Storm Forecast
Valid: Sat 03 Nov 2012 06:00 to Sun 04 Nov 2012 06:00 UTC
Issued: Fri 02 Nov 2012 18:17
Forecaster: TUSCHY

A level 1 was issued for parts of Portugal and Spain mainly for heavy to locally excessive rainfall amounts.

A level 1 was issued for the coastal areas and far SW-Spain mainly for an isolated large hail, strong wind gust and isolated tornado risk.

SYNOPSIS

An extensive cyclonic vortex over N-Europe steers numerous disturbances over most of Europe, which are embedded in a brisk W/SW-erly flow. Weak ridging continues over SE Europe with less shower activity affecting those regions. With a significant negative anomaly of the blocking index present throughout the forecast period, no major pattern change is expected for the time-frame of interest.

Again, isolated to scattered thunderstorms are forecast beneath the cold core vortex, where either forcing, mid-level temperatures or regionally enhanced SSTs favor deep and electrified convection over offshore areas of NW Europe. Beside a few strong wind gust events with that convection, the overall activity remains sub-severe.

The only area of interest in respect of organized convection arises in the entrance region of a phased jet just west of Portugal. The advected air mass reveals true tropical characteristics with TPWs in excess of 50 mm and weak mid-level lapse rates. However, impressive moisture even offsets weak lapse rates and therefore a tongue of 800 J/kg MLCAPE may approach SW Portugal during the day. Showers and thunderstorms repeatedly move ashore and obviously carry a heavy to excessive rainfall risk far inland. We would not be surprised to receive a swath of 50-100 mm/24h reports far inland and hence a rainfall-level 1 was expanded far east.
Beside the rainfall risk, DLS of 20 m/s is adequate for a few organized thunderstorms with isolated large hail (despite the tropical nature of the air mass, but with ongoing influx of cooler and drier extratropical air from the north at mid-levels) and strong wind gusts (weak lapse rates at all levels may lower downward impuls and therefore also the severe wind gust risk). An isolated tornado is possible along the coastal areas within the level 1. The thunderstorm risk continues all day long.

Further east, over the W-Mediterranean, conditions for DMC improve after 00Z and despite reluctant model QPFs, a broad lightning area was added, mainly due to roughly 500 J/kg MLCAPE and diffluent upper flow. DLS of 20 m/s would support an isolated better organized thunderstorm event, but expected coverage and still limited confidence in CI preclude any level area for now.