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

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)

UK Weather Chase (Sam Whitfield) footage from Plymouth
Will Woodgate's insane footage from Plymouth
Footage from StreetZips

Video of live lightning strike sferic reports from Iain Meteorscan

Student's Snapchat catches huge lightning bolt striking just metres away from him


Mark Seltzer  www.electricsky.co.uk


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