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.



June 6th - Fried rice with cashews, tornadoes and a Colorado classic

After dropping a subdued John at Denver airport and checking the models and SPC forcasts, it was very clear I would be targetting the front ranges of Colorado the next day so I headed for Fort Morgan for the night and some Chinese fried rice with cashews.

The morning of the 6th saw me in a 5% tornado risk area before I even got out of bed!  There was a Denver cyclone developing and combined with upslope flow and the potential for storms to fire off both the Palmer Divide and the Cheyenne Range, the day was looking full of promise.

So, as you do when you are already in your target area at 10am, I headed off for fuel, food and a Maccas to pass the time until storm initiation.  After several hours of not seeing any other chasers in town, the convergence began including several doppler on wheels radar units and research teams.

Eventually storms fired to the west nd were moving slowly NNE.  I held back within view and watched radar as others raced north but I was unimpressed by the storm motion and what I was seeing.  I was waiting for a right mover or a cell to break away from the NNE motion and feed on the easterlies being pulled in by the Denver cyclone.

After following the initial cells slowly north I decided that the only sure bet for supercells this day would be to take a punt on cells developing an hour or so south off the Palmer Divide so I turned my attention that way and drove south for an hour.....and what a decision!  As I approached my revised target area and had a slowly south moving storm in view, I was alerted to a tornado warning to my SW near the southern outskirts of Denver and another chaser convergence was underway including the Dominator tornado intercept vehicle and support vehicles.

Soon I was in position to see the solid base features and dynamic nature of this supercell which persistently produced funnels and lowerings on the forward flank as it was really getting ramped up.  I captured a possible brief and distant tornado (perhaps a landspout) in this early stage as the storm structured up, developed a long inflow tail from the east and went nuts on the moist easterly inflow. 

The first view as I head south onto the near stationary supercell with solid RFB and forward flank lowering.  Photo: Brad.

This possible tornado (or landspout) was persistent & one of several early features on the forward flank of this storm.  Photo: Brad.

Not long after I noticed a large wall cloud area organising to my west and a clear slot was evident cutting around it. 

Structure!  The storm was barely moving but had impressive inflow from the SE as a wallcloud forms.  Photo: Brad.

Sure enough, a tall elephant trunk tornado formed right next to the wall cloud (but not from it) and was on the ground for over 5mins. Interestingly, as the tornado roped out and lifted the wall cloud area seemed to grow larger, take on a cone shape and lower toward the ground. To me it appeared to be a large cone tornado and perhaps even a wedge. To further enhance my thoughts on this being another tornado, the entire area finally lifted and what I thought initially was a wall cloud went through a significant rope out and I have never seen a wall cloud rope out before........... interesting.

The storm produced tornadoes, flash flooding and then simply ridiculous amounts of hail as it moved ever so slowly over the next few hours.

A tornado is forming as a clear slot cuts around the dark wall cloud area.  Photo: Brad.

A tall elephant trunk tornado persisted for over 5mins to my west as I was driving south for position. Photo: Brad.

The tornado begins to rope out but is still quite large while the clear slot is cutting further around the adjacent wall cloud.  Photo: Brad.

Spectacular structure as the entire wall cloud area is now roping out which leads to a few questions..... Photo: Brad.

Wow!  Mammatus clouds on the forward flank of the storm were persistent like this for over half an hour!  Photo: Brad.

Large areas of dust/dirt were lifted into the storm base to my west.  In this case a large funnel is curving back into the storm.  Photo: Brad.

I eventually core punched the storm into southern Denver and had fun with the crazy hail drifts for a few hours before chasing a new tornado warned storm through the SW suburbs at midnight! I saw the wallcloud and obvious signs of rotation on this storm lit up by city lights and constant lightning before this storm turned into yet another slow moving hail machine that turned the suburbs into a land of white ice like i've never seen before. At one stage as I core punched the hailer through a technology and business park, I came across rescuers who were pulling other cars out of several metres depth of ice and they told me they had already rescued 7 others. There was nothing I could do to help as the roads around me became rivers so I turned around and called it a night.

Later that night, Denver's SE was smashed by near stationary severe storms and ridiculous hail quantities.  Photo: Brad.

