El Reno's Monster, Oklahoma, 5/31/2013 - John

Many of you have probably read my blog post concerning the tragic events that befell the members of TWISTEX, and my thoughts about the environment and the chasing approach that we should take (if not see here: In Our Memories - Passing of time, Paul and Carl). I would like to share with you now the exact events of our chasing experience, and how the tornado event unfolded from our viewpoint (Click on any photo to see a larger version of the shot, especially panoramics).

We began the day in south Oklahoma city (OKC) - in a hotel we would rather forget. The morning was overcast with stratocumulus that was beginning to break under heating by the late morning. A quick look at the forecast for the boundary/trailing front and dryline intersection suggested that the optimal location for the backing of the winds to the southeast and reasonably long hodographs would be somewhere between El Reno and Chickasha, while strong thermodynamics and moderate shear would yield a quite a potent environment. Dynamic models suggested a scenario with several large supercells forming west of OKC in the late afternoon when the environment was primed; what appeared a classic scenario for a regional tornado outbreak. The SPC chose to go with a 15% hatched tornado probability for the area, and a moderate risk, unsure of how widespread the event might be. My choice of an initial target was El Reno - my preferred spot for central Oklahoma dry-lines, with good options north, south and west. I've been burnt before by not waiting for the late initiation in this area, particularly southwest of OKC, and felt this was a good opportunity to turn that around.

As things evolved, the environment became progressively more unstable - with surface observations pushing temperatures of 90F and moisture as high as 77F. The dryline (a moisture gradient) began to surge eastward in response to diurnal heating and the surface cyclone further north, with temperatures exceeding 103F and dew-point temperatures below 40F to the west of the dryline. The environment remained highly capped all afternoon, with towers bubbling against the warm layer of the inversion over the warm sector. A particularly dangerous situation tornado watch (issued to reflect high probabilities of significant tornadoes and thus greater risk to population) was issued at approximately 21:00Z (4pm local), with a 90% probability of two or more tornadoes in the watch area, and a 70% probability of 1 or more significant tornadoes. The risk was also mentioned for hail to 4 inches (though a quick look at the forecast 5000 J/kg CAPE was ringing alarm bells anyway) - so it looked like the core of any storm was going to be a seriously risky prospect.

We met up with Brad, Marko and Valentina at a certain petrol station in El Reno (which seems to be the center of the world), and Rose suggested it would be far nicer to wait out at the lake on the west of town - how right she was. At the lake we ran into Skip Talbot, Nick Nolte, Tony Laubach, Jennifer Brindley and a few others, and enjoyed watching the locals splashing about as the convection bubbled in the oppressive heat. Sure enough, a couple of weak towers made it through shortly after 21Z (4pm), and began to develop into a line of strong storms to our west. Initially, I was concerned by the relative proximity of the three cells, but surprisingly they seemed to suffer little ill effect, probably because of the adequate shear in the 0-3 kilometer layer. We hit the road on our own at around 4:50pm, and decided to drop south out of El Reno and west towards the southernmost storm which was beginning to mature. Yet another cell initiated on its southern flank, but again, the shear and strength of the main cell dominated and simply absorbed it - it looked like we had our storm. We approached into a nice position to the east, and ran into a few Australians on a hill shooting the incredible lightning bolts coming from the cells anvil. At 5:30 (see below) we positioned just north of an east road to watch the cell mature and try to shoot some of the incredible CGs - unfortunately, handheld daytime shots only yielded partial frames, but the GoPro really enjoyed the view (video to come)!

'Winding Up' - The supercell west of El Reno begins to take shape, with the development of structure while producing large positive lightning strikes. El Reno, OK, 31/5/2013

The cell began to get serious about inflow and I decided to move us back further east to avoid any issues while it wasn't looking the best. The next view we got in a driveway began to show the storms structure properly as the inflow howled - I could barely stand, and holding the camera steady was incredibly difficult.

'Rapid Development' - The supercell takes a classical, though slightly high precipitation morphology, with an impressive barrelled structure and inflow that made it hard to stand. Near  El Reno, OK, 5/31/2013.

The structure of the storm at this stage was also a sight to behold and probably the highlight, as it began to really spin up to drop a tornado:

Oklahoma Scissor-tail- Like the state bird of Oklahoma, scissor-tailed inflow stretches into the strengthening mesocyclone as a tornado begins to develop. Near El Reno, OK, 5/31/2013.

'Sculpted Above and Below' - The tornado begins to develop, with an inflow tail visible under the incredibly sculpted barrel mesocyclone. Near El Reno, OK, 5/31/2013.

'Fields of Gold' - The clouds contort as the supercell focuses its energy to the central circulation, as vortices begin to periodically extend from the ground to cloud. El Reno, OK, 5/31/2013

By 6:03 we were in position on a north-south road (see map below) as the tornado touched down from the awesomely structured mesocyclone - Rose's first real tornado, which made things a bit exciting. I can't say I was having the best day and found myself somewhat disorganised as the tornado oscillated between different strong subvortices.

GPS log file for our chase, plotted by the red path, while overlaid in light blue is the damage path of the El Reno EF-5 tornado. Note that times correspond to GPS position and thus should be relatively exact. Our closest approach to the tornado was likely when were about to cross US81 where I estimate it was within 1 mile of our position directly to the west.

Even though I was disorganized, the photos really captured the moment of the storms peak organisation:

'Multivortex Majesty' - The tornado touches down with multiple vortex tendrils extending from the supercells base and a strong inflow tail.

