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Historic Thunderstorm Flood Event & Claudy Bridge Collapse - August 22nd 2017

On August 22nd N. Ireland experienced one of its worst thunderstorms in years which generated a widespread severe flood damage event which will go down in weather history. An unstable plume of warm moist air in a SEly flow advected across the country with 800 + convective available potential energy and a lifted index of -4. A cold front moved in from W at a very slow pace, forcing from the front and trough with cold air aloft (eroding a capping inversion) made for the perfect ingredients for high precipitation thunderstorms. 30 knots of 6km shear would tilt updraughts, the result being organized long lived cells with slow storm movement and with models indicating unstable air over land as late as midnight (rare) the potential was there for thunderstorms to thrive well beyond sunset and into the night. These storms where not rooted at the boundary and hence not surface based in nature so they posed no threat of tornadoes. However these storms did become elevated, which meant they formed higher in the atmosphere with very high bases. These kind of storms pose a high risk of frequent and dangerous lightning with an increase in positive c-g bolt events which can cause structure damage and a life threat to persons and livestock. Furthermore precipitation from these high bases falls from a greater height and hence stronger force occasionally accompanied by strong downdraughts or microburst type phenomena.

Storms fired during daylight hours in the S and slowly advanced N over the border into N. Ireland where they became widespread. During daylight hours elevated storms tend to be unphotogenic with no structure so I decided not to chase and just watch from home, however at night these storms are a different story capable of mesmerizing light shows so I was waiting for the sky to darken. Storms affected the county all evening, I watched good lightning from Maghera including overhead in-cloud bolts and loud cascading thunder with heavy rain.

As I said earlier elevated storms in daytime posed no photogenic potential so I never went out chasing and stayed at home in Maghera with the windows open listening to the sound of heavy rainfall on a muggy evening while enjoying the thunder. I got treated to several waves of lightning here, at first during the afternoon, then late evening, then the main night time event, I was filming out my bedroom window with my mobile phone and Go Pro, I succeeded in capturing this one with the latter, lashing across the sky over my house, you can see the reflection of the bolt on the window, rite after the flash there was a sudden gunshot sound which gave the impression that this bolt struck down somewhere nearby, perhaps hitting an aerial or power line. However it was when darkness fell that these storms truly came to life as the cold front moved further inland.

Numerous linear thunderstorms exploded to life during night time hours, these where storms covering miles of countryside with completely sheared back-building updraughts that kept regenerating in an endless cycle with large red and white cores on radar which seemed to last forever. These cells where pretty much sitting over towns and countryside moving at a snail's pace while dumping monsoon style rainfall constantly, once one cell eventually left the area a new cell would form behind brining more monsoon rain to the same location, this cycle continued unabated well into the night and it soon became apparent from reports on social media that this storm was an exceptional event, it was fast becoming an historic event. Once darkness fell I was out on the chase, it was now dark enough to see lightning and with such active cells forming I was sure I was going to get a good show, I knew there where sheared lines to my SW, W and E all producing sparks however because of the rain I couldn't see a thing, I drove to the top of Glenshane Pass for a better view however I was shocked when I drove into a wall of what looked like dense fog or mist, the high moisture content of this set up and moisture evaporating off the road had killed all visibility, I could barely see beyond the headlights, I knew this was incredibly dangerous, black, no road visible, heavy rain, I had a very strong feeling to stop going that direction so I trusted my instincts and went back to my house as seeing lightning from here in this rain was hopeless.

Good job I trusted this feeling as further out this road over the mountain there were major floods and landslides unfolding with some drivers unable to make it home until morning. I spent the night watching the night lightning from my bedroom, the big flashes, loud thunder and the continuous thunder of the monsoon rainfall while monitoring real time reports on social media, this storm was affecting everyone, it was the talk of facebook and twitter and as the night went on the lightning and rainfall got worse so I decided that the next day I would investigate some of the worst hit areas, I relaxed and read a book while the lights in my room flashed on and off from distant lightning crossing Antrim then finally I fell asleep with the floor below the window soaked in rain water.

The next day I headed straight out to the site near Claudy which had been all over the news and social media at day break. The bridge outside of the village had been wiped out by the storm, it looked like a huge chunk of the bridge had been bitten off by some giant monster during the night, it was absolutely shocking to witness in person. The Police had the road cordoned off, I really wanted to walk over and get stills of the damaged section and despite asking PSNI officers on site I wasn't allowed for my own safety so I took a few DSLR shots at a distance then backed off into the countryside, I decided that the drone would have the best seat in the house so the Phantom 3 Advanced became my main tool of the day.

I found a location in the countryside away from any congested areas yet only 350m from the bridge and got the drone in the air. I climbed to 100m altitude and began taking aerial stills and segments of video. Check out the flattened grass to the left and right of the river, that's where the river was the night before, pretty much level with the footpath and close to the main road itself.

