Storm Forecast
Valid: Mon 07 Nov 2011 06:00 to Tue 08 Nov 2011 06:00 UTC
Issued: Sun 06 Nov 2011 16:53
Forecaster: TUSCHY

A level 1 was issued for the W-Mediterranean mainly for heavy rainfall. Isolated excessive rainfall is possible.

A level 1 was issued along the E-coast of the Adriatic Sea mainly for heavy rainfall and waterspouts.

SYNOPSIS

The extensive upper low over the Mediterranean remains in place during the forecast. High over low blocking pattern persists and precludes any thunderstorm probabilities outside the Mediterranean area.

A side note:
The past model runs converged with their handling on the low pressure area over the W-Mediterranean. Phase diagrams indicate that a shallow warm core structure may have formed in the past 12 h and some further organization is possible. However, no model now indicates reliable probabilities for an enhanced chance of a deep warm core structure. Nevertheless this system already revealed some banding structure with active convection along those bands (especially along the southern/eastern part). There is plenty of time left that this system could still acquire some better organization/structure. In case those convective bands starts to wrap around the center and become better organized, some kind of classification can be carried out. Most models loop this depression first to the east and later in the period northwards to the coast of S-France (remaining still offshore until 06Z).
An update may be issued, if further organization unfolds.

DISCUSSION

... W-Mediterranean ...

The aforementioned depression over the W-Mediterranean will be the main focus for severe convection. DLS atop that cyclone decreases to less than 10 m/s, whereas areas like S-France, Corsica and Sardinia may see DLS up to 15 m/s. A lot depends on how structured that cyclone gets to define any heavy rainfall probabilities. Right now the highest risk for excessive rainfall exists over the Balearic Islands as the center of the depression moves off to the east quite slowly. Any thunderstorm, which develops atop those islands experiences a very weak steering flow with 15m/s 850 hPa winds, so slow moving/training storms are possible. Similar conditions are expected over Corsica and Sardinia despite somewhat stronger shear. Numerous slow moving showers/thunderstorms are forecast to affect the area and excessive rainfall is well possible.
No level 2 was added due to uncertainties in the mesoscale and still ongoing questions how far the depression organizes, however coastal areas of S-France may need an upgrade later on.

During the night, the heavy rainfall risk may als increase along the coastal areas of S-France and onshore, as the depression approaches from the south. Right now we think that the flow remains more parallel to the coast, which may limit the risk for repeatedly onshore moving storms. However we can't exclude some slow moving or even training activity over S-France with 15-20 m/s 850 hPa winds and adequate moisture advection and hence the level 1 was expanded onshore. Also far NW-Italy was included with showers/thunderstorms spreading onshore, producing convectively enhanced rainfall.

... Adriatic Sea ...

Yesterday's front gradually decays with ongoing S-erly winds. Some moisture convergence along the coast of the E-Adriatic Sea is forecast with isolated to scattered thunderstorms possible. Heavy rainfall may accompany stronger storms, but a decrease in thunderstorm activity is expected as the coldest air mass at mid-levels departs to the north. Waterspouts are a possibility along the coast with enhanced LL CAPE and expected coastal wind convergence zones. Hence a level 1 was issued to cover the heavy rainfall and waterspout risk.