Storm Forecast
Valid: Fri 08 Nov 2024 06:00 to Sat 09 Nov 2024 06:00 UTC
Issued: Thu 07 Nov 2024 19:52
Forecaster: TUSCHY

Numerous level 1 areas were issued for parts of the W/CNTRL Mediterranean mainly for heavy rain and a low-end tornado risk.

SYNOPSIS

An impressive anticyclone over Scandinavia dominates the forecast period with peak anomalies in the 500 hPa height field centered over CNTRL Norway/Sweden.

A weak upper trough over W Europe/the W-Mediterranean Sea splits into a SE ward shifting wave, which crosses Tunisia and the Gulf of Gabes SE into Libya and into a leftover over France. In addition, a compact cold-core low rounds the base of the antiyclone and crosses CNTRL Europe from E to W/NW.

Although only weak/transient, some models insist on a broad LL vortex atop the northern Western Basin, which is also seen in a few IFS-ENS members.

The main synoptic front, which is accompanied by at least some thunderstorm activity is a weakening cold front, which crosses the Bay of Biscay E.

DISCUSSION

... W/CNTRL Mediterranean ...

An already worked-over marine air mass beneath weak mid-level lapse rates create some MUCAPE on the order of 200-600 J/kg. Lapse rates increase a bit towards NE Algeria/Tunisia with up to 1000 J/kg.

The main driver for numerous thunderstorms will be the weak gyre S of France and mesoscale convergence zones S of the Ligurian Sea into the Tyrrhenian Sea.

Slow/erratic storm motion is forecast and heavy rain on a local scale is the main hazard. Neither the geometry of the vortex nor the convergence zones are well handeled in NWP data. We expect the highest thunderstorm and rain threat from the Golf de Lion E into the Corso-Ligurian Basin, which is also in line with the latest ensemble/deterministic runs. The same for the E coast of Corsica and E/SE.

In case we see an onshore pointing convergence zone towards E Corsica and far S France, we could see a few excessive rain events in excess of 100 l/qm/24h on a local scale. This is also valid for S/SE Sicily.

An isolated tornado (spout) event is possible.

... S Bay of Biscay ...

A few slow moving and clustering thunderstorms bring heavy rain on a local scale, which is not enough for an upgrade for now. Peak amounts occur probably around and E of Bilbao, where strongest coastal convergence signals exist.