Storm Forecast
Valid: Tue 27 Jun 2023 06:00 to Wed 28 Jun 2023 06:00 UTC
Issued: Mon 26 Jun 2023 22:06
Forecaster: GATZEN

A level 1 was issued across northern Italy for large or very large hail and severe wind gusts.

A level 1 was issued across the northern Balkans maonly for large hail and severe wind gusts and locally heavy rain.

A level 1 was issued across the Caucasus region for large or very large hail and severe wind gusts.

A level 1 was issued across north-eastern Spain for severe wind gusts.

DISCUSSION

Northern Italy

At the southern edge of the forming cut-off trough, the anticyclonically sheared flank of the jet streak spreads across the eastern Alps. The approaching cold front will cause some lift before cold air advection sets in from the north and east. The affected air mass is unstable due to rich low-level moisture and steep low- to mid-level lapse rates. CAPE will be highest in the north-west, whereas deep-layer shear increases to 20 m/s in the east.

Initiation is expected in the afternoon along the slopes of the Alps, with some supercells possible due to locally enhanced deep-layer shear. These can move south-east what would result in high-based storms capable of large or very large hail and severe wind gusts. However, most of the storms may be less organized due to limited vertical wind shear and may cluster ahead of the approaching cold front. Some large hail and severe wind gusts are forecast before storms decay overnight.

Northern Balkans

Cold air advection spreads south-east rather quickly, affecting a cold front in the morning that will likely loose some of its convergence field. Diurnal heating will support some frontogensis during the day, and new thunderstorms are expected to develop. Storm motion vectors are perpendicular to the front so that these can cluster. 0-3 km shear supports some bowing segments especially in the northern part of the level 1, where severe wind gusts and heavy rain are forecast. From Slovakia to Romania and north-eastern Hungary, CAPE-shear overlap is favorable for some multicells and also brief supercells. Locally, large hail is forecast, and severe wind gusts and heavy rain are additional threats due to inverted-v-profiles and high cloud bases associated with wide updrafts. Later in the day, cold air advection will likely cause a weakening of the convective activity.

Caucasus area

Ahead of the south-east-European cut-off, a strong mid-level flow is located over the Caucasus region. At lower levels, a cold front spreads south with a band of frontal lift affecting a rather moist and unstable air mass. Convection initiation is forecast due to a rather moist LFC, and long, straight hodographs support some spitting storms, with right movers staying ahead of the cold front and moving upslope towards the Caucasus. These storms can produce large or very large hail and severe wind gusts, although CAPe is limited to below 1000 J/kg.

North-eastern Spain

In a well-mixed air mass, the diurnal mountain-valley circulations can become more effective in initiation due to a short-wave trough that promotes some QG lift together with a cold front moving south across France. Vertical wind shear is weak, and storms are not expected to organice. Severe wind gusts are still forecast locally due to deep inverted-v profiles. With less probability, the same potential exists across parts of the Atlas mountains.

Northern Sweden

In a weakly-sheared environment with weak CIN, non-mesocyclonic tornadoes are forecast. Additionally, local downbursts can result in some marginally severe wind gusts.