Overhead view of the main Claudy bridge, altitude 70m

I hovered over the other side of the river at 52m between trees swaying in the breeze to get a better perspective of the main damage, this was staggering to view on the tablet's screen in real time.

Deep crop from the first image, two bridge arches and main central section completely gone, the force of the water combined with floating debris such as trees stripped the structure away, it's a miracle no one drove across this when it happened. Imagine driving along this road in the dead of night, torrential rainfall is hammering your car and your wipers are on full speed yet its difficult to see far in front of you, the car's headlight beams struggle to penetrate a curtain of monsoon rainfall then suddenly a flash of lightning lights up the landscape and you see that the bridge is gone and where there was once a road is now a gaping chasm filled with raging brown flood water, what a frightening thought.

I drove on down the road and by pure chance I came across another damage site not far from the main bridge which was also cordoned off by the police so I parked and hiked down for a look. I was astonished at the damage I witnessed, this was a road flanking the river which meets a bridge, however the road was completely ripped to pieces, it took me a while to get my bearings and mentally relax and actually take in the damage and visualize what must have taken place here the night before. I immediately got chatting with the locals here who recounted their experiences with the flood including a lady who got caught up in a landslide and flooded road who was stuck all though the night and who only made it home at 06.00 and despite calls no one came to her assistance, she personally witnessed 13 cars floating down a river, yet amazingly no one was in them. The older gentleman in the image was great to listen to, he recounted big storms and floods of 'yesteryear' however he admitted that despite living here all his life he had never witnessed anything like this before.

I learned that the road and fields where covered in Salmon first thing this morning. Another view of the road, the river had burst its banks and tore through the road from the direction of the grass at the top of the frame, the place was covered with rocks and boulders not to mention flattened and uprooted trees.

The drone was once again in the air which offered a superb bird's eye view of the situation. The flattened grass once more provides evidence of how this river was during the climax of the flood, clearly it would have been flowing under those trees on the far right, then on the left it covered the field and crossed the road before joining the main river again.

I felt like I was standing at the epicenter of an earthquake, the road was broken, twisted, and gaping with large holes and caverns were tarmac had been washed away exposing the foundation below, it was almost as if a bomb had gone off.

These images don't even do the scene justice, you really had to have been standing here to take it all in, I could almost feel the energy from the event still lingering here and yet again I was astonished that no one had been killed or injured here when this road was swept away, the torrent of water would have easily carried a car downstream, there would have been no time to get out if you had drove into this.

Road, trees, stone fence and farmers gate all wiped away, you can also see some of the smaller trees flattened with persons on the ground for a sense of scale. I got a call from Dad reporting dramatic flooding near Maghera back home, I still had three batteries left in the drone and plenty of daylight hours so I headed that way.

The Moyola river at burst its banks, this was one of the country roads not far from Tobermore bridge, earlier a lady had to be rescued on this very same road, even now later in the day not many wanted to risk it but some did, luckily I had the drone in the air when they did, the subject matter was very dramatic, acres of fields were flooded here. I obtained enough aerial and DSLR footage to make three separate videos which I have included below.

August 22nd historic storm event, most of the lightning was embedded inside rain and of the in-cloud variety but I captured this one with the Go Pro during the evening over my home, slowed it down for a better look, interesting crack or gun shot sound afterward. Also flood damage to road in Claudy the following day.

Drone Flight 527, August 22nd 2017 on view is the collapsed bridge which was shown by many news stations as well as another site where the road was completely washed away, tarmac stripped, boulders and rocks gone, large cavities where the road once was, trees and gates all gone, the force must have been horrific, the aerial view shows how high the water was the night before due to the affects of the flattened grass either side if the river. The destruction was impressive, sobering and frightening.

Drone Flight 526, August 23rd 2017, aftermath of historic thunderstorm and severe flooding event. This time drone footage of the fields near the Moyola River which had burst it's banks and van driving on flooded road. The white car was someone I know, permission was given to film them so I could get closer to the action.

This storm event will never be forgotten in this generation, it most certainly was the most damaging severe thunderstorm I have ever seen and it affected the lives of many people that night in one way or another, social media was full of accounts of the storm and hundreds of images of the damage it caused. Although it was not a photogenic storm it did make up for the lack of structure by shear severity, the slow moving high based back-building nature of these organized cells where the primary reason why so much damage happened, we got a months rainfall in just a few hours, the rivers and roads simply couldn't cope with the deluge, it was quite unprecedented and the aftermath is still being felt as I write this during September, I was astonished to see images taken of the Sperrins showing massive mudslides on the mountains and valleys near Plumbridge, nobody living today had ever seen the likes of that before. I'm glad I got the drone in the air to document the Claudy event so I can have a visual record of this rare damage. It wasn't that long ago that I was complaining about how poor this storm season has been, then this happened, it just goes to show how incredible and unpredictable nature can be and I wonder what else is in store over the coming Autumn and Winter months, thanks very much for reading.


Martin McKenna

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