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TORNADO WATCH 2014/008

A TORRO TORNADO WATCH has been issued at 22:45GMT on Saturday 9th August 2014

Valid from/until: 03:00- 17:00GMT on Sunday 10th August 2014 for the following regions

Parts of (see map)

Much of southern, central, and eastern England, and parts of N England

Wales

Channel Islands

THREATS

Tornadoes; wind gusts to 60mph; CG lightning; hail

DISCUSSION

Deepening Atlantic storm with tropical airmass within its warm sector will cross the watch area during Sunday. Although the exact track is still somewhat uncertain, there are indications from several models that a dual-centred system will evolve. The first centre should move into Wales later tonight, with the main centre crossing SW England and heading NE to Lincs by afternoon, whilst the first centre tends to fill or is consumed by the second.

Strong lifting from a sharpening upper trough should steepen lapse rates enough for embedded convection to develop close to and to the south of both centres of low pressure, with wind shear favourable for severe weather, especially to the south and east of the second, deeper, low pressure area.

A mass of heavy rain is already moving in, and through the latter part of the night, embedded convection may affect parts of Wales and SW England, as the low pressure centre(s) move in. During Sunday morning, as the sharpening upper trough digs into the moist sector, it is possible that a squall line may develop across southern England/E Anglia. Additionally, ahead of the low pressure area moving from SW England to Lincs, convection may develop in the moist sector.

In each of these areas, low-level and deep layer wind shear appears sufficient for severe thunderstorms with strong winds and perhaps a tornado or two. The main caveat with this watch is that the maritime nature of the airmass would typically suggest fairly meagre lapse rates - however, global and mesoscale models indication fairly decent instability associated with this system (~1000J/Kg CAPE). If instability and shear can combine favourably, a strong tornado is possible.

The area from SW England to Lincs, and points south-east of there appear to have a higher risk of severe weather than elsewhere in the watch area. Please note this forecast has been issued early due to the fact the situation will not be monitored by TORRO overnight.

Forecaster: RPK

UK MAP
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