Storm Forecast
Valid: Wed 30 Apr 2025 06:00 to Thu 01 May 2025 06:00 UTC
Issued: Tue 29 Apr 2025 20:35
Forecaster: TUSCHY

A level 2 was issued for the SE coast of Turkey mainly for large hail, excessive rain and a strong tornado risk. A few severe gust events are also possible.

A level 1 surrounds the level 2 for similar hazards with lower probabilities. Towards the W, the heavy rain and isolated tornado risk becomes more dominant.

A level 1 was issued for parts of Latvia and far S Estonia mainly for an isolated tornado and hail/gust risk.

A level 1 was issued for far NW Spain mainly for isolated tornadoes, heavy rain and some hail.

A level 1 was issued for parts of Portugal mainly for isolated tornadoes and heavy rain.

SYNOPSIS

A broad anticyclone remains centered over most of W/CNTRL Europe and gets framed by two strong cut-offs. One is placed atop the Herodotus Basin E/SE of Crete and this vortex lifts leisurely N during the forecast, while approaching the coast of S Turkey during the end of the day. At the surface a broad LL vortex evolves just W of Israel while lifting N just W of Syria before approaching Cyprus during the night. A weakening trend is then underway.

Another cut-off W of Portugal continues to amplify as another jet max circles its W/SW fringe. During the night, a weakening trend is forecast as this vortex begins to fill while starting to lift N/NE. At the surface, a vigorous vortex drifts S/SE with standard deviations to the background climatology in the -4 range, pointing to an unsual strong/deep vortex for that time of year. BL response causes a long fetch of E-erlies over the far W Mediterranean merging into a levante event in the Strait of Gibraltar - at least initially before an eastward surging cold front ushers in from the W with a rapid wind shift to the W/SW.

Numerous synoptic fronts circle the blocking high pressure area but remain displaced from the best moisture/instability. The only exceptions will be a slowly E-ward shifting cold front over Portugal/Spain, which turns quasi-stationary betimes and starts to wave and a progressive occlusion over Latvia.

DISCUSSION

... Portugal and Spain ...

Ahead of the slowly eastward shifting cold front, low-tropospheric winds from the S/SE advect some moisture onshore. Persistent easterlies create a moisture plume offshore with mixed BL mixing ratios in the 8-9 g/kg range. This moisture however remains rather shallow with forecast soundings indicating a depth of 50-100 hPa above ground. Hence this onshore advecting moisture is vulnerable to mixing admit strong diurnal heating.

The main focus for CI resides along the cold front, where moisture deepens next to enhanced mid-tropospheric moisture along the front itself. In response to steepening mid-level lapse rates over the orography, this moisture input is adequate for some elevated MUCAPE. Effective hodographs show rather straight profiles in this layer and enough shear for some longer-lived updrafts with some small hail. An isolated large hail event cannot be ruled out in case of a lowered inversion and regionally enhanced lapse rates. As the front becomes stationary during the night, repeated shower/thunderstorm passage could cause isolated flash flood issues. Overall no focused severe risk is expected to justify an upgrade for most of Spain.

One exception is far NW Spain, where near surface based CI is forecast in a CAPE/shear space, which supports a few multicells/isolated supercells. Any cell, which rides along a onshore moving sea breeze could see a small window of opportunity for a low-end tornado risk. Clustering convection also brings heavy rain and isolated hail.

Another level 1 upgrade was performed over parts of S/CNTRL Portugal. Behind the departing cold front, a moist marine airmass advects ashore and destabilizes due to some diurnal heating. Shear is adequate for multicells with heavy rain and a low-end tornado risk. NWP guidance differs a bit regarding magnitude of MUCAPE well inland but most models show enough CAPE within the level 1 area for a few organized storms. This risk diminishes beyond sunset.

We were rather aggressive in expanding the lightning areas E towards the Balearic Islands to account for a few elevated offshore thunderstorms during the night in response to growing MUCAPE with improving moisture input from the Mediterranean. Despite some graupel/small hail and locally heavy rain, nothing severe is anticipated for now.

... S Turkey ...

A regional and substantial upgrade was performed to account for higher confidence in numerous severe events during the forecast.

During the daytime hours, expect scattered thunderstorms along the orography with mainly non-severe activity due to meager CAPE. An exception exists for any updraft, which roots into the unstable marine layer along the coast with MUCAPE in the 500-1000 J/kg range. Hail, isolated large and locally heavy rain would be the main issue.

During the night however, conditions for organized DMC activity improve as the structuring depression draws moisture N towards Cyprus while the mid/upper vortex lifts towards the far SW coast of Turkey.
The first focus is the area next to the upper vortex, which affects most of the SW/S coast of Turkey. Persistent onshore flow overlaps with improving mid-level lapse rates from W to E, so expect MUCAPE to increase to the E with peak values in the 1-1.5 kJ/kg range N/NE of Cyprus. DLS starts near zero next to the vortex' center near the Rhodes/Antalya Basin. Here the main risk will be slow moving/clustering convection with heavy/isolated excessive rain and a few waterspouts (especially next to Rhodes).
Further E, cap increases admit a warming lower troposphere, but there exists a confined swath with robust MUCAPE (up to 1 kJ/kg) and near zero CIN - probably along the coast of Mersin and later-on further E. Here, training and onshore moving convection poses a risk fo large hail, heavy to locally excessive rain and strong to severe gusts. A mesocyclonic waterspout/tornado event along the coast is possible. Backbuilding towards Cyprus is not ruled out and that's why we added this area into the level 1. During the end of the forecast, a similar CAPE/shear space exists over the Gulf of Alexandretta with EZ pointing to an augmented nocturnal tornado risk along the coasts.

A level 2 upgrade was performed, where confidence exists for numerous severe events including a chance for a strong tornado along the coast.

Finally, SE/E of Cyprus, an extreme LL shear environment evolves in response to the structuring LL vortex, but a deepening cap should prevent CI for most of the day. During the night, numerous thunderstorms evolve along the coast of W Syria with isolated hail and heavy rain.

... Latvia and far S Estonia ...

A structuring LL vortex shifts E/SE during the day and is accompanied by a progressive occlusion. A dry slot approaches this front from the W during the day and assists in low-end CAPE build-up. ICON remains more aggressive than other models but in general a few thunderstorms are possible during the afternoon into the evening hours. A rather classic low CAPE-high shear setup is forecast and there is a chance for a few fast moving low topped supercells. Curved hodographs and low LCLs point to an isolated tornado risk next to strong gusts. A small level 1 was added for this risk, which abates after sunset.