Storm Forecast
Valid: Wed 06 Nov 2024 06:00 to Thu 07 Nov 2024 06:00 UTC
Issued: Tue 05 Nov 2024 14:08
Forecaster: TUSCHY

A level 1 was issued for parts of the W-Mediterranean mainly for heavy to isolated execssive rain and a few tornadoes.

A level 1 was issued for parts of N Algeria and Tunisia mainly for some hail, heavy rain, gusts and a low-end tornado risk.

SYNOPSIS

A stagnant nordhemispheric 4 wave pattern (well sampled in the latest time-longitude diagram of IFS-ENS) features numerous waves with impressive amplitudes. For us of interest will be a Rossby wave atop the North Atlantic, which dives down into the tropics and another one over Russia which extends down to 40 degree N. In-between those waves, we see a constantly building ridge over Europe with peak H5 anomalies evolving over the North Sea into Scandinavia. At the same time, falling heights to the S (over the W Mediterranean) create a transient high-over low blocking pattern. To summarize all that: the pattern is a rather stagnant one with not much change in the forecast period.

At the surface, a broad high pressure area covers most of Europe. Any synoptic-scale fronts round that high far N and affect N-Scandinavia into Russia.

DISCUSSION

... W Mediterranean ...

As thickness drops atop that area, IFS-ENS indicates a broad member pool of evolving MSLP minima around and SE of the Balearic Islands in response to the approaching upper low.

With 1025 hPa (and more) over NE Spain and lowering pressure to the SE, we see a brisk NE-erly BL flow regime along the E coast of Spain and a more E-erly component over the Balearic Islands, as mass fields respond to the evolving upper low. An area with enhanced 0-2 km convergence signals (with numerous maxima) evolves over and just N and E of the Balearic Islands during the evening and overnight hours (ongoing NWP spread).

We start with isolated thunderstorm activity during the daytime hours over most of the W Mediterranean with a few instances of heavy rain and a low-end tornado (spout) risk.

Thunderstorm coverage and intensity increases during the evening onwards and numerous slow moving thunderstorms bring heavy to excessive rain along structuring convergence zones. Ensemble data places the highest risk S of Barcelona (COSMO) with IFS/ICON shifting the maximum more to the E. Low/mid-layer shear but also DLS all feature weak values with the mean storm motion vector in forecast hodographs residing near the center. Erratic and slow storm motion is forecast.

We added a broad level 1 for the rainfall risk but also for an isolated tornado risk. That level 1 was expanded over NE Algeria and deep into Tunisia, where thunderstorms take profit of MUCAPE in excess of 1 kJ/kg, so some hail/gusts are also forecast next to the mentioned rain/spout risks.
The level 1 was also nudged towards the Spanish coast near Barcelona to account for some coastal convergence with enhanced convection. Further onshore (NE Spain), slow moving convection is also forecast, but weak CAPE and only modest moisture values preclude an upgrade for this area.

Further E into the Tyrrhenian Sea, numerous thunderstorms bring spotty heavy rain and a low-end tornado threat (especially when riding LL convergence zones).