Storm Forecast
Valid: Mon 06 Oct 2025 06:00 to Tue 07 Oct 2025 06:00 UTC
Issued: Sun 05 Oct 2025 10:14
Forecaster: TUSCHY

A level 2 was issued for parts of W Turkey mainly for excessive rain.

A level 2 was issued for SE Bulgaria mainly for excessive rain.

A level 1 surrounds both level 2 with a similar hazard but lowered probabilities. In addition, organized convection is also accompanied by some hail, severe gusts, heavy rain and a coastal tornado event.

SYNOPSIS

A strong anticyclone over SW/W Europe builds N and creates a stout ridge pattern with another anticyclone over the Barents/Kara sea. The downstream response will be a digging and deepening upper trough, which starts to cut-off from the waning westerlies. The resulting potent cut-off drops towards SE Europe with 500 hPa geopotential height percentile rankings in the 1-2 % range, so shy above monthly records. This development induces a broad LL vortex atop the Aegean Sea and adjacent areas, which lifts NE betimes on a slow pace. Interaction of this cut-off with the still dominant positive SST anomalies and attendant strong dynamics plus slow proper movement raise concerns for more excessive rain in this area - probably also in already affected areas from the past event a few days ago.

DISCUSSION

... Aegean Sea and surroundings like Greece, W-Turkey into SE Bulgaria ...

As the upper low approaches from the NW, a plume of moist and unstable air advects into an evolving warm sector over the highlighted area. The axis of highest moisture shifts towards the E Aegean Sea until the evening and further E during the overnight hours.

Until noon we expect numerous organized thunderstorms W of Greece atop the Ionian Sea in 500-1000 J/kg MUCAPE and 20 m/s DLS. Organized multicells and a few supercells pose all kind of hazards, including some hail (despite meager lapse rates), isolated severe gusts, heavy rain and an isolated tornado. This activity also affects far SW Greece into the Sea of Crete before winding down during the afternoon from W to E. Spotty 80 l/qm/12h are not ruled out over the W Peloponnese.

During the late afternoon into the overnight hours, falling MSLP atop the Aegean Sea enlarges hodographs (especially the lower parts), indicative of improving conditions for training convection along the coastal areas of W-Turkey (with impressive/rather unidirectional 0-3 km shear and DLS atop). Repeated CI is forecast and we expect swaths of 100-200 l/qm in less than 12h along the W coast of Turkey. Flash flooding is certainly possible on a local scale with a significant event not ruled out and hence a level 2 upgrade was performed. Coastal activity with more surface based thunderstorms also poses a gust and isolated tornado risk.

For SE Bulgaria, where extreme rainfall amounts with significant and deadly flash flooding occurred a few days ago, signals for high QPF amounts are once again present. The airmass atop the far SW Black Sea is less humid and unstable compared to the past event, but with lowering pressure to the S, another round of persistent onshore flow is forecast especially during the overnight hours. If we can get a persistent confluent low tropospheric wind field pointing into the coastal areas of SE Bulgaria we could see another round of training coastal convection with 12h rainfall amounts in the 100-250 l/qm range (as advertized by a few models). Strong SR inflow into evolving clusters certainly favors slow moving clusters. Due to the more stable stratification, this event could occur without embedded thunderstorm activity, which should keep the rainfall peaks lower compared to the past event (with isolated amounts in excess of 400 l/qm). Still we issued a low probability thunderstorm area with a level 2, which was added mainly due to the combination of high vulnerability and expected impact due to potential high rainfall amounts. Uncertainties with this event remain elevated due to the still vague development of the broad LL depression atop the Aegean Sea (e.g. where exactly the dominant LL vortex will finally materialize).

... Other lightning areas ...

We added a high probability lightning area for the offshore areas just W of the Irbe Strait into the W Gulf of Finland. A persistent and quasi-stationary convergence zone poses a risk of repeated but short-lived thunderstorm activity with a low-end waterspout risk. Heavy rain is possible along coastal areas but not worth a level 1 upgrade.