'Layered Twins' - The spectrum of colour stretches from bottom to top with twin vortices, from the verdant fields and into the clouds. El Reno, OK, 5/31/2013

'Below the Mesocyclone' - The stovepipe tornado stretches down below the structure of the supercell mesocyclone  and tornado cyclone southwest of El Reno, OK. Note the incredible tail cloud at the bottom right. This would go on to become the EF-5 2.6 mile wide monster. 5/31/2013

'The Beast Retreats' - The tornado darkens and grows in size, though little would suggest that soon this monster would stretch to over two miles. El Reno, OK, 5/31/2013.

'Under the Meso' - As the mesocyclone approaches, the dark tornado and rapid rotation stretch to our west. The time to run from the storm is at hand. El Reno, OK, 5/31/2013

The wind again began to howl over us, and seeing that the tornado was approaching rather quickly, I elected to race us east to avoid the hordes of chasers getting out of the way. When we crossed Route 81 behind Skip and Nolte at 6:16, images I have seen shown the tornado perhaps a mile to our west, more than close enough for my mind! We shot further east, and pulled up at the point labelled 6:26, when the structure of the storm was exposed beautifully with the now giant wedge tornado (2.6 miles diameter of radar derived EF-1 winds) buried underneath - incredible and yet frightening given the position of certain chasers on spotter network.

'Benath the Beast' - A large EF-5 Wedge tornado near El Reno, Oklahoma. The tornado had the distinction of being the widest recorded, with EF1 winds to a diameter of 2.6 miles. Sadly, the storm took 4 storm chasers lives. Southeast of El Reno, 5/31/2013.

'The El Reno Wedge' - A large EF-5 wedge tornado under an enormous HP/Classic supercell observed from southeast of El Reno/Union City, 5/31/2013.

Given that a new mesocyclone appeared to be forming on radar to our northwest, and was moving southeast toward us, my concern was that we could be in the path of a second tornado. This concern was deepened by hearing tornado warnings issued for our position, but poor visibility and the more urbanized environment meant that the situation was becoming unsafe, so we decided to get out of the line of fire. To do so, we continued to drop south and east to avoid the old RFD (rear flank downdraft) surge and the new mesocyclone.  However, as we approached the outskirts of the metro we were slowed by traffic, leading to a relatively close call (see the map below) to the south/southwest of the second tornado that went on to impact the airport and southern OKC. A poor decision that went against the wishes of my navigator (who wanted to take Route 4 as the river crossing instead of Interstate 44) probably exposed us to more of the panicked exodus from OKC than we desired, but still, we made our escape without a scratch and stayed the night in Chickasha, OK. The full path of our chase relative to the two tornadoes can be seen below.

Full chase log for the 31st of May west of Oklahoma City. Chase began at 4:50pm and continued through 8pm. The two light blue areas correspond to the (left) El Reno EF-5 which occurred between 6:03 and 6:43, and the (right) Airport/South OKC EF-1 that began at 6:51 and continued through 7:23pm. Note the closest approach to the second tornado path was at 6:50, and the tornado quickly became rain-wrapped, which is when the decision was made to turn south.

Looking back on the day, there are a few things I would have perhaps done slightly differently. The first relates to being prepared with the video camera gear - or at least remembering that the D800 has a video setting. I had a great opportunity to record the tornado and at the same time shoot photos - but instead wasted time stuffing around with a video tripod mount. Not my proudest moment right there, and reflects being out of practice and adjusting to a new chase partner (Brad and I had this down pat). The second relates to wishing that I had set up a rearward facing GoPro mount, as the results would have been stunning running away from the storm. The third relates to the poor decision I made in over-ruling my navigator - she was damn right and would have got us out of there no problem, and probably kept us further from the 2nd tornado (there were other small tornadoes but only talking longer ones here). I think its unfortunate the storm occurred where it did - as I had planned several ways to skirt the OKC metro to the south, but hadn't considered a track like the storm produced (I thought things might set up further SW of the city and move NE initally and then E). In future I think I will be steering well clear of the Oklahoma City metro area on big days, and city areas in general - especially if mass panic evacuations induced by the media are going to become a recurrent feature.

'A Glimpse Below' - The dark wedge tornado is spread beneath the enormous mesocyclone, at this stage, likely at its widest. Difficult to really comprehend the size or intensity of the storm. Shot taken SE of El Reno, 5/31/2013.

The media induced mass panic (a broadcaster suggesting people should flee if they could not get below ground) was accentuated by the recent exposure to a high impact event (Moore EF-5). This basically left people in a state of terror that they too might be affected by a similar tornado - and when disorder reigns, most people struggle to cope. At the gas station near Chickasha people actually looked completely lost and unsure of what to do, in some cases this appeared to constitute genuine shock. Had the large tornado continued on its path or the second been larger or stronger, I think it would be right to assume that the death toll would have exceeded the worst tornado disasters in history due to the number of people exposed on the grid-locked roads, and rivaled some of the worst hurricanes. The sensationalist tendency of the media to over-emphasize the threat, even after the original tornado had lifted is something that really needs to be looked at - as with people in the state that they were, in some cases they actually ended up in greater danger. One could only imagine the repercussions if drivers fleeing on media advice were caught by a tornado. I think that additionally the evacuation management procedure if people do want to flee needs to be looked at - a good example is the policy and plan in place for bushfire events in Australia, which reduces the occurrence of such chaos. By the same token - part of the shock that people were exposed to was the uncertainty that their homes, families or loved ones were still there, and the lack of impact was poorly communicated by the media who focused on the negative aspects.

