Double Dryline

07 May 2014

After a lazy wakeup and a badgering phone call from reception, informing us check out had been and gone, we got our act together and got on the road for our second chase day. The setup was another slight risk of severe storms initiating off the forecast dryline stretching from southwest Oklahoma into North Central Texas. We opted to head to Seymour, TX which was only a little west of where we stayed, hence the late wake-up.

We weren’t waiting in Seymour long before a mesoscale discussion was issued by the SPC. This being the Storm Prediction Centre and the guys who issue the daily to 8 day outlooks for convective weather across the entire country and who we rely on as a resource for forecasts and current observations – all of which is free and available online.

A mesoscale discussion is the discussing of a potentially severe situation that is forecast to happen in the near future. Within the discussion, the probability of a proceeding ‘weather watch’ is also issued.  This probability denotes the likelihood that the situation will occur. A watch will then be issued if the said forecast situation actually arises. A ‘watch’ can be issued for either ‘severe thunderstorms’ or ‘tornadoes’, but the ‘severe thunderstorm’ watch is always caveated with the fact that tornadoes cannot be fully ruled out.

A mesoscale discussion usually covers a much smaller area than the initial risk area, so to have one issued very close by is exciting and means you have a good chance of being able to get on the storms should they arrive.

The current discussion was due to the identification of a double dryline just to our west and the beginnings of convective initiation. The dryline is a common feature in this part of the southern plains and marks the boundary between the warm moist Gulf air to the east and the cooler dryer air off the Rockies to the west. This boundary can be variable in strength but is often a reliable source of ‘lift’. In a nutshell, warm moist air requires ‘lifting’ to a height at which the moisture will condense into cloud.

Today however, we were faced with a double dryline. There were in fact 2 boundaries separating warm moist air from cool dry air to the west, and this from even cooler dyer air even further west. The storms initiating on the dryline furthest away looked the most tempting on radar so we headed there first but soon realised that the potential for becoming stuck between 2 lines of storms was highly probable so retreated back to the initial line, where the storms here too were beginning to develop.

At first, there was nothing incredibly impressive about what we saw. The storms were fairly linear – all forming in a line and there was little to see that was particularly distinctive. It was all just a bit grey. What we did manage to find however was a couple of chaser friends from England – Paul and Aaron who run tours out here throughout the season but were having a few days off to play around in the storms before the first group of tourists arrive.

After a quick catch up, they decided to head north, but we held fire, not totally sure whether it was going to be worth following the rather non-descript looking cell north and instead waited for another we had seen on radar as it approached us from the south looking far more discrete – which is better for seeing storm structure.

Although saying we waited isn’t exactly right. It’s really hard to wait. You get itchy feet. What we actually did was we headed south to meet it, before then having to take a turn west to get behind it and then ended up chasing it back north to more or less where we were an hour ago. It did give us a few more photo opportunities though!

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As we followed it north, it became more photogenic and the base appeared to be lowering, which is great news as it could result in the storm locking itself into the warm moist boundary layer air, increasing its tornadic potential.

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At this point, we were together on the road with many other chasers. We were even the filling of a ridiculous dominator sandwich with one of the famous vehicles both in front and behind us at one point. I have to add, they were both behind us initially, obviously waiting to see what our next move would be! This was a popular storm, but we managed to take a side road up to a dirt track where it was a bit more peaceful.

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We stayed with it for a while, but as the light faded, so did the storm unfortunately. Further to the west however was another storm that had already put down a brief tornado, but was still growing and it was possible if we kept heading north, we would intercept it in its path. This is what we managed to do, the structure was breath-taking and we were in a great position to watch it approach for a good 10 minutes before we had to move to a safer place.

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That safer place however was a little more difficult to get to than we thought it would be. The amount of other vehicles on the road meant we had to wait at traffic lights and crossroads for longer than we would have liked. There was this big supercell on our tails, the whole area was becoming shrouded in darkness and to top it all off, they issued the tornado sirens from just behind us.

It was at this point that came the all too familiar feeling of ‘oh god, why have we got ourselves into this position again’ as I battled with keeping calm versus the need to hold my camera with shaking hands out of the window not being able to stop looking up at the imposing storm on our tails and repeatedly saying to Tim who always drives in these situations ‘you wouldn’t believe what It looks like out there’ whilst excitedly, yet anxiously trying to show him the blurry shot on the back of the snappy cam.

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Luckily we got out of the path in time and the whole experience was another amazing one. Once out of harm’s way we pulled over for a few more quick pics before heading to a nearby Walmart car park in Ardmore, Oklahoma. There, with a beer in hand whilst sharing a can of beans, we sat in Escapey 3 trawling through our photos and looking at tomorrow’s models until the early hours. A great second chase day.

SPC Day 1 Weather Outlook as at 06:00UTC (01:00 Central Time the night before)

SPC 01:00UTC day 1 forecast for Wed May 2014

SPC Day 1 Weather Reports for the day.

SPC storm reports for Wed May 2014

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