Storm Forecast
Valid: Mon 10 May 2021 06:00 to Tue 11 May 2021 06:00 UTC
Issued: Sun 09 May 2021 22:59
Forecaster: GATZEN

A level 1 was issued across the west Mediterranean mainly for heavy rain and severe wind gusts.

A level 1 was issued across eastern France, central Germany, Denmark, and southern Sweden mainly for severe wind gusts.

SYNOPSIS

A deep trough slowly progresses across western Europe. Its axis with cold and well-mixed maritime air mass will affect the British Isles and the Iberian Peninsula with diurnally driven storms in rather weak vertical wind shear. Ordinary, short-lived thunderstorms are forecast with a weak severe potential. Some non-mesocyclonic tornadoes are not ruled out due to low-level buoyancy and pretty low cloud bases.

Ahead of the trough, a cold front extends from the west Mediterranean to Germany and Denmark. A warm front is located across southern Sweden towards Finland.

DISCUSSION

Germany, eastern France, southern Scandinavia

Along the frontal boundary, rather rich moisture is present that overlaps with modest lapse rates. Weak MUCAPE is forecast over a broad area and elevated storms are forecast along the cool side of the front. In strong deep layer vertical wind shear, these storms will form some organized, rapidely moving clusters with embedded mesocyclones. Main threat will be a local severe wind gust, but also some large hail is not ruled out. On Monday morning, some storms over eastern France and western Germany are also capable of producing brief low-level rotation in a strongly-sheared environment with low cloud bases, posing a weak tornado threat.

Later during the day, strong diabatic heating results in surface-based CAPE on the warm side of the boundary over Germany. Strong shear and rather high LFC with also dry LFC environment make convection initiation unlikely. However, high resolution models suggest one or two splitting storms. 20 m/s deep layer vertical shear supports this storm mode, capbale of producing large hail and severe wind gusts.

West Mediterranean

In the southern parts of the level 1, forecast profiles indicate skinny CAPE, a deep moist and warm cloud layer and low LCLs. Storm motion vectors are mostly parallel to the eastward moving cold front. This poses a threat of heavy rain over southern France spreading eastward during the forecast period. Additionally, a few tornadoes are not ruled out in areas with stronger diurnal heating where strong low-level vertival wind shear can overlap with a low LFC.

Near East

A cut-off trough is located over the eastern Black Sea with a vort-max rotating around its base that affects the Near East. At lower levels, a warm and well-mixed air mass advects northward. During the day, deep mixing will result in inverted-v profiles and models precict weak MLCAPE. Some showers and thunderstorms are forecast to form during the passage of the trough axis. Isolated severe downbursts are forecast with this activity that will rapidly decay in the wake of the trough axis.