Date: 10th July 2004   Time: 10:37 BST
Macclesfield, Cheshire UK
Path: A few miles northwest

Polar Maritime in slack flow (convergence enhanced)
Duration: ~5-10 minutes
Type: Potential Supercell - horseshoe evident
Average lightning type: None
Average discharge rate: 122 seconds (over 1 hour where rates were up and down)
Footage Quality:
VHS / Hi-8


I spotted some mesocyclonic activity to the northwest of Macclesfield in a similar location as the tornadoes of T0014 and T0027 (might be the "Cheshire Gap" effect encouraging this location!). The synoptics were similar to T0014 as well, only drier and warmer. The cloud base actually took the form of a classic supercell in rotation mode - the "horseshoe" clearance approaching from the left, and the mesocyclone hang-back just northeast of it with a rotating dangly bit under that. The "horseshoe", according to US Midwest chasing circles, is renowned for being a precursor to a tornado and is evidenced well in proper supercells.

The dangly bit (small scud funnel of sorts) is the main focus of this footage, which upon time-lapsing turned out to be rotating into the updraught. The lowered condensation point was likely caused by cooler air being sucked back into the updraught, indicative of tornadic genesis. The rotation was slow, barely visible in real-time, but as mentioned it is better evidenced in the timelapse (video above). This vortex is exactly where one would expect a tornado to emerge if vorticity was stretched enough.

However, we're dealing with the UK here. CAPE is usually weak, so this just remained a scud vortex that never wrapped into a more defined funnel or touched the ground. The vortex lasted for about 7 minutes before ascending back into the updraught.

No thunder or lightning activity was observed from my perspective, but may have been downstream. This is also common in sheared supercells not to see much lightning activity around the mesocyclone itself, let alone several miles south of it.

CHARTS (Credits)


Mark Seltzer  www.electricsky.co.uk


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