One thing that concerns me greatly is the growing number of locals and amateur chasers that have absolutely no idea what they are doing close to the storm and are recording it on whatever device that happens to be close at hand. As the impacts of this storm revealed, even experienced chasers can be caught unaware by a sudden change in storm behavior, and putting yourself in danger for something to talk about at the bar is probably not the smartest decision. If you are truly interested in chasing or severe thunderstorms - educate yourself. Try talking to someone who you have seen that chases regularly and asking them for places to look. Try joining stormtrack.org and learning from the extensive archive of knowledge that can be found there. And if you still can't find the information or where to look, please contact me - I would be happy to help point you in the right direction. As you can read in my previous post, alot of things were happening in the environmental characteristics that lead to it producing this tornado - and at least at a basic level this information can give us ideas about how we chase any storms that form. To find the way to best stay safe - do not put yourself in the tornado's path unless you are very aware of the potential consequences and behavior of the storm - and even then, think about what the storm might do in a worst case scenario and decide if you would still like to find yourself in that position. Forward thinking is essential to chasing storms - always plan your escape and re-plan it as the situation evolves; then, when the unexpected occurs, at least you have a way out to somewhere safe. Just don't leave it too late.

'Golden Wrapping' - Over gold wheat, the mesocyclone and the large tornado begin to rapidly wrap in rain, shifting northeastward before occluding. SE of El Reno, OK, 5/31/2013.

All photos are available for licensing or purchase, please contact John Allen by the menu above for pricing and details.

In Our Memories - the passing of Tim, Paul and Carl, and the Implications for Chasing from 5/31/2013

A large number of people have posted about the passing of Tim, Paul and Carl, and I think this reflects on just how well they were respected across the chaser and scientific communities. When the rumors started to spread I hoped it wasn't true - how could it of happened that they were caught in the line of fire.  I was in the field chasing on the day, and the fear that chasers would be caught was something that sat heavily on me. Once it was confirmed, the sinking feeling in my heart could not be described...I wanted to make a post about it and yet wasn't ready nor able.

Now that a few days have passed, and I have had time to collect my thoughts, I wanted to explain my feelings about this day and thoughts about its implications (My chase log will appear separately).

So here goes:

I first met Tim at a derelict gas station in Nebraska, and was struck by how easy going, approachable and honest he was. We had a very interesting chat about the storm that had failed to produce a tornado on the day, and talked shop about storm environments - like so many of us do when we are out on the plains. But Tim was different - when someone asked him a question they were never made to feel below him, in fact they left the conversation with a sense of awe and excitement. That is a rare gift to have, and it was far from his only talent - his wizardry for gadgetry and the design of probes for in situ tornado measurements was simply astounding. This would not be the last time I spoke to him either, from having a chat at a Denny's eating breakfast at 1am after a successful chase, and other times that were as simple as a wave or a polite hello.  The last time I saw Tim was on the dry-line last May watching 2012 produce yet another disappointment (which was later followed by the fail-recho). Tim was one of those who gave a good name to chasing - a gentleman chaser if ever there was. The way he modestly handled the public spotlight, and gave his all to promoting the science while maintaining the safety of his team had a deep impact on me and how I thought about chasing. One only need to watch an episode of storm chasers or a National Geographic special to see that he always put safety first, was level headed and a master of his craft. So why have I told you all this? I don't claim to be a close friend, or someone who knew Tim well. However, I considered Tim a role model, one of those that I could aspire to be like in the way that he never sought the spotlight, never put those he chased with in danger, and someone that could tie the experience of chasing back into the scientific and public domains. His ability to communicate to people at any level of knowledge is something that I think so many of us can learn from - talking to children in schools, the general public in libraries - the next generation of researchers, chasers and the future of public safety depends on this pursuit. I can honestly say that the world of research storm chasing has lost a champion who will be sorely missed.

I never had the pleasure of meeting Paul, but from every account he was a lovely person with a funny side, and from every photo that I have seen I think its safe to say an incredibly talented photographer. My thoughts and heartfelt sorrow go out to the Samaras family - to lose one is a terrible heartache, to lose two generations simultaneously is a sorrow that I can not even bear to imagine.

I only ever met Carl the once (well at least chatting to him directly), on April 8th this year at breakfast at a hotel in Great Bend. It was an interesting discussion on the day before, but I certainly would not say I had enough time to get to know him. Again, his reputation in many circles speaks volumes about the man, and he too will be sorely missed by chasers and scientists alike.


Now I would like to change tack, and look at the implications for chasing.
(Note for those who want to skip a lengthy discussion of the environmental parameters skip to the the next bold underlined text).
(Note 2: This is an expression of my interpretation, and others who are more familiar with significant or violent tornado environments may come to different conclusions.)

So what happened on Friday - how is it possible that four storm chasers were killed, after no deaths for what has been 40 to 50 years of people being out there? This troubles me, as Tim was so mindful of his surroundings and remarkably cool under the pressure of approaching tornadoes having been in the situation so often before. The environmental parameters that we saw last Friday were simply frightening and remarkable; The OUN (Norman, Oklahoma) sounding for 00Z shows Convective Available Potential Energy (CAPE) likely above 4000 J/kg before storm modification, storm relative helicity (SRH) in the lowest atmospheric layer (0-1km) in the 300 J/kg range, lifted condensation levels (LCLs) that were below 750m prior to storm formation. In this environment the threat for the rapid development of a tornado is incredibly high, and given the low cloud bases large tornadoes become more likely.

