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Possible Stormy Spell 13th to 19th Nov

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Author Topic: Possible Stormy Spell 13th to 19th Nov  (Read 3443 times)
martinastro
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« on: November 11, 2009, 09:14:08 pm »



Storm Forecast
Valid: Thu 12 Nov 2009 06:00 to Fri 13 Nov 2009 06:00 UTC
Issued: Wed 11 Nov 2009 20:17
Forecaster: GATZEN
A level 1 was issued for portions of England and Wales mainly for severe wind gusts and for a lower extend for tornadoes.

SYNOPSIS

A broad trough over Europe moves north-eastward, while warm air advection sets in over western Europe ahead of an Atlantic trough. This is associated with a strong mid-level jet streak spreading into western Europe. At lower level, a strong jet will advect moist air across the Bay of Biscay and the British Isles late in the period. Further east, most of Europe is dominated by dry air masses. Over the Turkey region, rather moist low-level air mass is present in the range of the trough.

DISCUSSION

Portions of England and Wales

Models agree on the development of a strong mid-level jet streak spreading into the northern Bay of Biscay in the evening hours, and strong QG forcing will be present in the warm air advection regime ahead of the surface cold front of low pressure over the Atlantic Ocean. A 25 m/s low-level jet is forecast by latest numerical models leading to strong low-level vertical wind shear, while the low-level mixing ration may reach more than 8 g/kg in the south-western portions of the British Isles. Weak instability is forecast due to differential warm air advection in an air mass characterized by nearly moist-neutral lapse rates. Together with strong linear forcing along the cold front, a shallow line of convection is forecast to develop in the evening hours. North of the mid-level jet, deeper convection will likely evolve cold pools due to melting of graupel and snow, helping the convection to organize. Bowing elements are expected, associated with severe wind gusts and possibly tornadoes in the range of embedded mesocyclones. The convective line will rapidly spread into the North Sea late in the period, where the potential of deep convection decreases due to weaker low-level moisture.
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