Storm Forecast
Valid: Sun 18 Nov 2007 06:00 to Mon 19 Nov 2007 06:00 UTC
Issued: Sat 17 Nov 2007 22:59
Forecaster: DAHL

SYNOPSIS

The intense large-scale upper low over the central Mediterranean will slowly progress eastwards while an Atlantic upper trough will evolve into an equally large/intense upper cut-off cyclone, centered over the Channel region by early Monday morning. SFC maps on Sunday are forecasted to feature a weakening low pressure system associated with the Mediterranean upper low, and an eastward-moving, fairly intense system associated with the Atlantic upper feature. High pressure persists over NE Europe.

DISCUSSION

... Ionian Sea ... Aegean Region ...

It seems that the cold front trailing from the SFC low over the S Balkans will become increasingly ill-defined, and convective activity will become increasingly detached from the frontal system. Decaying, partly still severe, MCSs should linger over the E Aegean and W Turkey at the beginning of the period. As the air mass will remain at least weakly unstable over the Aegean region as well as over the Ionian Sea, thunderstorms should persist during the period. It seems that weaker instability/shear and less focused low-level mesoscale forcing for ascent than on Saturday will limit the degree of organization of the convection. However, steep low-level lapse rates will remain in place, so that a couple of waterspouts are likely in the coastal regions of S Italy and Greece. Over the E Aegean/extreme W Turkey, LLS/DLS should at least initially remain fairly strong, so that a few severe, and possibly tornadic, mesocyclonic storms may occur there.

... N Gulf of Biscay ... W Channel ...

A couple of lightning strikes could accompany the cellular polar-air convection which moves towards the N Biscay. Given shallow nature of the storms, lightning frequency may be quite low, but a thunderstorm area appears to be marginally warranted. There is some threat for a brief tornado or two over the French NW coast late in the period as strong LLS will be in place. However, threat should be too low for a categorical risk.