AUTUMN
2005 - PART 1:
The Atlantic switches on! October 15th-25th
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Rather unexciting weather has been
my lot since the end of June, when I had my last decent
storm to go after. This all came to an end in October,
when finally the Atlantic cyclones began to make their
presence felt. Since then there has been an excellent
mixture of thunderstorms, squalls, hail, all the stuff
that makes the weather photographer cheer up!
It's been rather busy at the moment. At the time of
writing (October 28th) we have gone "round the
clock" on the Tropical Storms/Hurricanes naming
system, with Tropical Storm Beta (they are having to use
Greek letters for the first time ever) probably to be
upgraded to a hurricane soon - the first time that 13
hurricanes have formed in one tropical storm season and
there's still a month to go before the end of the season.
Meanwhile Hurricane Wilma was the deepest one ever
recorded at an incredible 882Mb eye pressure (982Mb is a
typical central pressure for one of our cyclones). It
bombed to a Category 5 from a Tropical storm in little
more than a day! A lot of records broken, then, in a
short timespan.
So records fall everywhere and the arguing about climate
change continues. Trouble is, we have only been recording
tropical storms for about 150 years, and we've only had
reconnaissance flights and satellite imagery/data
available since the second half of the 20th Century. So
what occurred prior to all of this? We only have
fragmentary evidence. Interesting stuff, all the same...
Back to here, and on Saturday 15th, despite an almost
windless anticyclone sat over the UK, the lows were
brewing up out there in the Atlantic. The first sign of
such a happening is often the ground-swell, as any
coastal dweller knows. Ground-swells are generated way
offshore - like far travelled ripples from the
disturbance on the pond's surface, they migrate outwards
from the disturbance, barely noticeable to offshore
craft. Once they reach shallow water, however, they build
into a series of long, slow-moving tall waves - hence
their attraction to surfers.........
At Borth, they ran ashore one after another in
the still and watery sunset....
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These are over 2.5m in height.... a tricky job
using the camera handheld in low light
conditions, but luckily Borth has timber sea
defences which have useful flat areas for sitting
a camera for longer exposures....
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...which create some weird but pleasing effects!
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My first storm-intercept since late June was on
the afternoon of October 19th, again at Borth as
the radar indicated a group of heavy cells
heading NE across the Bay. This was the best,
giving a number of good C-G lightning flashes and
booming thunder as it headed for the coast north
of Tywyn....
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...with a developing weak gust-front ahead of the
advancing precipitation, here seen sideways-on...
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...plus of course a large, fluffy Cumulonimbus
anvil...
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Great
thing about Borth is the way the wet sand
reflects the sky...
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Especially as the sun starts to set!
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Here's a
quick diversion before going on to the next
sequence of events. This, taken on Saturday 22nd,
shows instability being released in the lower
levels of the atmosphere, resulting in thin,
towering cumulus clouds. However they're only
going up so far before spreading out downwind
(wind being R-L). This suggests two things at
work- firstly a mid-level inversion (or cap)
stopping them from going up any further and
secondly a layer aloft in which stronger winds
exist (it's pretty usual to see windspeed
increase with height). Thus they're bubbling up,
meeting the cap, and spreading out downwind from
that.
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The following
week started with weather warnings issued for
many areas for heavy rain and ended with the
warmest October 27th since records began in the
bag! Monday 24th saw a substantial low-pressure
system anchored to our NW and a trailing front
reaching way down towards the Tropics, with a
moisture-laden warm S to SW airflow being set up
over the UK (the so-called Warm Conveyor). In
such setups, as the air comes in off the sea and
is forced up over the mountains, often
drastically enhanced rainfall results (the
technical term is orographic enhancement). The
result is enormous amounts of water flowing down
the mountain catchments and causing flooding
along the major river valleys.....
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On the morning of the 24th
flood warnings were out for four rivers in Wales
including the Dyfi here and the Mawddach/Wnion
further north. It was difficult to get a decent
shot of the Dyfi (above) in flood (pouring rain
didn't help!) so I headed northwards, into Coed y
Brenin, where the Mawddach flows...
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This is at the top of Rhaidr Mawddach - where the
river drops several tens of feet over an
intrusive igneous sill consisting of the hard
rock, microtonalite - you couldn't safely get to
the bottom of the falls as that area was
underwater! For scale, the river here is 25ft+
across!
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There are two waterfalls of note here, one on the
Mawddach and one on its major tributory, Afon
Gain, with the remains of the old Gwynfynydd gold
mill in between. The rivers join below the ruined
mill. Pistyll Gain is a bigger fall than Rhaidr
Mawddach: in this image it is seen from the main
footpath, but I decided to get a little
closer....
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...but this is as close as was safe. A slip into
the river below would have spelled the immediate
end of me, so in clouds of swirling spray I
stopped here and attempted a few shots, having to
dry out the lens in between. This is the best of
them! The noise was literally thunderous! A great
morning out in rough conditions!
