On the day in question, major convective activity
was not forecast. The high-resolution radar
(above) showed a scattering of modest convective
showers across the UK. The red arrow points to
Cardigan. This radar is available by subscription
from www.net-weather.co.uk and I can
recommend it at less than twenty quid a year for
the basic package (which includes a very useful
zoom-in tool). The other packages include a lot
of useful forecasting data. The radar updates
every 15 minutes which with the zoom tool gives
you a very good look at what's developing!
Under such conditions one
might not expect tornadoes, but they can in fact
occur with any type of convective cloud if the
right conditions are prevailing. Big, damaging
tornadoes, however, are associated with the
strong convective updraughts of the type
associated with much heavier storms.
The charts for that day showed high pressure over
Europe ridging west with low pressure in the N
Atlantic and also to our SW. A moderate westerly
airflow covered Wales. It was clear at the coast,
as seen in the above image, taken looking away
from the convection, towards the Teifi Estuary,
Gwbert and Cardigan Island, which implies that
local sea-breezes had set in. The clear air's a
dead giveaway for this. In this area the
coastline runs NE-SW, which means that a breeze
coming in from the sea would be from the NW. This
would have caused convergence of air inland (the
prevailing westerly plus the NW sea-breeze). Such
conditions are supportive of convection and the
attendant wind-shear (wind changing direction
with height - i.e. NW at surface, W 1000ft up)
would have been favourable to the occurrence of
localised rotating updraughts which can spawn
funnel-clouds and tornadoes, even if the
updraughts are weak and the resultant tornadoes
This sets the scene for Rosemary's sighting. I
have zoomed right in for the subsequent images.
Here, a small funnel-cloud is visible between the
two houses. It is protruding from a dark
rain-free cloudbase, although rain (and reported
hail) can be seen falling further to the left.
An important point if you are looking for
tornadoes is illustrated here. If you have
located a convective shower or storm, concentrate
on the rain-free part of the cloudbase. This
marks the updraught region of the convective cell
and is where any funnels are likely to develop if
the conditions are favourable.
A funnel-cloud is formed because the air quickly
being drawn into a rotating updraught from its
surroundings experiences a sudden fall in
pressure and temperature. The moisture it
contains then condenses as a result, forming
Zoomed-in, we can already see that the vortex has
in fact extended down and is close to or on the
Now, the whole funnel has thickened which in
basic terms can be taken as a sign that it has
strengthened a little. It would have probably
been causing localised gusty winds on the ground
by now, but as it's a weak tornado it is unlikely
that any noteworthy damage would have
Here it appears to have lifted off the ground
Weakening a little, its lower part is now a
little thicker than its middle section...
again - this all happens rapidly in many such
Now in its death-throes, it has taken on a
decidedly convoluted appearance...
A major loop
has now formed in the funnel....
Here the loop
has moved around - twisting with the twister if
you like - giving it the appearance of a knotted
Here the top of the funnel
seems to be disengaging with the parent cloud.
It'll all be over soon....
Starting to dissipate....
Cloud breaking up....
And gone, except for a trail of fragmented
scud-cloud, which outside of the rotating
updraught environment will now evaporate again.
Rosemary and her husband then got into their car
and headed for a better vantage point. They were
rewarded with a second unusual lowering of cloud,
which can be seen in the centre of this image.
Hail is falling to the left.
Here it is seen closer-up. It was rotating again,
but does not have the neat, ordered appearance of
the earlier sighting. A lot of fragmented
scud-cloud is forming and been drawn up into the
low cloudbase-lowering - probably a ragged
condensation-funnel. There appears to be a small
piece of airborne debris associated with the
An apparent smooth funnel has formed in this
image (LHS of lowering)....
This whole area of the cloudbase has upward and
probably rotating air-currents....
Close-up again - the funnel-like feature is still
present on the L...
In this final shot the whole mass is retreating
gradually into the distance.
Although not newsworthy in the sense that the
Birmingham tornado of July 28th 2005 was, this is
still an interesting and illuminating series of
images. The principles of tornado formation are
the same here as in the Birmingham disaster: in
this case the updraught was weak, being
associated with a weak convective shower, and
thus the tornado that it produced was weak and
short-lived: in the case of Birmingham, a very
powerful rotating updraught associated with a
violent thunderstorm produced a strong tornado
with a damaging track of several miles and a
longer still track as a funnel-cloud.
Events like the Birmingham tornado are thankfully
uncommon in the UK and can be many years between
in occurrence. Less powerful but damaging ones
happen every year in a variety of weather setups.
They can occur at any time of year and the number
we experience has increased in recent years. Some
say that this is due to climate change but there
is another reason too. There are far more people
interested in the weather these days - it's in
the news all the time after all. There are also
many more people able to capture events such as
this due to the proliferation of digital and
mobile phone cameras. Even so, many more must go
missed, especially in sparsely-populated regions.
TORRO - the Tornado and Storm Research
Organisation - both forecasts and records
tornadoes. Its staff and members visit the sites
of tornado damage and use a number of methods to
classify tornadoes on a scale of 0 to 10. The
Birmingham tornado was a T4-5, while the above
example was probably T0 in intensity, with winds
of 39-54 mph. Thankfully, a T10 (an astounding
and terrifying 270-299 mph) would be an
exceptionally rare event, as it would have the
power to obliterate everything in its path.
If you are interested in finding out more about
TORRO, visit its website at www.torro.org.uk.
Anybody interested in joining the organisation
can find out more by emailing email@example.com.
We have an active online members' Forum where all
aspects of severe weather, its forecasting, its
aftermath and its photography are discussed. The
membership ranges from people new to the subject
to professional weather forecasters and a great
deal of knowledge is exchanged on a daily basis.
Thanks again to Leona Ralph and Rosemary Brabrook
for their contributions.
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