SUMMER
2004 - PART 4:
Spectacular August thunderstorms over Cardigan Bay (plus
a brief note about hurricanes)....
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The thundery August continued apace
after my experiences on the 12th, with a slow-moving
complex low-pressure system in residence over the UK.
This August has been an incredibly wet one, with more
thunder days than I remember in a single month. Some of
the rainfall has been exceptionally severe, as witnessed
by the poor people of Boscastle in N Cornwall. Why?
These low-pressure systems have either had a strong
southerly inflow into them, or have absorbed remnants of
tropical storms and/or hurricanes. Either way, they have,
because of this, become especially rich in warm, moist
air. When such air moves north into cooler climatic zones
(e.g. NW Europe) it can no longer hang on to the moisture
which basically means that when it rains, it really
chucks it down! So it's worth watching out for hurricanes
in their dying phase. Click HERE to find
out more about how ex-hurricanes can influence our
weather!
The 16th will go down as a date to remember for
the people of North Cornwall. Here we had the
fortune to miss out. I photographed this
"messy" looking storm at Borth in the
evening.....
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....trying some telephoto shots of the sunlit
waters and the rumbling blackness beyond. Sort of
works!
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On the 18th a more impressive band of
thunderstorms moved up across Wales. Here's one
of the first, once again seen from Borth, with a
mean-looking core of torrential rain......
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....with a real beastie working up from south of
Aberystwyth. The anvil towers over the blackness
beyond, its edges visible L and just about
visible R. I waited until this got close, with
sadly no better opportunities to get images. Too
many other clouds in the way! The storm followed
me back up the Dyfi valley to Machynlleth, where
torrential rain and loud thunder lasted for a
while. Some of the C-G lightning strikes were too
close for comfort!
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After it passed I drove northwards to Tywyn and
beyond, stopping to photograph a half-hearted
display of mammatus clouds from the bridge over
Afon Dysinni. Just having gone "click",
a 5lb sewin leapt from the inky waters into
mid-air in my field of view! A second or two
later and I'd have had a pic worth posting here!
Looking inland greyness and low light - but to
the coast brighter skies beckoned. North to my
usual vantage point near Llwyngwiril and a mass
of Cbs were visible, moving gradually up Cardigan
Bay. Tywyn looked to be the place for an
intercept..... |
...where vigorously building convection had
established itself in a NE-SW line parallel to
the coast. New towers shooting up on the landward
side of already mature thunderstorm cells whose
anvils form the backdrop...
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....this
is for reference purposes a shot of a
scud-funnel, under the cloudbase somewhat L of
the field of view in the last image. These are
not funnel clouds. They are bits of scud (tatty
clouds that run along under the main cloudbase
but are not attached to it). Sometimes, at a
glance, they can resemble funnels, which is why
binoculars are useful for checking such things
when they are distant.
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The truly mountainous clouds continued to grow -
and in no time more torrential rain begins to
fall from their bases. Note the faint line of
paler clouds at the main cloudbase: now what
happens next?? |
This is what
happened next! Cooled air dragged down by the
rain pushed under and lifted warm moist air in a
line parallel to the storm. The warm moist air
then condensed out its moisture into a long
straight, ominous-looking cloudbank, known
technically as Arcus but generally as a
roll-cloud. In this image the downdraft can
actually be seen - it is making the rain shafts
slant down and L. The roll-cloud thus marks the
boundary between the outflow - the cooled air
gusting down with the storm's downdraught - and
the ambient surrounding air. Roll-clouds that are
this well developed are unusual in the UK.
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The
roll-cloud rather lost its good definition
shortly after as heavy rain and booming thunder
once again took over. I headed back south along
the coast, where at Aberdyfi a distant
thunderhead was nicely framed by two nearer ones!
This was the last decent break in the clouds that
I was to see on this day.
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On the way back to Machynlleth, there was much
evidence of low-level moisture condensing in the
cooled outflow air and forming banks of foggy low
cloud over the Dyfi Valley....
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...and
finally a jump ahead by a few days to better
weather and an incredible crop of hawthorn
berries. In August!!! Will this mean a hard
winter 2004-5? Ask me in December!
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