Storm Forecast
Valid: Mon 31 Oct 2011 06:00 to Tue 01 Nov 2011 06:00 UTC
Issued: Sun 30 Oct 2011 16:25
Forecaster: TUSCHY

A level 1 was issued for the coastal areas of N-Algeria and parts of Tunisia mainly for heavy rainfall.

SYNOPSIS

The weakening trend of the upper low over Tunisia continues but this feature still dictates the weather for that area. Scattered showers and thunderstorms are forecast. An upper trough over the Bay of Biscay assists in some WAA/moisture recovery over the Iberian Peninsula but overall thunderstorm probabilities remain slim. Along this trough, some weak MUCAPE advects all the way to UK/Ireland, but expected coverage of a very isolated thunderstorm does not justify a 15-% lightning area. No organized thunderstorms are forecast for the rest of Europe.

DISCUSSION

... N-Algeria/Tunisia ...

The cyclonic vortex over NE-Algeria/N-Tunisia becomes diffuse and W-E elongated. However, this feature remains in place during the forecast with no real net motion towards the S/E expected. This set-up results in a broad area, supportive for numerous showers/thunderstorms mainly along the coastal areas. No real forcing mechanism can be detected, so the final degree of thunderstorm coverage will probably be dictated on the mesoscale.
Due to the reverse shear flow regime (indicated by forecast soundings of N-Tunisia), any thunderstorm will be a slow mover, which should lead to an augmented heavy rainfall risk with any storm. Quite warm mid-levels/weak lapse rates may also tend to limit the final storm coverage, but confidence is high enough to stick with a 50% lightning area. Thunderstorms keep going all night long.

... Iberian Peninsula ...

A strong trough enters the Bay of Biscay around noon onwards and starts to flatten out while moving to the ENE. Ahead of this trough, some WAA is expected with modest moisture recovery mainly along the S/E-coast of Spain. A strong front enters NW-Spain/Portugal during the late morning hours onwards but it starts a rapid weakening trend during the following hours, while moving further onshore. So overall conditions for isolated thunderstorm development are marginal at best. No severe risk is expected with that convection and a 15% lightning area seems to cover that activity.