Storm Forecast
Valid: Thu 16 Apr 2020 06:00 to Fri 17 Apr 2020 06:00 UTC
Issued: Thu 16 Apr 2020 06:58
Forecaster: GATZEN

A level 1 was issued across Portugal for tornadoes and severe wind gusts.

A level 1 was issued across southern and eastern Spain for hail and severe wind gusts.

A level 1 was issued across southern France for large hail.

A level 1 was issued across north-eastern Algeria and northern Tunisia mainly for large hail and severe wind gusts.

SYNOPSIS

A strong north-westerly mid-level flow is present across northern and eastern Europe, associated with a strongly-forced synoptic situation. The lack of low-level moisture inhibits sufficient CAPE over most places to allow for convective storms. A few weak storms are not ruled out across Finland, Belarus, and parts of western Russia, and are capable of producing severe wind gusts. Potential is too weak for a threat or lightning area.

Most of Europe is still unter the influence of mid-level ridging and stable lapse rates. Two vortices are located across south-western and south-eastern Europe. Especially the south-western one is associated with sufficient CAPE since mid-level lapse rates are steep and low-level moisture is quite high.

DISCUSSION

Portugal

An intense vorticity lobe ejects from the base of the deep trough centered to the south-west of Iberia, providing strong QG forcing spreading from south to north today. Affected air mass is already unstable with thunderstorms going on across southern Portugal and close to the shores. Numerous storms are expected to travel north during the period. Forecast soundings show skinny CAPE profiles combined with strong (10+ m/s) vertical wind shear in the lower levels (0-1 km). Therefore, storms are expected to produce locally severe wind gusts and tornadoes. Tornadoes are most likely over northern Portugal and north-western Spain with highest low-level SRH and curved low-level hodographs. Late in the period, convection will move farther north and gradually becomes elevated over the cool waters associated with a decreasing severe potential.

Southern and eastern Spain, southern France

Some more storms are forecast to form in response to diurnal heating over Spain and France. These can organize due to straight-line and quite strong deep-layer shear. Some large hail and severe wind gusts are forecast, especially if supercells can form.

North-eastern Algeria and northern Tunisia

In a well-mixed, strongly-sheared environment with some onshore moisture advection during the day, CAPE will develop. Over the slopes of the Atlas mountains, some isolated storms are expected. These can organize to multi- and supercells given around 15 m/s deep-layer vertical wind shear. Large hail is forecast with these storms. Additionally, severe wind gusts are expected due to low-level inverted-v profiles.

Northern France to British Isles

Storms that form will not profit from strong vertical wind shear, and severe potential is limited. Main threat will be locally large hail. Storms will become more elevated late in the period due to persistent forcing and steep mid-level lapse rates.

East Mediterranean

Ahead of an intense trough, an elevated mixed layer spreads into the east Mediterranean, with rather weak low-level moisture beneath, so that any CAPE will be strongly capped. Within the base of the trough, some weak CAPE has formed and storms will spread east. Weak vertical wind shear near the trough's base will limit any severe potential.