Storm Forecast
Valid: Fri 17 Nov 2006 06:00 to Sat 18 Nov 2006 06:00 UTC
Issued: Thu 16 Nov 2006 22:24
Forecaster: TUSCHY

SYNOPSIS

An omega pattern continues to affect Europe with an intense upper-level longwave trough situated over western Europe and another one over eastern Europe. Strong WAA in - between supports persistent and unseasonably warm temperatures for most parts of Switzerland , Austria , Poland and Germany.


DISCUSSION

....CNTRL / SE United Kingdom...

Multiple chances for isolated - scattered thunderstorm development will exist over most parts of S and CNTRL United Kingdom.
First round of isolated - possibly scattered convection development can be expected during the morning hours, when an upper-level trough axis will rapidly cross the area from the SW and an approaching left exit region of an upper-level jet should support an increase in upper-level divergence over the area of interest.
Broad sector of marginal instability release will develop over most parts of United Kingdom.
LL shear will be very strong and DLS is forecast to increase from the SW, so any developing storms will have the chance to produce severe wind gusts and marginal hail.
A sector of 150-200 J/kg SRH 0-1km values and increasing LL lapse rates also overlapping the low-end instability field would be favorable for storm rotation and hence an enhanced tornado threat, especially over W-UK


Next focus for isolated thunderstorm development should evolve during the 15-19Z time frame over SE United Kingdom.
An slowly eastward moving cold front will undergo some intensification due to an reinforeced temperature gradient. About 30m/s DLS will be present and there would exist an enhanced risk for a few severe wind gusts with each shower / thunderstorm. There exists a threat for an isolated tornado development, too due to the combination of about 200 J/kg SRH0-3km and low LCLs.
Weak lapse rates and only marginal veering should limit the tornado threat, but area has to be monitored if more backing can be realized than currently expected.
The level 1 over SE UK was issued mainly due to an enhanced severe wind gust threat along the eastward moving cold front.

Extreme NW France was also included into the level-1 due to a severe wind gusts / isolated tornado risk. Conditions will be similar to those described above.

...Ireland and W-United Kingdom...

A very cold mid-level airmass will be advected over Ireland during the evening hours associated with an SE-ward shifting upper-level trough axis. Widespread instability release was calculated by the latest model outputs. Shear will be significantly enhanced at lower levels and there exists a threat for a few severe wind gusts / isolated tornado reports.
Main uncertainty will be a pool of warmer air at 700hPa, which should cross the area of interest from the WNW during the 00-06Z time frame. This could have an huge impact on storm coverage.
An update for this region may become necessary later on.

...Parts of the NW Mediterranean...

Broad upper-level trough is forecast to reach SW France during the morning hours , moving towards the NE . A cool-down of the mid-levels should support up to 500-700 J/kg SBCAPE in a weakly shared environment. Scattered thunderstorms will develop, but only an isolated severe wind gust risk can be expected.

...S/SW Norway...

N-ward shifting trough axis combined with intense left exit region of an approaching upper-level jet should support intense lift over extreme SW Norway during the early night hours.
LI's are slightly negative and a few storms could develop due to intense forcing and topographic support, but confidence in more than sporadic thunderstorm development is too low right now and therefore will not highlight any specific area.
Shear would be more than adequate for a severe wind gust threat.