THUNDERSTORM T0027 Date: Thursday 5th August 1999 Time: 14:08
BST (Supercell) Location:
Macclesfield, Cheshire UK Path: Multicell: Overhead / Supercell: 5-8 miles Northwest
Deep upper trough overriding surface cold front with RP
Maritime behind. Slack gradient wind. Duration: 40 minutes (Multicell) Type: Linear Multicell & Supercell Average lightning type: C-C (Multicell) Average discharge rate: 105 seconds(Multicell)
Footage Quality: VHS
14:08 - T0027 Part 1 - Electrified Multicell on Cold Front An elongated
occlusion had passed northwards during the morning, leaving behind a
returning polar airmass but with a pronounced upper trough (driving the
fronts) hanging over Macclesfield.
A line of convection, aided by surface heating, looked like it formed along
the axis of the upper trough. This allowed for this fairly active
electrified thunderstorm. A linear tail of torrential rain swept up from the
West Midlands across Macclesfield giving a few C-Cs and distant C-Gs with
The cell that passed
over Macclesfield gave some low-amp C-C overhead and C-G over the
Pennines in the distance to the east. It cleared up allowing a view of a
frontal anvil overhang spanning the entire northern sky. Following this, a few non-thundery showers (with weak anvils)
developed to the southwest and passed overhead, giving further torrential
clear there was cold advection as a timelapse of these follow-up cells showed
the boundary layer wind was westerly, but mid-level was southwesterly, and
high level was still south to southeasterly. This is important to note for
the wind shear environment during what was to follow a couple
of hours later...
16:30 - Developing Supercell with mesocyclone and Gustnado/Tornado event I decided to tie this in with the T0027 cluster, even though it occurred a few hours
later separately, mainly because I didn't observe any lightning activity.
What I did observe was what appeared to be a mesocyclone, with a very low
base, uncharacteristic to the rest of the day's convection.
It was positioned to the northwest of Macclesfield at 16:30 perhaps 5-8
miles away, and the clouds around it were moving in all
directions at all heights. From what I can gather looking back at the
footage, there was a low-level northerly, a mid-level southwesterly, and
upper level southeasterly. There could have been lucky convergence with the
either outflow boundaries from other showers, or from the surface low
itself. A NOAA 850hPa wind analysis below shows actually, through the axis
of the trough, there was likely a wind minimum with a maximum either side of
it. It is likely that this formed right in the heart of the trough, allowing
high low-level CAPE and mesoscale wind boundaries (such as outflow from
prior storm) to converge together.
Whatever the environmental conditions, it was enough to produce
convection with what looked like a classic supercell base. A rapidly rising
(to the naked eye) updraught was evident on the right hand side of the
mesocyclone, so I focussed the camera initially on that. It was obvious
there was either horizontal shear through convergence as the mesocyclone
appeared to be rotating, especially in time-lapsed footage.
Low cloud close to Macclesfield was moving in a southerly direction while
the mesocyclone drifted northeastwards. What looked like a roll-cloud with swirls
was seen in the
local skies, supporting large wind shear. As I watched the mesocyclone twist
in the distance, with my camera trained on
it, the updraught on the right hand side went completely vertical and I saw
cloud start to form under it all the way to (from?) the surface. This was in
a similar position as the tornado spawned from T0014 the previous year 1998,
though being on the flat Cheshire plain I doubt locality had anything to do
with this coincidence.
The ragged cloud seem to tighten into a funnel-shape and twisted for a
minute or so. Then, a SECOND swirl of condensation developed to the right of the primary, this time starting
from the ground up and appeared to be a bit closer than the first. It was
clearly on the deck given I was looking down a plain, so I deem this either
a well-defined Gustnado or Tornado. Characteristics of both types were
evident. I zoomed
in with the camera and could see pronounced and multiple sub-vortices to the
surface as it spun around. The primary funnel at this time was still just
about visible but started to dissipate.
About 6 minutes after the second 'nado, both funnels ascended into the
base. By this time the mesocyclone was moving behind trees and further
northeast. A few further local showers followed overhead as the structure of the
suspected supercell started to become more evident, demonstrating a very
dark base with arcus clouds (similar to T0014 and suggesting outflow was
present) and also an irregular mushroomed anvil. Interestingly, no thunder was heard during this whole event;
perhaps too far away or not mature enough.
Tornadoes or Funnels Argument
Like T0014, I have had a video of this event online for public
witness for over a decade (before remastering it in 2020
here). There was, in
comments, much debate about whether these were tornadoes or
funnels (no mention of Gustnadoes), mostly stating a funnel becomes a tornado when you
see it lifting debris, which is not necessarily true. In the case of these "funnels", viewing sufficient debris lifted
from unpopulated pasteurised land at a few miles distance would be
challenging! The footage clearly shows the primary and secondary
condensation funnels connecting all the way to the surface, with me looking
down a plain from higher altitude, and were rotating. If you were to
stand directly underneath them I would be surprised if your hairstyle didn't
summary I think a very rare event for the UK has been documented here. Twin
tornadoes/gustnadoes, in the UK, without having to even chase them...
(bedroom window!) what are the odds?! Has a multi-vortex ever been
documented in the UK? Am I the first? I would welcome anyone's thoughts on
this for discussion. As a time-served meteorologist, I am still a little
perplexed as to what I witnessed on this day.