Storm Forecast
Valid: Thu 03 Oct 2019 06:00 to Fri 04 Oct 2019 06:00 UTC
Issued: Wed 02 Oct 2019 23:40
Forecaster: GATZEN

A level 2 was issued for Greece and surroundings mainly for excessive precipitation, large hail, and severe wind gusts.

A level 1 was issued for the Aegean and Ionian Sea region mainly for large hail, severe wind gusts, and excessive precipitation.

A level 1 was issued for southern Italy, Albania, and the southern Adriatic mainly for waterspouts and excessive precipitation.

SYNOPSIS

An amplified trough migrates across Europe, and its southern edge will affect the Mediterranean. Ahead of the trough axis, a strong southerly low-level jet transports warm and moist air masses towards Greece and the Aegean. While a capping inversion will suppress convection initiation initially, strong QG forcing reduces CIN from the west during the period, and thunderstorms are expected along and ahead of an approaching cold front.

Quiescent conditions are forecast for most of Europe, except for some cold sector thunderstorms in the wake of the North and Baltic Seas. Late in the period, the remnants of Hurricane Lorenzo will affect Ireland.

DISCUSSION

Greece and Aegean Sea area

Widespread thunderstorms are forecast to spread eastward during the period. Latest models indicate large CAPE in the hail growth zone and also 20 m/s deep-layer vertical wind shear, supportive for large or very large hail with any supercell that forms. Main storm mode will be mesoscale convective systems that propagate eastwards. Next to large hail, severe wind gusts are forecast given strong 0-3 km vertical wind shear. Additionally, flash floods become increasingly a threat during the period, especially where upslope flow is present.

The northern Aegean Sea is also affected by excessive convective precipitation. Here, skinny CAPE profiles, high precipitable water, and storms moving along the same convergence zone for some time are forecast.

Southern Adriatic and Albania, Ionian Sea, southern Italy

Close to the trough axis, thunderstorms are forecast due to rich low-level moisture and steep lapse rates in relatively cold air over warm waters. Vertical wind shear is mostly weak. Locally, excessive rain is possible. Waterspouts are forecast in particular in the morning when land-breeze convergence lines are foci of convection.

Bulgaria, Romania

Some thunderstorms are forecast in a southerly flow that advects rich low-level moisture northwards. Additionally, steep lapse rates are shown by latest models. Vertical wind shear is mostly below 10 m/s and storms will be only weakly organized. Locally, excessive rain and some large hail are forecast.

Benelux and north-west Germany

Diurnally driven showers and thunderstorms are forecast on Thursday close to the western edge of the European trough, possibly due to low-level stretching below an upper-level front. Low-topped convection is expected. Effective shear is weak despite strong 0-6 km deep-layer shear. Weakly organized storms are forecast. Main threat are some non-supercell tornadoes or waterspouts given weak low-level shear and rather strong low-level buoyancy.

Ireland

Ex-hurricane Lorenzo moves on-shore late in the evening. Ahead of its center, a moist and unstable air mass is advected towards Ireland. Some 10s J/kg MLCAPE can develop, but instability is rather shallow and convective storms are not forecast. However, potential for some tornadoes is expected given strong low-level vertical wind shear.