And yet this likely doesn't just encapsulate how volatile the environment was - so why is this the case? Well, surface temperatures that I observed at the lake in west El Reno prior to initiation were closer to 90F, while surface dewpoints in the Chickasha area prior to initiation were showing 77F on the mesonet. This yields a higher CAPE than the observed value at OUN 00Z - probably on the order of 5000 J/kg or greater effective (and this can be seen in the most unstable parcel for the 18Z sounding). Next, consider the influence of the storms motion - the storm during its early parts and initial tornado production was moving southeast - from an environmental helicity point of view this lengthens the hodograph substantially. Now, combine this with the east-southeast surface flow that could be found near the boundary of the triple point and we have SREH (Storm relative effective helicity) well into the "what the heck does that even mean" territory (300-500 or even more). Even in the profile above, the significant tornado parameter (STP) is in excess of 7, and the supercell composite parameter (SCP) is near 29 - NWS mesoanalysis paints these values at the time of both these values in vicinity of northern Oklahoma city and further westward towards the dryline/boundary intersection - possibly these were even higher by the time the storm began modifying the environment. While the 00Z 0-3 kilometer CAPE (a favored tornado metric) does not appear to be very large (45 J/kg) forecast values were suggesting this would move into the realms of 100 J/kg - certainly more than sufficient for significant tornadoes given the other parameters. Finally I would note that the deep layer shear is not very strong for the large amount of moisture, and given the relatively modest flow at 500-300mb, this suggested HP modes would be the end result.

Adding this crazy soup of parameters together indicates a few things - but lets compare it to the climatology. If you consider the distribution of significant tornadoes in the recent paper by Grams et al. (2012), surface dewpoints were above the 90th percentile for significant tornado events, and for surface temperatures - the resultant LCL height reveals that neither of these factors was a negative contribution, and only served to increase the vertical gradient and hence thermodynamic energy. LCL heights were low - certainly below the 75th percentile of the Grams climatology for the southern plains, while mixed-layer CAPE was above the 90th percentile - more like an environment in the Northern plains during the summer. 0-1km shear from the OUN sounding was near to the mean for the significant tornado sample, but it is likely that this is somewhat under-representative in the effective environment. Lets look relative to the local climatology for significant tornadoes:

Source: Screenshot of the NWS Mesoanalysis tornado segments for the vicinity of El Reno, OK, this is the product of work by Bryan Smith, Rich Thompson, Roger Edwards and others which can be found in a 3-part paper in Weather and Forecasting, 2012.

Effective STP - observed has it at the upper end of the distribution, SCP - is already out at the upper bounds, MLCAPE is in the very high range, effective shear over the depth is a little lower than the average but ramps up as we approach 00Z, while environmental helicity is near or above the 75th percentile. LCLs are also somewhat low relative to the climatology. (NOTE: This climatology contains only 26 samples, and hence may not reflect the full distribution of potential significant tornado environments for the area). 

Long story short, its pretty easy to see that we are looking at a type of environment that doesn't occur very often. We have very high available CAPE, low LCLs and significant wind shear and helicity in the near surface layers. Most of us haven't chased many environments like this - so lets think about potential implications to our storm mode and tornadic behavior:

1. Tornadoes in this environment are likely to develop quickly, be strong and have multiple vortex characteristics before wedging out. Here's a couple of events that spring to mind where the parameter space was pushed to the upper right of the distribution in terms of say helicity or CAPE: Joplin MO, Plainview IL. In each case you ended up with violent tornadoes with unstable or quickly changing vortex structures that develop rapidly. I'm not saying these are great analogues, but more just a couple of cases where I can think of similar tornado behavior.

2. With LCLs so low, you have the potential for the mesocyclone or tornado cyclone to potentially situate itself very close to the ground as a response to the rapid up-motion - with high values of environmental helicity meaning that spinups and strong vortices are likely, especially with such a strong mesocyclone. Consider as an example the Greensburg KS 2007 storm and its behaviour after dusk, or Hallam NE. There are probably other examples but I will leave those to people who are more familiar. The moisture that produces these low LCLs and the weak mid level shear tends to also push the mode towards the hybrid HP/classic structure, where the mesocyclone is still located in the SW quadrant of the storm rather than the east.

But what does this mean for those who chase? 

Storm motion from this profile will likely be pretty much to the east-southeast for right moving supercells - and I think many of us worked this out fairly quickly. Occlusion of the mesocyclone will be to the left of path - again pretty stock standard and expected. So where did we go wrong ? (I say we as even though I kept a respectful distance, I still found myself running rapidly east during the expansion phase to avoid the southeastward rear-flank downdraft surge and the tornadic circulation, though I was fortunately far enough south to stay clear of the later).

This opinion may not be the most popular, but playing the notch is like playing russian roulette - there is eventually going to be a time when the bullet gets you. I've held this opinion for some time (after nearly coming unstuck one day in Nebraska in a sparse road network), and in HP modes this tends to keep me at the very least further east, and more often southeast. In the past few years, we've seen time and again storm chasers who came close to being unstuck - a banged ego here, a shattered windshield there. But what happens on the day that you don't see the monster coming? People are no longer even chasing just the notch, but in under the mesocyclonic circulation - and in this case the tornado-cyclone. So in a low LCL environment, with a bucketload of helicity and no shortage of CAPE in the lowest layer - is that the right place to be? I'm not trying to tell people how to chase, just raise the issues and implications that we have to deal with after this event.

Now - in the case of the TWISTEX team, I don't have a single problem with them being there - this was what they did, and did so effectively for many years. I think (and this is a personal opinion only) some series of unfortunate events or timing (for example deploying probes, which is when they are at their least mobile) during the rapid expansion of the tornado-cyclone to the surface and turning of the tornado with acceleration northeast likely caught them out - with subvortices that had forward motions of 150 mph as documented by the XPol radar, they may not have even seen it coming, or were unable to do anything to get away. It is a testament to their mission and skill that they likely managed to deploy probes in the path of this tornado - a tragic but hopefully lasting legacy to tornado science that befits three of the great chasers.

