Storm Forecast
Valid: Thu 15 Aug 2013 06:00 to Fri 16 Aug 2013 06:00 UTC
Issued: Wed 14 Aug 2013 22:13
Forecaster: GATZEN

A level 1 was issued for parts of the central Mediterranean mainly for large hail and excessive precipitation.

A level 1 was issue for north-eastern Spain mainly for large hail.

SYNOPSIS

The flow across Europe forms a lifting trough centred across Finland that extends into the central Mediterranean. A cut-off low moves eastward along the southern part of the long-wave trough. A new Atlantic trough will enter the British Isles late in the period. At lower levels, northerly winds have advected cold air into most of Europe except for the Black Sea region and Iberia. Rich low-level moisture is only present across the Mediterranean Sea.

DISCUSSION

Tyrrhenian Sea, Ionian Sea, and surroundings

The cut-off low moves across the central Mediterranean. Cold mid-level air and the warm sea surface lead to steep lapse rates as indicated by latest soundings. Although northerly low-level winds lead to the advection of dry air, rich boundary-layer moisture can build over the warm sea, and CAPE up to more than 2000 J/kg is likely.

Along land/sea breeze convergences, convective initiation is likely given the weak capping inversion. Vertical wind shear will be weak with 10 m/s in the lowest 6 km. However, large CAPE and at least some veering will allow for quite intense storms. Large hail and excessive precipitation seem to be the main threat. However, storm clustering may result in a severe wind threat as well. Additionally, storms that can interact with sea-breeze convergences may be capable o producing tornadoes. Storm activity will likely spread eastward with the mid-level trough and will go on across the sea until the morning hours.

Romania to southern Balkans

The cold front of the European trough will slowly move south-eastward into Romania and the southern Balkans. Together with the cooler air, some moisture will spread into the area from the north-west, allowing for diurnally driven thunderstorms over the mountains. Decreasing lapse rates behind the cold front and weak vertical wind shear will limit the severe potential of these storms. Along the cold front, storms are quite unlikely due to the weak moisture. However, every storm that forms in the prefrontal air mass will have a potential of producing dry microbursts due to the deep boundarylyer.

North-western Spain

Upslope advection of Mediterranean moisture and steep mid-level lapse rates will lead to CAPE in excess of 500 J/kg across north-eastern Spain. The cap may break across the mountains over north-eastern Spain during the afternoon hours, and some storms are not ruled out. These storms may produce locally large hail given 10 m/s vertical wind shear in the lowest 3 km. Storms will decease after sunset due to only weak large-scale support.