Storm Forecast
Valid: Thu 11 Dec 2014 06:00 to Fri 12 Dec 2014 06:00 UTC
Issued: Wed 10 Dec 2014 23:22
Forecaster: GATZEN
A level 2 was issued for southern Turkey mainly for excessive precipitation
A level 1 was issued for the southern Aegean Sea and the east Mediterranean, mainly for excessive precipitation. Furthermore, tornadoes, severe wind gusts, and large hail can occur.
SYNOPSIS
A south-Mediterranean trough moves north-east and will affect Turkey and the Aegean Sea. Central Europe is crossed by a short-wave trough that is pushed east ahead of a strong Atlantic jet streak approaching over western Europe.
DISCUSSION
Southern Aegean, southern Turkey and east Mediterranean Sea
A closed low moves from the south Mediterranean Sea towards Greece. A strong mid-level jet streak curves around its periphery and extends into the east Mediterranean and Turkey at Thursday evening. The associated surface low pressure system will also move north-eastward, yielding warm air advection from Turkey into the Aegean Sea. An elevated mixed layer is expected to spread northward and will partly overlap with a moist easterly low-level flow. CAPE in the order of 500 to 1000 J/kg may realize to the south of Turkey in the evening hours. Placed below the anticyclonically sheared flank of the mid-level jet, subsidence limits the chance of initiation, but every storm that forms will rapidly organize given 25 m/s deep layer vertical wind shear. Large hail and severe wind gusts are the main threat if well-developed multicells and supercells form. Late in the period, the increasing low-level jet may feed training cells capable of producing excessive rain. Together with upslope flow over southern Turkey, severe flash floods may result. Due to the strong low-level vertical wind shear, severe wind gusts and tornadoes are not ruled out.
To the west of the elevated mixed layer, instability is also possible in the moist warm advection regime. Strong DCVA will support lift and steepening lapse rates across the southern Aegean Sea. Storms that form will likely organize given rather strong vertical wind shear, and a few hail and wind events are expected. Additionally, tornadoes are forecast given the strong low-level vertical wind shear. The threat spreads east during the period.
Thunderstorms are also forecast near the centre of the Mediterranean trough. Cold mid-level air is associated with steep lapse rates over the warm sea surface, and low-level moisture is expected to be high enough to enable thunderstorm development. Vertical wind shear is limited, but storms may produce excessive rain locally. Additionally, waterspouts are possible.
North-western Europe
An intense polar trough is located across north-western Europe. A very strong mid-level jet extends from the Northern Atlantic to the British Isles and into central Germany on Thursday evening. Downstream, a short-wave trough moves eastward across central Europe in the evening hours.
Main convective activity will go on across the North Sea region due to the warm sea surface and cold mid levels, leading to steep lapse rates. The strong low-level vertical wind shear due to the large pressure gradient may support low-topped mesocyclones capable of producing tornadoes near the coasts. Additionally, severe wind gusts are likely. However, the contribution of deep moist convection will be weak. A level 1 is therefore not introduced.
At the southern edge of the mid-level cold air, some marginal instability is expected to develop across northern Germany in the afternoon and evening hours, where a few showers or thunderstorms are forecast. The weak low-level moisture is expected to limit the potential, and severe storms are not expected. As the trough moves east, some storms are not ruled out across the Baltic Sea where lapse rates increase again over the warm sea surface.