For other chasers - maybe we need to reassess how we approach storms that are way out there on the scale of environmental parameters and question whether you want that particular tornado to be your last. The huge width of this tornado was definitely a surprise to us all as was the rapid movement, and reflected the combination of an incredibly strong mesocyclone and the available environmental energy and helicity. As Jon Davies pointed out, and from my viewpoint was also observable on the day - the tornado did not appear to be at the center of the mesocyclone, but rather closer to the periphery - which perhaps explains the increase in forward motion and change in direction to NE at 40mph when combined with the RFD surge to the southeast.

In a different set of circumstances - this could have been much, much worse - the secondary mesocyclonic signature could have also produced a strong tornado tracking southeast into the panicked masses - leaving storm-chasers with no escape. Or perhaps the primary mesocyclone could have continued moving southeast at increased speed overtaking more chasers as it expanded, fortunately the RFD surge probably prevented this. My girlfriend/navigator was in the right hand seat on the day, and showed me the horrific image of spotter-network icons that were either in the path or very close to the very strong mesocyclone - and I was terrified that we would lose many more than we did.

So where does this leave me - I don't think it will stop me chasing, as many proved that this circulation could be safely navigated and documented with incredible images and data coming to light. However, I think that I will certainly think twice about what the environment means on a particular day before chasing - a lesson that I think would serve many aspiring chasers to the field well. I extend my deepest sympathies to the families of all the victims, both non-chasers and chasers for your loss, they will be missed by all. But as a final remark, here is a plea to the chasing community:
'If you value Tim, Paul and Carl's memories, then think more about the implications of the environment on how you chase, how it reflects on each of us when all is done and dusted - Tim, Paul and Carl were always very conscious of chasing safe. Please don't sacrifice your life in pursuit of that one tornado shot - it is never worth it, the chaser community needs no more funerals.'





This post was written by John Allen, and all the opinions and speculation are his own and do not reflect those of others involved in the Hunters of Thunder.


 
Reference:
Jeremy S. Grams, Richard L. Thompson, Darren V. Snively, Jayson A. Prentice, Gina M. Hodges, Larissa J. Reames. (2012) A Climatology and Comparison of Parameters for Significant Tornado Events in the United States. Weather and Forecasting 27:1, 106-123

Smith, Bryan T., Richard L. Thompson, Jeremy S. Grams, Chris Broyles, Harold E. Brooks, 2012: Convective Modes for Significant Severe Thunderstorms in the Contiguous United States. Part I: Storm Classification and Climatology. Wea. Forecasting, 27, 1114–1135. doi: http://dx.doi.org/10.1175/WAF-D-11-00115.1

Richard L. Thompson, Bryan T. Smith, Jeremy S. Grams, Andrew R. Dean, Chris Broyles. (2012) Convective Modes for Significant Severe Thunderstorms in the Contiguous United States. Part II: Supercell and QLCS Tornado Environments. Weather and Forecasting 27:5, 1136-1154

25/5/2013 - The Return to the Plains

The Hunters are back - who knows what happened to the Australian season (well until John left anyway - thereafter there seemed to a be a surplus of tornadoes), but this seemed to translate to the plains for the early portion of the US chase season as well. Only two systems of any note for all or April, producing barely any tornadoes and certainly not living up to expectations. John & Rose's chase for the 7-10th netted 3 supercells and perhaps a weak vortice, one tornado warned storm and some really nice structure. The low-lights were really being chased out of Oklahoma and Kansas by freezing rain (one of the stranger experiences of John's chasing career). 

As of today, both Brad and John are back on the road - though on opposite sides of the plains. This next week, we will be covering storms from two vehicles as a reasonable 500mb low pressure trough transitions across the highs plains. Updates will be coming regularly, and while we have a slight change in web address for the short term until the new hosting comes online (note we can now be found at http://www.huntersofthunder.blogspot.com/ ) we will keep you updated with the action. The very much delayed chase log from April will also be online soon.

Forecast Bust?

A really important aspect of chase forecasting for me is post analysis: what was the environment saying, and what did the atmosphere end up doing (comes back to my research). So I made the call that yesterday should have been chased, and went with a target of between Swan Hill and Balranald. How did my forecast go? Well heres a radar 128km loop from Mildura showing storms forming on the day.
See : 128km Radar Loop for Mildura, 05:00 12/07/2012 to 16:00 12/07/2012 UTC

And the 256km loop which shows my target area clearly:

See : 256km Radar Loop for Mildura, 05:00 12/07/2012 to 16:00 12/07/2012 UTC

 

So its pretty obvious when we look at it that the atmosphere didn't pan out quite like I thought it might. Or did it? You might notice the cell that forms near Robinvale NSW at around 6:30GMT (4:30 pm), which initially moves south but then turns hard east around 7:30pm local before anvil debris from a cell to the north interrupts its lifecycle (note that Mildura is an under-reading C band radar, and is notorious for showing far weaker echoes than the storms actually occuring, so red/orange is quite impressive). The deviation to the mean flow (some 45 degrees) and longevity (at least 2 hours as a discrete cell) would suggest that this was a likely left moving supercell. In fact a number of the cells show the tendency to turn to the left of the flow in the northern sector, until a pesky right split from one of the three initial cells kills the cell heading for Mildura and causes a multicellular collapse, and a second right split from the northeast cell kills the middle of the three. So looking back on it actually the forecast was pretty good - we were looking for organised, rotating storms and found them, but unfortunately without enough capping we ended up with too many storms which had some interaction issues. 

So why were the storms forming in these two areas, here is the 00Z forecast from GFS for 5pm. 

Hang on you might say, that looks very different to the forecast this morning - You are right, the system has retrograded further west into South Australia. A quick look at the CAPE at 00Z:

 So the Instability is still in Victoria, despite the shift in the upper system, but shifting the upper system might have changed the shear - so what if we have a look at 06Z: a 4pm close to analysis:

The instability is smaller than forecast and shifted northwest, so less energy is available for the updrafts, perhaps explaining the tendency to collapse as the cells moved away from the favourable CAPE towards the southeast.

