Storm Forecast
Valid: Wed 31 Oct 2007 06:00 to Thu 01 Nov 2007 06:00 UTC
Issued: Tue 30 Oct 2007 21:31
Forecaster: GATZEN

SYNOPSIS

A high is present from west Europe to central Europe. To the south, a trough covers west and central Mediterranean. To the north, quite intense troughs move into Scandinavia, while a high remains over north-western Russia. At lower levels, rather cool air mass affects east Europe, northern Scandinavia, and also a broad region from central Europe to Iberian Peninsula. Warm air mass is present over central and east Mediterranean in the range of the trough center and east of it.

DISCUSSION

Central Mediterranean to southern Adriatic

Latest LIRE Pratica Di Mare sounding indicates that air mass in the range of the Mediterranean trough center is characterized by rich low- and mid-level moisture. Above the 750 hPa level, rather steep lapse rates are present, and deep instability is likely over a broad region. This unstable air mass is forecast to spread eastward on Wednesday, while mid-level lapse rates will slightly weaken. Nevertheless, CAPE up to 1000 J/kg is expected over Tyrrhenian Sea, southern Italy, and southern Adriatic during the period. Thunderstorms will likely develop given weak CIN and some forcing due to low-level convergence. Thunderstorms that form will mostly be non-severe as vertical wind shear will be weak. Given locally steep low-level lapse rates and moderate low-level buoyancy, some waterspouts are not ruled out. Convective activity is forecast to go on during the night and may even intensify as strong upper trough/jet streak moves into southern Adriatic providing strong QG forcing.

Southern Adriatic

In the morning hours, the southern Adriatic is affected by a weak frontal boundary at the eastern edge of the moist air mass situated in the range of the trough. This results in strong vertical wind shear and favorable veering profiles, indicated by 10 m/s LLS and around 140 J/kg 0-1 km SRH. Low-level unstable air mass will be capped near the frontal boundary, and -200 J/kg CIN is forecast by latest GFS model run. Although convective activity is forecast to be rather weak initially, a few isolated storms are not ruled out that will pose a threat of tornadoes, especially where low-level buoyancy is best, i.e. along the frontal boundary/low-level convergence. Threat will gradually weaken during the day as vertical wind shear will weaken while the trough propagates eastward.

Northern Tunisia, Sicily, partly southern Adriatic

Late in the period, strong upper jet streak will move northeastward from northern Africa into central Mediterranean. It will provide strong DCVA, and QG forcing will likely be strong enough for ongoing convective activity spreading from Tunisia to southern Italy during the night. Given strong DLS, thunderstorms may merge into multicells, and even some bowing lines may develop. Strong wind gusts and isolated severe wind gust are forecast, but overall threat seems to be quite weak given rather weak instability.

Greece, Aegean

Ahead of the trough, a tongue of steep lapse rated spreads north-eastward into Aegean. Below a strong capping inversion, moist and unstable boundary-layer is present as indicated by latest sounding over Crete. This air mass is expected to be present over the Aegean Sea during the forecast period.

Persistent WAA and some DCVA in the range of the strong upper WSW flow will likely result in QG forcing, but given strong capping inversion, initiation is questionable. Expect that some convection including thunderstorms will develop, strong vertical wind shear and veering with height will be favorable for supercells. These may be capable of producing large hail, and severe wind gusts locally. Tornadoes are not forecast given rather weak low-level buoyancy.

Northern Baltic Sea

An intense low moves eastward into Scandinavia. The frontal system crosses the Baltic Sea during the night hours, and a well-developed occlusion is expected to move eastward over the northern Baltic Sea and central Finland in the morning hours. A tongue of quite rich low-level moisture will spread into this region, while mid-level cooling is forecast in the range of the propagating trough. This may result in some instability, that will likely be limited to lower levels. However, strong QG forcing may be sufficient for embedded convection in a more stratiform rain band, and even some thunder is not ruled out. Given strong vertical wind shear, isolated severe wind gusts are not ruled out. When low-level buoyancy is also present, strong LLS may also support a tornado. Overall threat is low given weak instability.