Storm Forecast
Valid: Wed 05 Nov 2025 06:00 to Thu 06 Nov 2025 06:00 UTC
Issued: Tue 04 Nov 2025 15:55
Forecaster: TUSCHY

A level 1 was issued for parts of Greece and surrounding areas mainly for heavy to locally excessive rain. A coastal/offshore waterspout risk exists on an isolated scale.

A level 1 was issued for parts of Spain/Portugal for a tornado, hail, severe wind gust and heavy rain risk. A strong tornado event cannot be ruled out.

SYNOPSIS

Extensive blocking persists over most of Europe. Embedded in positive height anomalies is a broad/weak upper trough over SE Europe with two dipoles - one over Romania and another one atop the Ionian Sea/S of Greece.
A negative tilted trough crosses SW Europe during the forecast and spreads towards the W Mediterranean during the overnight hours.

DISCUSSION

... Parts of Greece and offshore areas ...

During the start of the forecast period the upper low will be analyzed SW of Greece, which then drifts SE during the following hours. IFS-ENS (of MSLP) has numerous crowded ensemble members S of Greece, which tend to merge into one dominant vortex towards the night/over Crete.

A moist/unstable airmass advects towards S/E Greece with weak BL flow, which turns dominant northeasterly during the day along the backside of the departing vortex. This BL flow regime pushes storm motions within local hodographs to near zero and quasi-stationary/back-building convection poses an excessive rain threat on a local scale, also with isolated waterspout events along the coasts. QPFs offer local peaks in excess of 200 l/qm within a few hours and flash flooding is possible on a local scale. A significant event is not ruled out, if such an event occurs over a town.

...Portugal and Spain...

A complex forecast evolves during the passage of the upper trough and attendant cold front. A strong prefrontal warm jet advects a very moist/subtropical airmass (e.g. atop the Gulf of Cadiz with more than 2 K positive SST anomalies) towards Portugal/S Spain, which turns unstable during the day with occasional diurnal heating. MUCAPE resides in the 400-800 J/kg range well onshore with more than 1000 J/kg over S Portugal/SW-Spain.

Impressive shear accompanies the upper trough with DLS in the 30 m/s, 0-3 km shear in the 20-30 m/s range and LL shear up to 15 m/s on a regional scale.

Organized convection is certainly possible with a straight hodograph/CAPE overlap (lowered SRH but robust LLCAPE) and further improving overlap of thermodynamics/kinematics as diurnal heating sets in (also improving SRH/CAPE overlap). A lowered angle of shear vectors/frontal motion vector could suppress discrete activity a bit with favored clustering (also enhanced by splitting storms) but there certainly exists a risk of at least a few semi-discrete cells ahead of the cold front and/or embedded within line segments.

We expect a rapid increase of a tornado/heavy rain and severe gust risk from 06Z onwards over Portugal, as convection spreads E/NE. The main focus for a tornado threat arises with any more discrete cell or near line breaks. The risk spreads E especially towards SW Spain, where best SBCAPE exists during the day. This causes an ongoing tornado/wind/heavy rain and hail risk.
Further N (towards CNTRL Spain), a few fast moving rotating thunderstorms are also possible with a tornado/severe wind gust and isolated hail threat.

Unclear amount of diabatic heating, dominant storm mode and onshore decay of CAPE preclude a focused level 2 for now. However any more discrete storm could produce a strong tornado event from S/CNTRL Portugal to SW/CNTRL Spain.

During the night, the severe risk also increases over NE Spain and a line with strong to severe thunderstorm shifts E. A few embedded supercells could produce isolated hail/strong gusts and a tornado or two mainly along the coastal areas. Heavy rain becomes another issue, although moving convection should keep the final rainfall amounts within the level 1 threshold.

Please keep in mind that a non-thundery heavy rain risk over N-Portugal and a strong/severe gradient wind risk over mountainous areas and over NW Spain exist but this won't be covered by Estofex.