So the next question is why were the cells splitting to the north, but the southern cell near Robinvale didnt? The trick here is to have a look at the environment present. Lets check a 18Z forecast sounding for 4pm near Robinvale:

The key features to note here: Instability is lower (explains the compact nature of the cell), and the shear bends 45 degrees from North/NNE to NW and strengthens with height: a favourable (though not as strong as forecast) shear environment for let moving supercells. So lets look at the environment the northern cells were 'seeing'.

Ahh, we have moderate unidirectional shearing of the atmosphere, with relatively higher bases (taller LCL) and more instability. So what was this going to do to the storms? Cause splitting as both the left and right rotational couplet of the supercells are equally favoured by this sort of wind regime. When you end up with cell interaction you never know what you will get (a monster or a collapse) so in this case the interactions killed the cells, and with balance not quite right any attempts at being a supercell were pretty transient. So in conclusion, the forecast based on the data available was a good one, (20/13 was seen in Mildura) but the evolution in the atmosphere wasn't quite right to produce the strong storms we were looking for, so I'm a little glad I couldn't chase but at the same time disappointed as its always interesting to see what evolves in different environments. What is interesting is the storms in this area weren't the most impressive of the day. In fact check out this sounding east of Adelaide: 

Boring and capped you might say? Well, it has reasonable turning and ok deep layer shear of around 45 knots, but why am I mentioning it as it has little CAPE and looks like it has no chance of producing storms. If you look at this radar loop though:

See : 256km Radar Loop for Adelaide (Buckland Park), 02:00 12/07/2012 to 16:00 12/07/2012 UTC

 

Whoah, suddenly we have strong storms, and supercells forming amongst them. But how? The environment wasn't really primed for that, or was it? I draw your attention to the area between Maitland and Port Lincoln at 12pm, and subsequent scans - which shows a gustfront boundary with preferential lifting along its axis, and though not visible on the radar scans (probably due to scan height), it extends to the area east of Adelaide. So what has happened because of that boundary? Clearly cells have been initiated by the additional lift, but additionally the Storm Relative winds have been increased - in effect the forecast shear looks nothing like what the storms saw on the day, and the resulting development was favourable for organised rotating storms and where things were too clustered, multicells. The lesson here is: forecasting for a chase will only get you so far, what the atmosphere realises can be worlds apart from that forecast that you thought was perfect. It is really important though to analyse why your forecast didn't (or did) pan out as pattern recognition improves your forecasting markedly (though not every day will pan out the same with the same conditions) Adapting to mesoscale features (such as boundaries) on what might appear to be marginal days will definitely make you a better chaser, so keep your eye on the observations and the skies. 

Oh and was my forecast a bust? Not sure which way to call this one, while storms formed and organized as I expected it would have been a long drive for just that Robinvale cell - but it could have been really spectacular and worth it. You be the judge, tell us what you think on facebook or in the comments below. 

John

A Somewhat Bizzare Looking Setup 12/7/2012

Have been keeping tabs on this system quietly for the past few days, wondering whether the models were taking a holiday or something was really going to pop up and yield some storms. Just to recap, its the middle of winter, most days have been 13 degrees centigrade and rather poor in Melbourne. So what the heck is going on in this chart below? Minus 5 Lifted Indices - in mid July?

Meet the implications of a reasonably strong trough and developing low which has managed to advect warm surface temperatures and moisture south into Southern NSW and Victoria. A quick look at an observed sounding yields quite a favourable profile for organized convection (and possible severe).

Of particular note are the surface temperatures (19C) and the dewpoints (~12C). So even though we are in a predominantly cool season - the relative warmth of the surface air has yielded an unstable environment. CAPE values max out at around 1000 J/kg based on surface parcel trajectories (mixed-layer shown), with substantial vertical wind shear in both the 0-1km and deep layers (~20 knots and 66 knots over the deep effective). This environment is reasonably favourable for rotating storms and supercells.

Now on to what is wrong with the environment. Storms fired overnight through South Australia, and while early morning convection did traverse the target area, I don't believe it will substantially alter the environment given it passed through early. The environment is also fairly heavily capped until the mid-afternoon, but it does appear that initiation will occur sometime during the diurnal peak. There are also the usual questions about effective moisture available to storms, as GFS tends to be a bit exciteable. On a gut feeling I would say chase today (but I have been known to go out and look purely because I am fascinated by odd setups regardless of implication). My target would be between Swan Hill, Victoria and Balranald, NSW. So will be watching closely to see how the forecast goes...

So this begs the question, why am I telling you about this? Because I can't chase it! Unfortunately the Hunters of Thunder are a man down today so will have to let this one go - its too far for a single man effort with limited light and this PhD needs finishing before chase season really gets rolling. Oh and for a little humor from my friend Skip Talbot:

Hunters of Thunder 2011/2012 DVDs now shipping!

Hey Everyone,

Before we get to the end of US chase wrap up I thought I would let you all know that our 2011/2012 Australian Chase Season DVDs are now shipping. We've dispatched a bunch of orders already, and are still waiting on yours, so either click the DVDs tab above or visit: www.emanatephotography.com/hunters.html

We have two trailers out for the DVD which can be viewed below:

The DVD is a awesome smorgasboard of photography and video highlights from out very active chase season, with 10 awesome chase days including events like the Haymaker:

and Melbourne's Christmas Hailstorm:

Together with nearly 4 hours of high quality (Dual Layer DVD) chasing footage from around the Southeast of the continent.
We also have just released a second trailer for the DVD. It includes a look at the menus and just some of the stuff you will see if you get your own copy:



To Order yours now, click Order Now or contact us via email and we will sort you out with a copy. Internatonal orders may take a little longer but will be dispatched via airmail upon receipt. Price of the DVD is $30 AUD shipped anywhere worldwide. Payment is via Paypal, Credit Card (using secure paypal service, no account required) or by Direct Deposit upon request.

