Storm Forecast
Valid: Thu 27 Jun 2024 06:00 to Fri 28 Jun 2024 06:00 UTC
Issued: Wed 26 Jun 2024 21:42
Forecaster: TUSCHY

A level 2 was issued across CNTRL Germany into Denmark for numerous excessive rainfall reports.

A level 1 surrounds the level 2 for similar hazards but with lower probabilities. A few hail and strong to severe downburst events are forecast next to a low-end tornado risk.

A level 1 was issued for parts of SW France mainly for a few large hail and heavy rain reports.

SYNOPSIS

A blocking anticyclone over Scandinavia steers a cut-off from the Alps to the SE. In the meantime, an unseasonably strong cut-off over Portugal reaches its lowest latitude before it starts to lift NE during the end of the forecast.
The Mediterranean will see capped conditions beneath a strong subtropical ridge.

At lower levels, a pronounced LL convergence zone over parts of CNTRL Europe becomes the focus for most active thunderstorm initiation. A slow moving cold front crosses Benelux during the day eastwards and approaches NW Germany during the end of the forecast.

DISCUSSION

... Germany and Denmark...

A filling upper trough atop a broad low pressure channel (tilted from Benelux to the SE) with BL mixing ratios in excess of 12 g/kg create a favorable setup for slow moving convection. Some CAMs show a broad /diffuse LL depression over CNTRL Germany, which dissolves during the day and becomes the focus or virtually no storm motion for initiating storms.

Abundant deep moist profiles with PWs in excess of 30-35 mm beneath neutral mid-level lapse rates create MUCAPE values in the 1-2 kJ/kg range.
As the upper trough lifts N/NE during the day, a drier airmass from France sneaks into W-Germany. Good diurnal heating/mixing results in lowering moisture content throughout most of the troposphere with LL winds turning straight W. This places the deepest moisture plume from E-CNTRL into N Germany.

CI occurs already early in the day with near uncapped conditions (e.g. along the orogrpahy) but becomes most focused along the low pressure channel, especially as LL winds turn W along its western fringe.

Scattered to widespread slow moving thunderstorms occur with heavy to excessive precipitation and local flash flood issues. In addition, initiating cells can temporarily produce some hail and a strong (wet) downburst or two. Somewhat enhanced LLCAPE indicates an isolated short-lived tornado event over CNTRL Germany but also along the convergence zone up to Denmark.

The highest (but still localized) flash flood risk evolves within the level 2 area, which runs along the LL convergence zone and offers deep/strong convergence.

... SW-France ...

A building ridge atop a very moist BL air mass features capped 1-2 kJ/kg MUCAPE. A short-wave rides E along the crest of the ridge and could spark a few thunderstorms, which would bring large hail and heavy rain to the highlighted area. However, a substantial model spread persists with QPF of various NWPs, as EZ driven models even show an eastward moving MCS event, driven by nocturnal convection over the S-Bay of Biscay.

... Balkan to Poland ...

Similar to Germany/Denmark, widespread MUCAPE in the 1-2 kJ/kg range with weak shear support slow moving storms with heavy to excessive rain and hail. A few strong to severe downburst events area possible as well as a low-end tornado risk especially towards the Balkans. There is no clear focus in model guidance for a concentrated area with level 2 conditions (e.g. for flash flooding), but local/temporal level 2 conditions can exist within this broad level 1 area.

... Portugal ...

During the overnight hours, some banded convection along the periphery of the cut-off could bring a few heavy rain and hail issues with modest MUCAPE/shear, but expected coverage does not yet justify an upgrade.