Storm Forecast
Valid: Thu 17 Jul 2008 06:00 to Fri 18 Jul 2008 06:00 UTC
Issued: Wed 16 Jul 2008 21:44
Forecaster: GATZEN

SYNOPSIS

Large trough extends into Europe east of a strong ridge over the northern Atlantic Ocean. As a consequence, cool maritime air mass has spread into most parts of northern and western Europe. A frontal boundary extends from Bay of Biscay to the Alps, Belarus and western Russia. South of the main frontal boundary and associated mid-level jet stream, upper troughs are present over west Mediterranean and northern Black Sea.

DISCUSSION

... South-west Mediterranean ...

Again, severe convection is forecast across south-west Mediterranean. Another strong mid level jet streak is expected to curve around the upper trough that starts to accelerate eastwards. Strong DLS is forecast especially along the African coast, where 0-6 km vertical wind shear is forecast to reach 40 m/s. But strong DLS is also forecast over south-west Mediterranean Sea as well as over the Atlas mountains. Affected air mass is characterized by steep mid-level lapse rates, while boundary-layer moisture is maximized over the sea. Moisture advection is forecast over northern Africa during the period, as north-easterly winds will evolve north of the low surface pressure. Upslope flow and convergence along the central Atlas will likely assist for initiation again, and given strong DLS, supercells are forecast, capable of producing large hail and severe wind gusts. Best chances for tornadoes are expected over the warm sea surface. Convection will likely spread eastward ahead of the approaching trough axis, while severe threat is forecast to decrease gradually as storms will become more elevated.

... Northern Italy ...

South of the Alps, warm air mass is characterized by relatively rich low-level moisture. During the period, upper trough axis will cross the region, and upper height falls and diurnal heating will likely result in some CAPE of several 100s J/kg in the afternoon hours. Forcing is likely underneath an upper westerly jet streak and propagating cold front. Thunderstorms that form may evolve into supercells given strong DLS. Isolated severe hail and wind gusts are not ruled out with the stronger storms. Limiting factor will be rather weak veering profiles, limited instability and cold air advection late in the period, when storms are forecast to move into northern Balkans, where convection may merge into an MCS.

... Western Russia to northern Black Sea region ...

Along the eastern frontal boundary, unstable air mass is present as indicated by latest ascends. Steep low-level lapse rates and rich boundary-layer moisture are present just east of the frontal boundary. In contrast to yesterday, DLS is forecast to be rather strong as upper southerly jet streaks will eject from south-east European cut-off low. Rather strong LLS is also expected from north-eastern Ukraine to western Russia. Convection will likely develop during the day, and supercells are expected to be capable of producing large or very large hail given high CAPE during the day. Additionally, severe wind gusts may occur. Near the frontal boundary, a few tornadoes are not ruled out given stronger LLS, especially near the warm front over north-western Russia, where even strong tornadoes are not ruled out.
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