Short Analysis of the Black Ranges Tornado, Victoria, May 24th

On May 24th there was a tornado observed near Stawell in the Black Ranges, Victoria. I generally like to keep track of local happenings, and this particular event took my interest.

A photo of the tornado from a local resident. It was accompanied by hail. Photo Source: Stawell Times

Further details of the observation can be found here: Stawell Times
http://www.stawelltimes.com.au/news/loc ... ?src=email

A radar loop of the event can be found by clicking below, note the cell near Stawell and Ararat between 2pm and 5pm local time.
http://www.theweatherchaser.com/radar-loop/IDR022-melbourne/2012-05-24-01/2012-05-24-10
Based on radar analysis, it looks to me to be a left moving type supercell storm ( intially I had my doubts and thought it was right moving intially), but if you look carefully between 2pm EST, and 4pm you can see the cell actually move left of the mean flow from Stawell to Ararat. It seems like the cell initiates around 2pm, and disapates/gusts out around 5pm after generating a right split. Three factors therefore convince me this was a supercellular tornado - longevity, deviant motion from mean flow and splitting behaviour. There is also some indication from the eyewitness that the storm was very much tornadic, with the tornado not being that short lived : "Then suddenly it deviated away to the right, broke down and formed another small twister in a neighbour's paddock.", this would suggest an unstable vortex phase or possibly a second tornadic circulation. From the lifting/damage described (particularly trees ripped out and moving the toolbox) I would estimate it was probably an F1. There is also some indication that largish hail was also present within the storm given the mentioning by the resident, and this was likely a result of the supercellular processes at play (which with extremely cold uppers can overcome the relatively low instability).

The maximum temperature on the day was 13.9, but a 3pm observation at Stawell aerodrome gives a 11.9 degree temperature with 85% RH and southeasterly surface winds and a surface pressure of 1011.7hPa. A quick look at the synoptics suggests an incipient low pressure system located in NW Victoria as of 00UTC, with a trough to the southeast, forming in the preferential post-frontal air mass (typically the unstable airmass following a frontal passage on the equatorial side will lead to secondary cyclogenesis).

By 06UTC the surface low had deepened to 1009hPa suggesting cyclone intensification and a slight move to the Southeast.

Checking the radar we also can identify that the cells death was preceded by a shift of wind direction at steering level to northeasterly while prior to this motion was front the north. Based on the trough observation from analysis, and this behaviour we can conclude that the cell was initiated by the trough, and developed in a favourable pre-trough regime (almost warm-front like from the moisture observations).

Looking at the upper air information at 00UTC:
700mb:

500mb:

This tells us that the environment was characterised by steep lapse rates, with temperatures of 11.9 at the surface, 0 degrees at 850hPa, -9 by 700hPa and -30 by 500hPa. (note this was about 4 hours earlier so lapse may have been greater). I've been unable to get my hands on an upper air sounding due to the university of wyoming being down, but Melbourne wouldn't be particularly representative anyway due to its position relative to the front and the different flow (noticeable on radar). Based on a little work with my spare skew-t (have a laminated one in my office), I would estimate that LIs were probably  in the range of -1 and -2 between surface and 700mb, and CAPE would have been sub 200 J/kg. Given the extremely cold uppers and the local low, It would also seem that the storm tops were not particularly high.

The shear characteristics are very hard to work out without an upper air sounding, but the radar and surface observations give some clue. Surface observations were southeasterly that fits with the presence of the trough as the initiating boundary, and is also the direction the storm ended up moving, and hence the cell likely enhanced its storm relative helicity (tendency to spin) by doing so. General motion of cells without deviant behaviour was to the south, suggesting overlying northerly flow. Motion of cells not deviantly moving was of the order of 25-30 knots which would suggest at storm steering level (around 700mb) that we had 25-30 knot northerlies at least, possibly more. Overlying shear was probably much stronger given the type of environment, and a quick look at 300mb yields:

A strong northerly jet on the lee side of the developing cyclone. Based on this information, we therefore know we had an environment highly conducive to left moving supercells, with turning from SE to Northerly shear vectors producing useful helicity to any storm that developed.

This leads me to my final analysis: This event was a cold core tornado that was produced by a reasonably long lived, left moving, low-topped supercell in a low instability, highly sheared environment. The environment for the cells lifetime was characterised by high relative humidity (85%), low instability (sub 200 J/kg CAPE, but -2 LIs in the 0-700hPa lift), and reasonably high cyclonic shear (likely in excess of 50 knots). These conditions are perfect for the development of low-topped supercells, and given the relatively low LCLs, turning within the cell along with helicity increases due to motion into the surface inflow, and low level instability associated with high lapse rates, it is little wonder that it produced an F1 tornado. These systems are relatively typical for postfrontal airmasses or in the vicinity of low centres in southwestern Victoria (See Coloquhuon et al. 2008 and other studies).

If you are interested to know more, please leave a comment or question.
John

Acknowledgements: The Bureau of Meteorology for synoptic analyses, The Weather Chaser for radar loop and the Stawell Times for the photo.

June 7th - Collosal Colorado, rinsed and repeated.

