Storm Forecast
Valid: Wed 24 Feb 2010 06:00 to Thu 25 Feb 2010 06:00 UTC
Issued: Tue 23 Feb 2010 19:48
Forecaster: PUCIK

A level 1 was issued for Southwest France mainly for severe wind gusts and tornadoes.

SYNOPSIS

An active weather pattern will persist over Southwestern and Western Europe as strong westerly to northwesterly mid and upper tropospheric has overlied the region. Embedded in the flow, two short wave troughs will become a foci for the thunderstorms development over the region. To the east a shallow trough extends over the Eastern Europe with its base over the eastern half of the Mediterranean, where weak upward motion along with warm sea surfaces is expected to contribute to the destabilisation with up to 1000 J/kg of MLCAPE simulated by models. Abundant shower and thunderstorm activity is forecast, especially over the Ionian Sea.

DISCUSSION

... Southwest France ...

In the left exit region of the mid-level jet-streak an upward motion is expected to contribute to the marginal destabilisation over this region. Models agree on the extent of instability, but its degree should stay very limiting, with MLCAPE values probably well below 500 J/kg. On the other hand, forcing from the approaching trough and jet-streak might help in the storm initiation. Wind shear will be mostly confined to the lower levels, with 20-25 m/s flow at 850 and 700 hPa respectively. Degree of deep layer shear will increase to the south, where a strong flow at mid and upper levels will be observed. Nevertheless, with such small degree of instability and wind shear confined to the lower levels, degree of the storm organisation is questionable. With strong flow at lower levels a chance exists that even with weaker and low topped storms, a marginally severe wind gusts might occur or a weak tornado. Low end Level 1 seems to be warranted. The threat should be most prominent between 06-12 UTC on Wednesday.

... Portugal ...

Yet another high wind shear - weak instability situation is expected over this country. After Thursday 00 UTC, with the approach of the surface low from the west, a warm and moist airmass, with enhanced Theta-E values is expected to advect over the region. Marginal CAPE values are simulated along with more or less neutral forcing, so conditions do not seem very favorable for deep moist convection or for its persistence inland. Due to the very strong wind shear, a chance of severe gusts or a tornado would exist, provided some storms manage to thrive inland. For this reason, the question mark remains with this area and at the moment, no Level is introduced. Update, however, might become necessary later on.

... Turkey ...

Locally heavy rainfall event is not ruled out as numerous rounds of showers and thunderstorms are expected to occur, especially close to the coastline. With no organised thunderstorm activity expected, lacking strong synoptic factor and insignificant absolute moisture content in the troposphere, the coverage of severe convective rainfall should stay very localised and does not warrant Level 1 at the moment.