Date: 19-06-2005
Time: approx 18:00 BST
Macclesfield, Cheshire UK
Type: Multicell Squall Line
Documented by: Mark Seltzer
Equipment: My Eyes

Storm Statistics: T0055.doc
Event Timeline: T0055events.xls

This event was one of the most aggressive thunderstorm squall-lines the Northwest region has seen in years, and an excellent example of when all the right ingredients come together in the atmosphere for thunderstorm development. Unfortunately I missed it by an hour or two as I was driving towards them from the south after being down in Reading University for the week. I already knew the potential for a severe thunderstorm outbreak was likely as I’d been following the forecast all week, but I didn’t get back to Macclesfield in time for the action. However the cumulonimbus towers reached such heights I could see them from Reading as I set off somewhat 170 miles away. They were enormous and were developing explosively. 

Weather situation
The general consensus suggested all the right atmospheric ingredients came together on this day to trigger these severe thunderstorms. The fuel was there with high wet-bulb potential temperature values (WBPT) existing over England by advection from the neighbouring continent. A cool short-wave trough ahead of an approaching Atlantic cold-front provided upper-level forcing and enhanced instability from aloft, whilst a slight inversion existed from the influence of a ridge to cap some of energy to lower levels. Instability and CAPE (Convective Available Potential Energy) values were therefore pretty good across central England (air mixture was correct). All that was required was some lift (to spark it all off) in the form of convergence or other low-level forcing.

Looking at the sequence of satellite images for the day, it is evident that the thunderstorms were organised in line, so convergence was probably the trigger mechanism. However large cumulus were already forming in the North Midlands and Yorkshire areas (where the shortwave trough was), as the daytime heating started hurtling towards the 30s, showing that radiative (sensible) heating alone was enough to start the process. However later, as the satellite imagery shows, the cap-breaking convection started forming along the run-up to the Welsh mountains and also the Pennines, with further development in the lee of both. This suggests a final push factor associated with orographic enhancement combined with orographic convergence. So overall it was very complicated picture, probably quite difficult to forecast.

What I witnessed
By the time I had driven closer to the development, now lying in a line across much of the North Midlands and Yorkshire, the cloud base was visible and very ominous-looking with deformed stratus rolls and very dark rain curtains. As I approached Congleton it wasn’t raining a great deal however the roads were completely flooded with fountains of water spewing out of the drains, so the storm must have just gone through as I arrived. Distant thunders were still rumbling away to the east with the odd distant flash of sheet lightning occurring. By the time I got back to Macclesfield the storm was long gone and only a few distant rumbles were heard from the east.

Accounts of the ferocity of the storm system were soon spoken on the news with power outages, widespread flooding, golf ball hail and even a few lightning injuries from tremendous intensities of C-G. These intensities were reflected in Wetterzentrale’s lightning “sferics” charts at the time (C-G strikes detection).

APPEAL: If anyone has any footage, photos or eyewitness accounts of these storms to share on this page (credited to yourselves of course) I would be more than happy to display them.

Links relating to this thunderstorm outbreak:

VISIBLE 19.06.2005 15:31

VISIBLE 19.06.2005 15:31 + Grid
INFRARED 19.06.2005 15:31
INFRARED 19.06.2005 15:31 + Grid
COLOUR 19.06.2005 15:31
COLOUR 19.06.2005 15:31 + Grid