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Storm Forecast
Valid: Fri 09 May 2014 06:00 to Sat 10 May 2014 06:00 UTC
Issued: Thu 08 May 2014 20:31
Forecaster: TUSCHY
A level 1 was issued for the Netherlands and NW Germany mainly for an isolated large hail and tornado risk.
SYNOPSIS
A Rossby wave over the N-Atlantic streaks NW-Europe. Attendant polar front jet along its eastern fringe steers numerous mid-layer waves over N-Europe from west to east. A pronounced wave is forecast to evolve over the British Isles with a rapid motion towards Germany and Poland until the end of the forecast. Despite a weakening trend of the mid/upper jets, winds at 500 hPa still exceed 40 m/s while passing over NE France. Models offer consistent timing of that wave but its amplitude and final location remain a bit uncertain with ECMWF prefering a smaller amplitude (displaced a bit to the north) compared to GFS.
A large-scale upper low over SE Europe won't move a lot throughout the forecast, so unsettled conditions persist over Romania, Bulgaria, Greece and Turkey. Rising mid-level heights bring quiet conditions to the Iberian Peninsula (excluding orographically induced convection).
... The Netherlands and NW-Germany ...
Early initiation is forecast...probably as early as 9-10 UTC. Either BL dewpoints in excess of 10 °C or lowering 500 hPa temperatures over the Netherlands support the idea of weakly capped 200-600 J/kg MLCAPE. From noon onwards, additional insolation and approaching strong synoptic forcing result in more widespread initiation and stronger thunderstorms over the Netherlands and NW Germany. DLS oscillates around 15 m/s, so updrafts could gain some temporal organization and a few longer-lived thunderstorms are possible. An isolated large hail and strong wind gust event is expected. The main focus however will be the evolution of the low-tropospheric wind field. LL shear increases during the afternoon/evening hours, so an overlap of increasing LL shear and slowly decreasing CAPE could yield an isolated tornado risk . Thunderstorms decay rapidly after sunset as a stable nocturnal BL evolves.
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