Storm Forecast
Valid: Thu 22 Jan 2015 06:00 to Fri 23 Jan 2015 06:00 UTC
Issued: Wed 21 Jan 2015 23:15
Forecaster: GATZEN

A level 2 was issued for the Ionian Sea, western Albania, western Greece, and parts of southern Italy mainly for severe wind gusts.

A level 1 was issued for the southern Adriatic Sea region mainly for severe wind gusts.

A level 1 was issued for eastern Tunisia, Sicily, and the Ionian Sea and surroundings mainly for severe wind gusts, large hail, and tornadoes.

A level 1 was issued for Sicily, northern Tunisia, and northern Algeria mainly for excessive convective precipitation.

SYNOPSIS

A sharp long-wave trough is placed across western and central Europe. It yields a southerly to south-westerly flow across eastern Europe. Rather cold air masses spread into western Europe, whereas mild air affects eastern Europe. Limited moisture is expected across western Europe, where isolated storms may develop across the Bay of Biscay on Thursday morning. Across eastern Europe, cold low-level air limits potential of thunderstorms.

DISCUSSION

Tunisia to southern Italy, Ionian Sea, Greece, Albania

A deep trough has formed across Europe, with an axis from Norway to eastern Iberia into Algeria. A strong northerly jet streak feeds the trough on Thursday morning and it amplifies even further into northern Africa. The strong jet streak curves around the base of the trough, pushing a negatively tilted short-wave trough across the central Mediterranean. It will cross the Aegean until Friday morning. Except for a tongue of 8 g/kg mixing ratio ahead of the short-wave trough, low-level moisture is limited, but will partly overlap with steeper lapse rates advected from northern Africa, and CAPE of 500 J/kg is expected.

First storms may develop near centre of the surface low between Tunisia and Sicily, and this activity can spread north-eastwards along the warm air advection regime. But main activity is forecast to be associated with the cold front that quickly moves north-east in the afternoon. A MCS is forecast that builds south-east along the cold front. It is expected across Greece and the southern Adriatic in the evening hours.

25 m/s deep layer vertical wind shear and near 10 m/s low-level shear are forecast by latest GFS and storms can become well-organized along the cold front. The leading gust front can become severe with wind gusts in excess of 25 m/s over a broad area, with peak gusts exceeding 33 m/s. The highest potential is expected along the western coasts of Greece and Albania, but also southern Italy can be affected. Tornadoes and large hail are not ruled out, especially in during the initiation stage of the MCS. Excessive precipitation across southern Italy may be another threat, but mostly associated with stratiform precipitation.

The severe weather threat is expected to weaken during the night hours when the cold front moves into more stable air masses further north-east. Severe wind gusts are possible across the southern Adriatic Sea region, though.

Northern coasts of Algeria and Tunisia

In the wake of the string Mediterranean low, thunderstorms will affect northern Africa due to cold mid-level air masses and rather moist maritime air masses at low levels. Limited vertical wind shear is not expected to assist storm organization, but numerous rounds of storms are expected to increase the potential of excessive convective precipitation. Flash floods are possible especially late in the forecast period.