Storm Forecast
Valid: Sun 13 Jul 2025 06:00 to Mon 14 Jul 2025 06:00 UTC
Issued: Sat 12 Jul 2025 20:31
Forecaster: TUSCHY

A level 2 was isued for far NW Russia into Estonia mainly for large hail, severe gusts and very heavy rain. An isolated tornado event is possible.

A level 2 was issued for parts of the Tyrrhenian Sea for large to very large hail, heavy rain, severe gusts and a few tornadoes.

A level 2 was issued for parts of far NW Italy mainly for excessive rain and an isolated tornado event.

A Level 1 areas surround all level 2 area for similar hazards but with lowered probabilities.

A level 1 was issued for parts of E France to Hungary mainly for isolated hail, gusts, heavy rain and a tornado or two.

A level 1 was issued from the Netherlands E towards Poland for an heavy rain risk, which turns more to isolated hail/gusts, heavy rain and a tornado or two towards Poland.

A level 1 was issued for parts of Ireland mainly for heavy rain and isolated hail.

A level 1 was issued for far NE Algeria into NW Tunisia mainly for large hail and severe downburst gusts.

SYNOPSIS

Positive geopotential heights increase mainly over Scandinavia in response to impressive high-latitude blocking for this time of year. This anticyclone connects to strong subtropical anticyclones over the Mediterranean in the form of broad ridging over far E Europe into far W Russia.

South of this Scandinavian blocking anticylone, a zonally aligned channel of lowered geopotential heights extends from the NE Atlantic towards CNTRL and SW Europe. Numerous more or less defined cut-offs are embedded within this channel and bring unsettled conditions to various places. In addition, numerous low-amplitude waves circle the main steering vortices and cross the W/CNTRL Mediterranean east.

An extensive frontal boundary runs from S Sweden E towards W Russland, where it bends south. The airmass E of this boundary is very unstable and ready for DMC activity.

DISCUSSION

... Tyrrhenian Sea to the Ligurian Sea ...

A pronounced IPV maximum moves into the area of interest from the W and interacts with a very unstable and strongly sheared airmass. Point source soundings from offshore areas show MUCAPE up to 2000 J/kg with 20 m/s shear in the lowest 3 km and 6 km. Forecast hodographs feature long and slightly curved signatures with a risk of precipitation venting into the track of any storm. Hence a growing cluster seems most likely with semi-discrete supercells along its southern fringe. This is mainly an offshore threat with an all kind hazard risk forecast: (very) large hail, severe gusts, very heavy rain and mesocyclonic tornadoes especially in the path of any supercell with near surface based inflow. A mix of ensemble data and deterministic runs was used for placing the offshore level 2. The level 1 was expanded towards the coasts but decreasing CAPE and increasing cap issues should lower the severe risk somewhat.

W-CNTRL Italy is a bit uncertain as subsidence along the cluster's periphery could indeed lower the general severe risk but this area (NW or Rome) has to be monitored for some coastal convection with an attendant severe risk.

In addition, another focus for organized convection evolves near the Ligurian Sea and coastal areas. Either we see another growing cluster in this area, which moves slowly E/SE during the day (like IFS is forecasting), or we see slow moving and training convection along the coast. If no clustered offshore convection evolves, the coastal storms could be accompanied by extreme rainfall rates with an unstable and very moist inflow from the SE, which lowers the final storm motion. Rainfall rates up to 80-100 l/qm/h on a local scale are possible with multi-hour rainfall amounts of 150-300 l/qm not ruled out. This would bring flash flood issues on a local scale. The main limiting parameter is the overall weak inflow as otherwise the stage is set for healthy rainfall events. Beside that risk, a few coastal tornadoes and some hail with strong gusts are also forecast (especially it we get a cluster going). Despite mixed signals in model guidance we push this into the level 2 category mainly due to the rain threat.

NE Algeria/N Tunisia will be on the southern fringe of this IPV maximum, so CI is very uncertain with not much reflection in latest data. Still an isolated event is possible and decent shear/CAPE would support a hail and severe gust threat. A small level 1 was added.

... Far W Russia into Estonia ...

Once again we see a favorable setup for organized convection along/ahead of the wavy frontal boundary. Similar to yesterday, another mid-level wave is forecast to ride the front to the N/NW and even some transient LL pressure fall is not ruled out (but not well relfected in latest IFS-ENS data).

