THUNDERSTORM T0106 Date: Saturday 27th May 2017
Time:
01:00 Local Location:
Exeter, Devon UK. Path: Few miles west, about 20 miles for Dartmoor cell, and
developing cells overhead
Synoptics:
Plume strongly destabilised by upper trough (low out to the
west) Duration: about 35 minutes Type: Large Multicells (MCS) sharing same Anvil Average lightning type: IC Footage Quality: Full HD
After a very warm couple of days, severe
mid-level thunderstorms broke out in response to a very strong upper trough,
with the most intense over Plymouth and Cornwall late on the 26th, then the
rest of Devon after midnight, spreading to Dorset, Wales and Somerset during
the early hours of the 27th.
The video is not time-lapsed (apart from the montage right at the
beginning). I shot this in Exeter looking west-northwest where cells weren't
quite overhead, but instead were developing all around.
I think I even struggled to see this frequency of lightning discharge in the
US, especially when watching the footage from Plymouth. Overall, this was
probably the biggest lightshow Devon has seen in years due to it's frequency
and geographical extent. Most of the lightning was high-level intra-cloud,
often in call-and-response with other towers, and the environment was
relatively dry enabling you to see the towers which are quite often obscured
in these continental plume situations. The upper-level nature of the
lightning meant that the thunder was relatively quiet and ambient, with very
low CG count.
Environmental conditions were quite unusual for this part of the world, and
severe conditions were not obvious in Met data. Less than 0.5s discharge
rates observed over Plymouth (search Youtube for footage). Multiple Sprites
were also captured in UK meteorite cameras. It all looked very good in terms
of upper-forcing (very strong cold upper trough), low level jets, and a
reasonable (but not excessive) amount of CAPE, but something else was
leading to high lightning rates. There was no Saharan dust in observations
(high cloud condensation nuclei are thought to increase lightning rates),
but the vertical wind shear was low through the column, thus perhaps
allowing for very efficient charging. Being forced linearly and dynamically
by a trough, the cells were able to continue developing strongly despite the
low vertical shear, and also "communicate" with each other, perhaps also
allowing for higher frequency of weak discharges.
CHARTS
(Credits)
