Storm Forecast
Valid: Tue 06 Oct 2026 06:00 to Wed 07 Oct 2026 06:00 UTC
Issued: Mon 05 Oct 2026 16:50
Forecaster: TUSCHY

Two level 1 areas were issued across most of the W/CNTRL Mediterranean to SW Spain/SE Portugal for heavy to locally excessive rain with an isolated tornado risk. The tornado and gust risk is maximized over far S-Spain and next to the Balearic Islands during the night.

SYNOPSIS

A mobile anticyclone crosses CNTRL Europe E and is followed by a longwave trough, which emerges from the NE Atlantic.

A complex dynamic pattern frames this basic large-scale wave pattern with a strong upper-level positive PV anomaly (cold-core vortex) over the Alps steered N into SE Germany. This vortex in turn steers a weak but deep W-erly flow regime over the W Mediterranean during the initial phase of this forecast. An embedded shallow positive PV anomaly enters the Tyrrhenian Sea and serves as focus for organized DMC activity.

Betimes, a broad positive PV anomaly over SW Europe gets caught by the mentioned IPV lobe/upper trough from the W, resulting in a broad cyclonic gyre over W Europe, which gradually takes over the steering flow regime over the far W Mediterranean (brisk SW-erly flow regime). This evolution steers a plume of rich/deep tropospheric moisture from the SW Mediterranean towards W France betimes.

DISCUSSION

... W Mediterranean ...

A multifacet severe risk evolves over different parts of the area of interest.

NE Spain (including the recently hard hit areas surrounding Barcelona) see temporarily improving conditions for training near coastal convection, which also achieves some better probabilities for storm organization. This risk depends however on how well structured a passing short wave will be. The temporal backed/southerly flow advects the moist/unstable marine layer ashore and also increases LL SRH, so expect a mix of slow moving/partially training coastal cells with heavy to locally excessive rain. A few rotating cells are als possible along the coast/offshore with a severe gust/tornado and local hail risk. The risk subsides from W to E during the night.

This event is a borderline level 2 one mainly due to the lingering impacts from the past rain event (ref. to EFAS), however the short time slot for persistent/modest onshore flow kept this in a level 1 for now. An isolated signifcant flash flood event is possibe if a stalling storm meets an urban area during the daytime hours.

Further N towards the Gulf of Leon towards the Cevennes, lowering MSLP over the Bay of Biscay results in another onshore flow event. Stalling thunderstorms along the orography (like te Cevennes) produce another nocturnal heavy rain event. 50-150 mm will be common in 12h with local peaks hovering around 250 mm, so flash flooding is possible. This area is used to such rainfall amounts and relaxed hydro conditions are noted. In addition, this event ends during the end of this forecast, so we kept this in a level 1 for now. Still, a significant flash flood event is possible.

Towards the Tyrrhenian Sea, a sprawling/slowly eastbound moving LL positive PV anomaly sparks persistent/long-lived thunderstorms with excessive rain mainly confined to the offshore areas. We expanded the level 1 towards the coast as we cannot exclude more aggressive storm motions on the local scale with MCV/cold pool development, which would expand the training risk also near the coasts.

We added a separate level 1 for parts of SE Portugal to S Spain mainly for a tornado and heavy rain risk. During the daytime hours, gradually relaxing LL SRH works against diabatic heating with lowering inflow layers and an isolated tornado is possible.

The tornado risk increases during the overnight hours over far S Spain, as backed BL flow advects a very moist airmass ashore (offshore areas with +3C SST anomalies) and hampers BL stabilization. Strong WAA regime results in curved hodographs and any more discrete cell has the chance to become supercellular with a severe gust/tornado and heavy rain risk. This activity spreads towards the Baltic States during the end of the forecast and upscale growing clusters could produce swaths of severe gusts. This could indeed become a level 2 candidate, but there remain uncertainties if this clustering takes place before or after 06Z. Anyhow, beyond 06Z there will be a growing severe guts threat over and N of the Balearic Islands (beyond SWODY1).

... W France ...

A plume of subtropical air resides and also gets advected towards W France as increasingly divergent upper levels overspread that area in respone to the structuring/lifting upper trough. Forecast soundings show skinny CAPE profiles with TPW anomalies in excess of 200 percent (blended total TPWs), so healthy hourly rainfall amounts are forecast. We upgraded SW France to a level 1 due to better BL moisture/CAPE overlap into the evening/overnight hours, and a disorganized cluster of slow moving storms spreads NE, bringing local bursts of heavy rain and gusty winds (cold pool dependant). The main concern remains a spotty flash flood threat with healthy hourly rainfall rates.

Further N/NW, agile convection occurs along a confluent band of BL winds and slow moving nocturnal thunderstorms are forecast. Bad timing with lowered CAPE preclude an upgrade but a few heavy downpours are still possible over W-CNTRL to NW France during the night.

... E Mediterranean ...

Persistent upper troughing keeps thunderstorm risk alive over offshore and costal areas. The airmass is worked over with modest mid-level lapse rates and dried BL due to persistent trajectories off mainland Turkey towards the E Mediterranean. Still plenty of CAPE exists for numerous healhty updrafts with a local heavy rain and tornado risk.