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The following day, Tuesday 25th, had for some
time been expected to deliver some thunderstorms
in the unstable post-frontal airmass. A pore over
the charts the night before led rapidly to the
conclusion that an early start would be essential
for anyone wanting to see much in this part of
Wales, so I was off to bed early that evening. I
rose at 0400, drank black coffee, checked all the
forecast data, checked the camera really had
dried out properly, confirmed on rainfall
radar/infrared satellite/lightning plotters that
something was indeed heading this way, drank more
black coffee and so on. The plan was to keep
observing online then head down to Borth at 0700,
when signs of daybreak ought to become apparent.
At just after 0600 I caught a flash in the corner
of my eye through a side window and moments later
a boom of thunder rolled through the valley.
Hastily powering down the computer whilst
simultaneously yanking the modem cable from the
phone socket, I sat there feeling very alone all
of a sudden - minus my data-feed on the screen,
my fix that could make an intercept a success or
failure. But what the hell? - the surface charts,
satellite and radar all showed thunderstorm cells
scattered along an active surface trough
coincident with an upper shortwave - why not just
get out there and go and see!
Leaving Machynlleth sometime before 0700 I made
it a few miles down the valley before running
into a deluge of Biblical proportions forcing a
slowing to 10mph and peering into the rain and
spray to see where I was heading. Occasional loud
crackles on the radio coincided with stabbing
lightning over the hills on the north side of the
valley, while ahead a most unlikely thing
appeared for the time of day - a traffic-jam.
Glandyfi has one of the most beautiful views in
Wales, looking across the Dyfi Estuary to the
wooden railway bridge and the hills beyond, but
also has one of the narrowest bendiest bits of
any A-road in Wales. Here, large vehicles meeting
often have to engage in tricky maneouveres in
order to pass one another, and this was indeed
the case now. We sat there as the rain turned
heavier, then to hail, while odd flashes through
the gloom were probably lightning but could have
been anything in that level of visibility!
Finally on the move, I negotiated roads awash
from the downpour, to arrive on the sea-front at
Borth at about 0730....
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This is what you get by trying to photograph
storm-clouds moving at 60mph before it has gotten
light properly! This is a 20-second plus
exposure. The brighter area is not due to
lightning but to a small gap in the clouds i.e. a
lighter area, blurred by the speed of the clouds'
movement. I quite like the effect!
With one huge towering storm to my east - where
the sun rises - daylight would be late arriving
today.....
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By 0800 it was attempting to brighten a little
and I could see that I was sat under a
"shower-train" updraught area. By
which, I mean that convection was going on
overhead and was maturing (i.e. giving downpours)
downwind and a little to my NE. Given that TORRO
had a Tornado Watch out on parts of the western
UK, it seemed worth staying put and scanning in
case any spin-ups occurred in this cloud-bank,
but none were forthcoming. Had they done I had
travel options both N and S (storms moving SW-NE)
so a sharp exit would have been easy if required.
The photo above was taken at around 0830 looking
out northwards to clearer skies.
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The
updraught base moved away NE and left a rather
unexciting greyness in its wake. I was just about
to decide to head home for breakfast when a small
clearance in the grey stratus revealed much more
to come, with towering cumulus and cumulonimbus
strung along the horizon. I stayed put again.
These cells duly arrived but were of little
photogenic value as they approached. An evil dark
grey wall of rain with occasional lightning
flashes was the lot. But through a gap between
cells and their rain I could see that conditions
beyond were much clearer. This suggested finding
a venue where the view downwind was unobscured by
buildings etc - storms can look more amazing as
they clear an area sometimes - so I headed off to
Ynyslas sands, where there is an open view
straight up the estuary, and waited...
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First the clearance passed Aberdyfi, with a large
anvil visible overhead....
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Then the sun, still low in the East, started to
back-light the flanking towers of the storm as
they billowed up. I could have done with a 20mm
lens here - it would have caught the whole thing
nicely!
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As the whole lot rolled on up the valley
conditions began to brighten at ground level...
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Retreating quickly away now, this is the last of
the shots. Nothing that severe about these
storms, I thought to myself, but it had been
great to get out there on a madcap adventure -
with an early start more reminiscent of an Alpine
climb!
Getting back to Machynlleth around 1000, I was
greeted by two fire-engines heading up out of my
street. The same cell had caused quite a bad
flash-flood, requiring some hasty pumping-out
work. Fortunately my place was unaffected. A look
on the rainfall radar (below) indicates that with
rainfall rates of >46mm/hour (lower red area),
this was a cell more than capable of causing
local problems with flooding.
2 lots of
storms in a week - and lots else in between - now
that makes a change! With the remains of
Hurricane Wilma affecting us this weekend, I
wonder what more we can expect??
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