THUNDERSTORM T0014 Date: 15-06-1998
Time: 15:25 BST Location:
Macclesfield, Cheshire UK Path: Core: Overhead, Meso: 3-4 miles NW, moving southwards
Synoptics: Convergence in cold
unstable northerly flow post-depression Duration: ~1 hour Type: Small Supercell Average lightning type: C-C Average discharge rate: n/a (C-Cs not captured)
Footage Quality: VHS
first supercell-like thunderstorm, and much to my surprise, in the UK
outside my house (cheap chase)! With this season being fairly active, this
was the icing on the cake. Originally I wasn't on the lookout for storms on
this day as there weren't any forecast for the north (mainly for southeast
England) and I was at school (I was 14).
after a previous cell that passed through at around 13:30. We were doing PE
and it absolutely tipped it down, so we did alternative PE by watching
England beat Tunisia in the World Cup group stages in the gym. I remember
some pupils protested against this and played netball in a monsoon.
Anyway... this first cell had ominous characteristics that deferred away
from common British thunderstorms, such as a dark browny-coloured rolling
base (likely Arcus) and a tremendous downpour, but little lightning
activity, so it may have been capped at or below -20C (frontal layers?). Low
bases and no sunshine were the feature of this day. It cleared at 14:15,
leading the way for this mini Supercell at around 3pm.
I was returning home
in the torrential rain from the core of this cell as it passed over with
weak C-C lightning cracking overhead.
By the time I got the camera set up (dripping wet) the lightning activity
had dissipated and it fell silent. However the lightning wasn't of any
relevance after I found something else to film... albeit I didn't
notice at first.
I set the camera up facing northwest down the Cheshire
plain, not really taking any notice of the storm at first as I was still
trying to dry myself off, and hoping to catch some electrical activity. It
turns out I pointed the camera at a mesocyclone, as the clouds were
rotating, and a funnel was already trying to form, but I didn't notice it at
first due to the low-contrast backdrop and faffing with clothing. I only
noticed, and frantically rustled the camera, when I finally saw a piece of
cloud lowering against a thin sliver of brighter skies. It turned out to be
a silhouette of a rotating vortex about 3-4 miles away northwest with a
low-contrast funnel connecting it to the parent mesocyclone. It was brief
and disappeared quickly, but analysing the footage in the following years
has made me more and more convinced this is was a brief tornado despite
In the footage (top of page), the parent funnel was very difficult
to see against the same-shade background and poor-quality VHS resolution,
but messing about with the contrast shows something is there.
Why the big deal? It may have been brief, tiny and barely visible, but it's
a big deal because it's the UK. Confirmed tornadoes in the UK are extremely
rare and that's what makes this case interesting and worth spending a bit of
time analysing. I have had this
footage on Youtube for over a decade, and there has been much debate as to
whether or not this was a tornado, a funnel cloud, or just scud, often with
the usual amount of unhelpful trolling from over the water. I have since
deleted that video and uploaded the above improved version.
is summarised below.
Very low LCL (storm base), so this must have only been
a few tens of feet above the ground at the most, and does appear to be
extended to the horizon for a few seconds. Touchdown likely considering the camera is looking
down a plain (150m elevation looking down to ~75-100m - i.e. a reasonably
flat if not slightly negative angle)
Tornado Support: Evidence of focussed turbulent rotation in
the lowering cloud
Tornado Support: Rotation evident in
timelapses of parent cloud and convective towers
Support: Background cloud is
the underside of an Arcus/"Whale's Mouth" - indicating "horseshoe" outflow present (common
precursor to tornado)
The positioning of the core (overhead), mesocyclone (ahead) and horseshoe
Arcus (behind behind) in relation to the storm movement (southward) reflect
the structural characteristics of a classic tornado-ready supercell.
Support: Lightning was within
the core, which moved south with the rain, leaving the back-building
updraught lagging behind - classic supercell characteristics
So after the
dissipated 20 seconds after I spotted it, I was left viewing the slowly
rotating mesocyclone and towers as they span towards the south. Every now
and then little scud funnels would appear under the mesocyclone, but none of
them developed as fully as the first.
This gradual clearance gave way to a clearer view of
the rear of the sloping arcus cloud to the northwest.
As the cloud broke up,
substantial tower growth was visible over the Pennines to the northeast from
developing storms. The anvils were showing mushroomed characteristics with
no fibrous features (I have only Mk1 eyeball footage of this) which indicate
strong CAPE and moist throughout depth, and perhaps some high-level
stability preventing full ascent into the cold tropopause.
The heavy rain during the day from the two cells at
13:30 and 15:00 caused minor flood damage in Macclesfield and neighbouring
Prestbury where a severe downpour was also reported on the BBC news.
Tytherington High School just down the road had to get a fire-engine to pump
the water out of the music and reprographics rooms, and the River Bollin
that runs through Macclesfield had suddenly rose 80cm-100cm in places. The
water levels were clearly marked by flattened grass on the riverbank the
following day after the flooding had receded, and part of the footpath on
the Beach Lane bridge that runs over the Bollin had collapsed in a landslide
(see images below).
The only data I have to go off is
are the below satellite images. It is clear that a convergent front aligned
itself along the spine of the country, likely a higher wet-bulb plume than
to the air further west. The atmosphere was cold with a likely maximum
temperature of 14-15C, reflecting an unstable northerly on the west side of
a low. Judging by the satellite imagery alone, the upper pattern likely had a decent strip
of shear vorticity marking the line of convergence down the spine of the country
(ascent), with clear skies and suppressed cloud immediately to the west
(descent). The polar jet is likely over Barcelona and across Central Europe.
The shear vorticity strip, combined with a moist low-level plume would give
rise to the instability and low bases observed here, and the likely
convergence would help with vertical shear and low level vorticity, moreso
than any CAPE values themselves which were probably rather low compared to
what one would expect for a classic (US-style) supercell.
If anyone can provide more broadscale
weather data from this day, please contact me.