Storm Forecast
Valid: Sun 17 Aug 2025 06:00 to Mon 18 Aug 2025 06:00 UTC
Issued: Sat 16 Aug 2025 20:41
Forecaster: PISTOTNIK

A level 1 is issued for Corsica, parts of Italy and the Balkans for severe convective wind gusts, excessive convective rain and large hail.

A level 1 is issued for parts of Spain mainly for severe convective wind gusts.

SYNOPSIS

A cyclone slowly moves from the Baltic region into adjacent Russia. In its wake, cooler and rather dry air flows southward into E and central Europe. Slightly lower 500 hPa geopotential and northerly surface winds also spread into the Balkans and the central Mediterranean region, easing the latest heatwave to some degree.
Further upstream, a subtropic ridge extends from Iberia to the North Sea, bringing stable and warm weather into W Europe, and still extreme heat into SW France and Iberia.

DISCUSSION

... Spain, Italy to the Balkans and Romania ...

The long anticyclonic period has left an extensive plume of hot air with steep lapse rates across the entire southern third of Europe. Low-level moisture is rather scarce in inland areas, owing to little evaporation and deep vertical mixing, and keeps CAPE mostly limited to values below 800 J/kg. Much richer low-level moisture and CAPE well in excess of 1000 J/kg are in place in coastal and offshore areas (e.g., almost 3000 J/kg were sampled by the Sat 12 UTC Ajaccio sounding), but the maritime boundary layer remains strongly capped.
In the absence of noteworthy synoptic lift, isolated to scattered, daytime-driven thunderstorms will mostly be tied to orographic features. With weak vertical wind shear and a rather limited storm coverage, severe weather occurrence should remain rather isolated. The strongest pulse storms can produce severe downbursts, excessive rain and large hail on very isolated scales. These hazards are relatively highest in areas where maritime moisture might be fed up into upslope and upvalley circulations, most notably in Corsica and central Italy, but this scenario is too uncertain to upgrade these areas to a level 2.
In the particularly dry and CAPE-deprived environment of inland Spain, severe downbursts remain the only noteworthy hazard. They may even occur without any precipitation reaching the ground. In addition, lightning strikes could ignite further wildfires (not explicitly covered by our hazard level scheme).

... Eastern Alps to the Ukraine an W Russia ...

A narrow belt of enhanced low-level moisture, and hence a few hundred J/kg CAPE, are also present just ahead of the weak cold front that inches southward. Vertical wind shear is weak in central Europe before it increases to 15 (20) m/s across the 0-3 (0-6 km) layer over the Ukraine, providing an environment for some better organized storms there.
Current thinking is that synoptic subsidence in the broad cold air advection regime should keep thunderstorm coverage very limited. A few storms may still be left over from the previous night in Austria and Hungary, but are not expected to intensify considerably in the course of the day. Over the Ukraine and W Russia, convective initiation could largely or even completely fail until the evening. Later on, storms detaching from the Carpathian mountains in Romania could travel some distance eastward in the evening and overnight, in case their track can favourably coincide with a sea breeze front propagating inland from the Black Sea. Limited CAPE and relaxing vertical wind shear keep the severe weather hazards too low for a level 1.

... W coast of Latvia, Lithuania and Kaliningrad ...

In the northerly flow on the back side of the departing cyclone, a long fetch of polar air over the comparably warm Baltic Sea could create just enough CAPE for the formation of one or two flow-parallel bands of "lake effect" showers towards the end of the forecast period. Localized excessive rain along with an isolated tornado are not ruled out. No lightning or level 1 area seem necessary for now due to the short time window and uncertain scenario.