Storm Forecast
Valid: Fri 09 Jan 2009 06:00 to Sat 10 Jan 2009 06:00 UTC
Issued: Thu 08 Jan 2009 18:43
Forecaster: TUSCHY

SYNOPSIS and DISCUSSION

Stable pressure configuration over Europe persists with an expansive surface high pressure over central Europe, a frigid but dry and stable airmass over NE Europe and a southward digging upper low over Spain and Portugal. This constellation limits thunderstorm probabilities to the central and southern Mediterranean. As a flat and gradually filling upper trough over N-Algeria moves off the coast, the atmosphere becomes unstable with some low-end instability release. The strongest low-level convergent signals are present over the Balearic Islands and next to SW/S-Sardinia with a lull in between. However, a near uncapped airmass and weak forcing from the south mark the environment, so we went with a broad highlighted area. The shear remains weak and the main concern is the gradual build-up of LL instability and weak background flow, so waterspouts are possible. If morning soundings (e.g.Palma de Mallorca or Cagliari) confirm this risk, we have to consider an upgrade.

A surge of moist air to the north just south of Sicily due to a weak depression SE of Tunisia bears another focus for enhanced thunderstorm chances during the late afternoon hours onwards. Higher surface dewpoints work against warmer mid-levels/stronger capping but models like GFS seem to have a good handling regarding expected surface moisture (SST still around 18°C). Deep shear around 20-25m/s would require higher probabilities due to an isolated severe thunderstorm risk, but the best environment for organized storm looks like to be just out of our forecast area. A level area may be included later on.