially the Forney tornadoes.

Obviously much further away with larger gate widths you might expect the Forney tornado to have higher W's. Comparing the two at the same height AGL they're pretty similar on the whole. Unlike the data in the Wurman paper which is very clear, drawing any conclusions from the Nexrad W seems to be difficult at best. But still think it's not impossible that multi-vortices may have contributed at least somewhat to apparently lower tangential velocities in the averaged moment data than the damage might suggest.