After playing with a tornado warned storm and the largest quantity of hail (over such a large area) I have ever seen the night before I began my day in Denver happy in the knowledge that I was likely to see a repeat showing of slow moving storms with possible tornadoes, large hail and most importantly supercell structure!  For the second day running, the Denver cyclone and converging winds off the Palmer Divide would not dissapoint.

It appeared to me that there were two legit targets for the day; one in the NE corner of Colorado and pushing into SE Wyoming where easterly surface winds and relative high dew points in the mid to high 50's were being drawn in by the Denver Cyclone effect, while the second target was the Palmer Divide where storms often fire and move east or south east into the plains.  I decided to play the NE target first where storms were likely to fire earlier and see if they became tornadic before heading for the south target once things got messy up north.  I moved to Fort Morgan once again but before I finished the 90min trip from Denver, a tornado watch was issued for the area and a storm in SE Wyoming (about an hour to my north) was already showing signs of producing a tornado (which it did).

Sure enough storms fired to my SW and I moved to intercept south of Wiggins where I saw early and brief signs of supercell structure and got hit by golf ball hail and torrential rain as I core punched several times.  The storms in the area were again moving NNE like the day before and radar showed some strong rotation in the upper and mid levels and it seemed the storm may go tornadic however it split and the preferred right split did not survive with the left split dominating leading to low visibility and a lot of rain = no fun.  In the meantime storms were firing off the Palmer Divide about an hour to my south so I made the same decision as the day before to abandon the NE mess and head south.

The main storm of interest soon became a supercell and dominated its environment and I recieved messages from John regarding its behaviour on radar and reports of rotating wallclouds and funnels as I drove......with purpose.

Once I closed on the storm from the NE I could see the tell-tale signs of a monster supercell that was going to be worth the effort and I quickly gained position on the interstate to the west of Limon as the storm moved south at 5-10mph.  Similar to the day before I could see the base, wall cloud and interesting lowerings on the forward flank to my west. 

The first view of the low base features to my SW near Agate, Co.  Photo: Brad.



Surface interaction was evident as the forward flank produced weak funnels and kicked up dirt.  Photo: Brad.

Today I decided to go straight at the monster and get close so I went west to within about 500m and then paralleled the storm southward with incredible views of the most intense broad rotating structure I have ever seen up close. And then there was the beaver tail and 100km/h inflow winds to boot. Wow - what a storm, and I knew that the mid level and upper structure was likely epic from a distance but you cant be in two places at once. Photography and video was difficult do to my proximity and the insane inflow that made it difficult to stand upright but you get the picture from the shots I did get.

Direct intercept! heading west at the slow moving supercell.  The beaver tail is developing above me as a ghostly white lowering can be seen in front of me.  Photo: Brad.

The broad rotation of this storm was something quite amazing.  The white low level cloud in the photo below was ripping left to right around the storm so quickly, hopefully I got some video of it amongst the chaotic wind and excitement.

Awe inspiring low and mid level structure at this stage with 100km/h inflow and incredible broad rotation up close now.  These are wide angle shots! Photo: Brad.

I was so close to the storm now that only wide angle lenses could begin to capture it and even then it required panoramic photos and stitching software to begin to do it justice.  It was a challenge to photograph due to the conditions but below is a crude stitch that gives some idea of the structure.

Stitched wide angle panoramic (5 shots) to demonstrate the structure. Note the 2 wall clouds and RFD.  Photo: Brad.

As I drove south in parallel with the storm a strong persistent cone funnel emerged to my west but I was unable to confirm a tornado myself despite other reports in the area.

A possible tornado to my west but I couldnt confirm touchdown from my position.  Photo: Brad.

I found my way south to a west road and went closer again, this time with 100m of the advancing hail shaft that was now an irridescent blue colour and contrasted with a magnificent, strong bright white beaver tail almost overhead, that was intersecting the mesocyclone from the east. You dont get much closer to the business end of a monster HP supercell than this - without getting smashed by large hail or a tornado. I allowed the storm to advance on me until the last moment where I had my GoPro wide angle camera mounted on the back of the car and then I fled eastward for a south road.

Beaver tail!!!! moist easterly inflow feeds directly into the mesocyclone as the core advances on me west of Limon.  This stitched pano is comprised of 7 wide angle shots and that core is only 200m away!  Photo: Brad.

I was less then 5mins into my east move when I just had to see what was behind so I took a shot out the window and was so blown away by what I saw on my screen I had to stop right there!  exposed ringing supercell structure all the way into the upper levels and a clear view of the beaver intersecting the mesocyclone. Add to that the menacing dark shadows under the storm where I had just come from and it was a chasing moment I wont forget.

Okay, so picture this....Im bailing east to avoid getting smashed and I turn to look out my drivers window to see this behind!
Photo: Brad.

Wide angle stitched pano (7 shots) west of Limon.  Photo: Brad.

I finally hit a south road and blasted along to get into position for the final moments of light as the supercell took it's exposed structure to Another Level (yes that does have a meaning).  The beaver tail from the east was one of the longest I have ever seen (the extended length is not captured in these photos) and the exposed mesocyclone at sunset was simply extraordinary.

Just about speechless at this point.  Structured supercell with monster beaver tail at sunset north of Rush.  Photo: Brad.

Okay, speechless now!  Photo: Brad.

Colours and a new tornado warning on sunset, stitched pano taken near Rush.  Photo: Brad.

The supercell continued its incredible rotation after dark and made several attempts to tornado with sunset backlighting.  Photo: Brad.

The supercell continued slowly on its way south and was again tornado warned (and for baseball hail) just after sunset as it's incredible rotation continued.  I witnessed several wall clouds and areas of focussed rotation after dark near Rush, with lightning illuminating the structure and one weak funnel.  Eventually I called it a night and headed toward Limon for data and to make some big decisions about the remaining days of my chase trip.