After chasing all day, how about a tornado warned storm in Denver at midnight?!?!  Photo: Brad.

A quick check of data for the next day showed that I wouldnt be going far.  Could Colorado do it two days in a row?  Of course it could!  ........and even better :)

May 29th - Oklahoman Wonder

After a bit of a disappointment in Texas the previous day, we set our sights on Oklahoma where a good environment for supercells appeared to be in the offing. With strong deep layer shear, and moderate to strong instability combined with reasonable dewpoints, tornadoes were a chance and structure would hopefully show itself. We targeted El Reno, OK, and sat in the incredibly oppressive conditions - 100F (38C) with mid 60 degree farenheit dewpoints for some time waiting for the southernmost storm to get its act together. Eventually the storm transitioned from a more multi-cellular appearance into a nice supercell, which we closed in on as it structured up.  Wide angle lenses were the order of the day from here on in!

'The first view' as we approach from the south and then flank the storm to the east to get into prime position.  Photo: Brad.

'Barrel Ahoy' - The structure reveals itself from the murk as the supercell begins to structure over the fields near Loyal, Oklahoma. Photo: Brad.

And what a structure! 3 tiers and exposed to the world with the fields of Oklahoma stretched out below it. One of those simple wow moments that you just love to have when chasing!

'Wedding Cake' - A classic 3-tiered supercell mesocyclone reminiscent of a wedding cake floats like an impossible creation over the plains. Photo: John.

Wow!  Says it all really.  Photo: Brad.

The rotation speed within the storm was insane, almost dizzying with multiple areas of strong rotation and a closely proximal anticyclonic rotation as well. We went in relatively close (at the expense of structure) for the chance at a decent tornado when the wallclouds came down, but unfortunately early on the storm remained relatively high based and only produced a few weak spinups that were confirmed by other chasers as 'tornadoes'.

'The First Attempt' - Strong elevated rotation but not with the wall cloud to match, the first strong attempt at a tornado manages to generate some weak surface circulations. Photo: John. 

'Another Lowering' - The supercell continuously cycled, with RFD cut being followed by yet another strongly rotating wall cloud a number of times. Photo: John

Racing south to keep position, this was the view from the drivers seat! Photo: Brad.

What was far more impressive was the size of the hail being produced by the storm, hailstones were reported to Grapefruit size (5", 12.5 centimetres), with some allegedly up to 6 inches! Fortunately we managed to keep ourselves out of trouble with the gorilla hail core (though 3 inch stones smashing on the road and bouncing over the car were a little close for comfort), and kept good position on the cell for a couple of hours, until it decided to go bananas upon collison with a left moving supercell near Piedmont, on the outskirts of Oklahoma city. The result was an incredibly structured new cell with strong rotation that produced a weak tornado and some pictures that I don't think we will ever forget. 

Tornado! Dust is raised as a dark funnel emerges near Piedmont north of OKC.  Photo: Brad.

'Wrapped In' - The tornadic circulation is quickly wrapped within the monsters precipitation. Photo: John.

'In full flight'. The beast is capable of producing tornadoes and at least grapefruit size hail. Photo: Brad.

'A Monster Unleashed' - With the impetus it now needed to go ballistic the new supercell quickly went HP and wrapped its core circulation while producing a tornado. Note the unusual filtered halo on the right. Photo: John.

'Greenage' - The sinking sun and the giant hail within the storm gave an interesting optical effect in producing the most eery green glow through the clouds. Photo: John.

Chasers become the chased.....by giant hail!  The view behind as we run.  Photo: Brad.

We then proceeded to play with the hail cores on the western edge of Oklahoma city as this cell and numerous others trained over the area. We encountered a few stones above tennis ball size, but unfortunately couldn't catch the grapefruit producer through the metro.

'Decay' - With the excitement of the collision now over the cell quickly ran into an unfavourable environment and fell apart in front of our eyes on sunset. Photo: John.

'A Certain Kind of Light' - The lightning didn't really happen for us on this day, but still offered some interesting photographic opportunities if you knew where to look. Photo: John.

 All in all a fantastic days chasing, and exactly what bring us to the states effectively the 'tail-end charlie' and amazing photo opportunities with a gorgeous storm. Still looking for that amazing tornado though.