From the start of this forecst onwards, a growing cluster along the border of Belarus/W Russia tracks N, and later on NW towards Estonia. This convection has access to 1500-3000 J/kg MUCAPE with roughly 10 m/s DLS and 0-3 km shear. Despite modest shear, internal storm dynamics with healthy cold pool activity should support a growing bow echo with swaths of strong to severe gusts next to large hail and an isolated tornado risk mainly with more discrete activity along the cluster's fringes.

As the cluster approaches Estonia and the Gulf of Finland/SE Finland from the SE, the concern for very heavy to extreme rainfall amounts increases as convection becomes better aligned within the background flow and experiences constant inflow from the very unstable wamr sector. Ensemble data has strong signals for healthy and flash flood producing rainfall amounts with isolated peaks in excess of 100 l/qm/12h not ruled out. However a big uncertainty is, if the cold pool is strong enough to push this MCS rapdily N/NW, which would lower the mentioned rainfall threat. A third solution is that we see a growing and well defined MCV event with this cluster, which would result in enhanced rainfall concern along its fringes, which could also affect N /E Latvia. For now we kept the levels rather broad.

During the night, a large nocturnal cluster races W towards the CNTRL Baltic Sea into E Sweden with heavy rain, some hail and gusts. We expanded the level 1 far W.

Further E into W Russia, an extensive warm sector offers 1500-2500 weakly capped MUCAPE with very weak shear values. Numerous initiating cells pose an hail threat and in case of merging cells, very large hail is not ruled out. Betimes, erratic moving small clusters bring all kind of hazards more on a local scale. No real focus for more concentrated severe is forecast, so a broad level 1 should cover this event.

... SE Austria into NW Hungary but also NE Italy ...

A belt of brisk westerlies overspreads the area of interest with 500-1000 J/kg MUCAPE. Initiating splitting cells pose some hail and gust risk before growing upscale into a progressive cluster mainly from SE Austria into Hungary. Storms enter a well mixed BL airmass with a growing gust threat into NW Hungary, but the overall severity should stay below a level 2.

... Rest of Austria to Switzerland and far E France but also far S Germany ...

Growing MUCAPE during the day with somehwat strengthening low to mid-level flow create a broad swath for a few more organized updrafts. MUCAPE in the 500-1000 J/kg range interacts with up to 15 m/s DLS, so numerous multicells and isolated supercells bring some hail, gust and heavy rain issues. Even an isolated tornado event is not ruled out with better LLCAPE from NW Switzerland into SW Germany. This activity weakens beyond sunset.

... N Germany into Poland ...

The slowly westward shifting cyclonic vortex sparks isolated to scattered thunderstorms over N/NE into E-CNTRL Germany. For convection next to the vortex' center (far N/NE Germany), the troposphere seems to be worked over by active convection from the previous day next to somewhat more stable BL inflow from the NE. Slow moving convection poses an isolated heavy rain risk. An isolated short tornado/funnel event over NE Germany is not ruled out with temporal diabatic heating and somehwat enhanced LL CAPE.

Further S, towards E-CNTRL Germany, better CAPE and 10-15 m/s DLS support a few multicells with some hail and gust risk next to isolated heavy rain. Further E into Poland and far NE Czechia, MUCAPE increases towards 10-15 m/s with WAA induced hodograph curvature. A mix of multicells and a few supercells is forecast with some hail, gusts and heavy rain issues. An isolated tornado event is possible with lowered LCLs and a more unstable 0-3 km layer.

We pushed the level 1 far N over most of N Poland to account for slow moving and partially clustered convection with heavy rain and an isolated tornado risk.

We also extended the level 1 into the Netherlands for a few heavy rain reports with slow moving convection.

... Parts of Ireland ...

Ahead of a gradually approaching cold front and upper trough, a growing cluster of thunderstorms is forecst during the afternoon onwards. A sharp shear gradient exists within a plume of 400-800 J/kg effective MUCAPE as DLS increases from NE to SW from 10 to 20 m/s. A mix of multicells and transient supercells is forecast, which grow upscale while moving offshore. Heavy rain will be the main risk despite some hail and gusts.