Storm Forecast
Valid: Tue 03 Feb 2015 06:00 to Wed 04 Feb 2015 06:00 UTC
Issued: Mon 02 Feb 2015 23:29
Forecaster: PISTOTNIK

A level 1 and level 2 were issued for parts of the W Mediterranean Sea, the Tyrrhenian Sea, Italy and coastal Algeria mainly for severe convective wind gusts and to a lesser extent for excessive convective precipitation.

A level 1 was issued for the W Balkans for excessive convective precipitation.

A level 1 was issued for NW Spain for severe convective wind gusts and excessive convective precipitation.

SYNOPSIS

Centered around an upper-level low over the southern Baltic Sea, a huge upper-level trough covers almost entire Europe. A series of short-wave troughs pivot around it and spark numerous, mostly small surfaces cyclones.
The bulk of convective activity will be tied to a ribbon of deepening surface lows which extend from the Celtic Sea across the Bay of Biscay and Spain into the western and central Mediterranean region. By the end of the forecast period, the dominant surface cyclone will emerge ocer Corsica and north-central Italy. The minimum pressure forecasts range from 984 to 994 hPa, with the latest Mon 12 UTC runs uniformly showing a more benign scenario.
Warm air advection from the southwest overspreads Italy and the Balkans ahead of this low. Otherwise, polar air has flooded the entire European continent and surrounding sea waters.

DISCUSSION

... W and central Mediterranean, Italy ...

Cold mid-levels on top of the sea water enable some hundred J/kg of CAPE in the range of the ill-defined cold front of the Mediterranean cyclone. In general, weak large-scale lift will be present, but special attention needs to be given to a smaller and more intense vorticity maximum which will probably overspread the cold front in the 12 to 21 UTC time frame. The forecast models agree on robust (convective) precipitation signals over much of the western Mediterranean region.
The wind field strengthens at the southern flank of the deepening low between the Baleares, Sardegna and Algeria, where surface winds are forecast to peak between 20 bis 25 m/s and 850 hPa winds above 30 m/s. A level 2 was issued for a corridor where the strong wind field overlaps with the lift support of the mentioned vorticity maximum, which makes it quite likely that thunderstorms will develop and contribute to the wind risk. Vertical wind shear is very limited, but even disorganized storms may easily produce gusts above 25 m/s in such a kinematic environment. The level 2 is surrounded by a broader level 1, in which severe wind gusts are expected as well but a contribution of deep convection becomes more questionable. In addition, heavy precipitation is possible along windward coasts of Sardegna and south-central Italy. The risks diminish after midnight.

Further north, heavy rainfall and gale- to hurricane-force wind gusts are also expected in vicinity of the low pressure core over the Golfe du Lion, the Ligurian Sea and (later) parts of Corsica, but probably without thunderstorm activity.

... W Balkans ...

Warm air advection ahead of the cyclone enhances 0-3 km wind shear to 10 m/s over the Adriatic Sea and 15 m/s over land, including veering wind profiles. Intensifying orographic and synoptic lift will increase the chances that the precipitation shield will morph into more intense banded structures under the release of limited latent and/or symmetric instability.
By the end of the forecast period, thunderstorms with heavy rain become likely along the western Balkans coasts. Severe wind gusts are not ruled out, either, as the 850 hPa winds come close to 25 m/s.

... Spain ...

In the wake of the Mediterranean cyclone, a band of low surface pressure extends across the Bay of Biscay to the Celtic Sea, and strong Northwesterlies advect maritime polar air with neutral or slightly unstable profiles at its southwestern flank. Showers may become deep enough to produce some lightning strikes.
GFS and ECMWF agree on a secondary low pressure center with a shallow warm core to move onshore near Gijon around 15 UTC. At the southwestern flank of such a feature, severe wind gusts and particularly heavy precipitation with embedded thunderstorms may occur. After a history of heavy snowfalls and with a zero degree level below 1000m, heavy snow and avalanches may block roads and cut off remote villages in the Cantabrian mountains.
Finalizing this round dance of low pressure systems, a sharp trough at all levels will cross Spain from northwest to southeast in the evening and overnight. Synoptic lift ahead of it may maintain weak CAPE well inland, and isolated thunderstorms with a risk of marginally severe wind gusts are possible. The arrival of the trough may also ignite another round of thunderstorms over the far-western Mediterranean Sea towards Wednesday morning.

... Turkey ...

Scattered thunderstorms will go on into the current forecast period in the range of a departing short-wave trough in northwestern Turkey. Activity will diminish or gradually leave our forecast area after 12 UTC. With limited CAPE and weak vertical wind shear, severe weather is unlikely. An isolated waterspout is possible, though.