Extended Forecast
Valid: Sat 21 Jun 2025 06:00 to Sun 22 Jun 2025 06:00 UTC
Issued: Thu 19 Jun 2025 16:19
Forecaster: TUSCHY

A level 2 was issued for parts of NW Italy mainly for damaging gusts.

A level 1 surrounds the level 2 for hail (isolated large), strong to severe gusts and heavy rain.

A level 1 was issued for parts of Spain mainly for severe gusts and some hail.

A level 1 was issued for parts of UK into Scotland mainly for hail, strong gusts and heavy rain. An isolated tornado event is possible.

A level 1 was issued for parts of far S Italy mainly for hail, strong gusts and heavy rain on a local scale.

A level 1 was issued for parts of Greece mainly for some hail, strong gusts and heavy rain on a local scale.

SYNOPSIS

There is not much change to the rather static wave pattern over Europe. An anomalous strong ridge remains in place from SW to CNTRL Europe while expanding further N towards the Norwegian Sea before drifting E a bit during the forecast. This ridge gets framed by two troughs, one over the far NE Atlantic and another one over Scandinavia into Russia. The Russian trough sees numerous lower amplitude waves, circling the steering vortex over the S Barents Sea. Not much moisture advection is yet forecast, which limits overall severe and thunderstorm risk in this area.

Of more interest is the NE Atlantic trough, where parts of its energy drops S and evolves into a cut-off just W of Portugal. In the meantime, a strong cyclonic vortex just S of Iceland shifts E and induces a constant drift of the ridge axis from the Germany Bay E towards Denmark/Germany. This shift of the wave pattern results in a brisk SW-erly flow regime over parts of the UK.

A broad warm sector encompasses most of SW into NW Europe with a gradually eastbound moving cold front mainly affecting NW Europe during the forecast.

Dust advection should not be an issue as WCB inflow area remains far W of Morocco/Algeria, where weak winds prevail.

NWP gudiance is more or less on track regarding timing and strength of the main troughs/fronts, so confidence in the evolving pattern is robust for now.

DISCUSSION

... UK to Scotland ...

As usual with a SWODY 2 forecast, lingering finescaled uncertainties exist, but given the current rather stable NWP suite, confidence in organized DMC activity for the mentioned area is increasing.

The open warm sector features at least temporal diabatic heating during the day, offering deeper mixed BL conditions with LCLs aoa 2km AGL. It remains unclear, how much elevated convection could spread into the warm sector as SW-erly flow with embedded impulses works its way towards NW Europe. Even with passing elevated convection, WAA induced warming with at least some sunshine should push BL temperatures in the upper twenties. Lingering capping issues in the 850 hPa layer should prevent more surface based CI until the afternoon however. Still, further NWP data needs to be monitored closely for increased chances of isolated open warm sector convection over N-England, where cap remains weaker. Either near surface based CI or a gradual shift from elevated to more surface based CI is possible.

The main focus however resides along the cold front, which structures over W Scotland into Wales, where BL moisture pooling occurs. Some model discrepancies regarding BL moisture quality and effective EML/BL moisture overlap exist with GFS staying the most capped model, whereas ICON/EZ show more aggressive solutions. Combining all the data, we expect MUCAPE in the 1000-1500 J/kg range (regionally higher values possible) with intense shear along the frontal zone (EZ offering 0-3 km and 0-6 km shear in excess of 20 m/s). However most models right now indicate lingering cap issues and this highlights that this event could be steered heavily by the nowcast. E.g. onshore areas next to the Liverpool to Luce Bay with positive SST anomalies of 1-3 K could see additional BL moisture advection with adequate BL moisture for uncapped conditions. If this verifies, we could see a few supercells with all kind of hazards including a regionally enhanced tornado risk with up to 30 kt 0-2km SR inflow (e.g. Liverpool/Manchester and further N).

Otherwise expect an evolving evening/overnight severe risk in the level 1 area from SW to NE with organized multicells and a few supercells but with mentioned cap issues. Some hail, strong gusts and heavy rain are all forecast.

For now a broad level 1 was issued due to ongoing uncertainties regarding BL moisture magnitude, cap strength and prefrontal elevated convection. In case of a regional swath of near surface based activity during the evening hours, a local level 2 upgrade could be considered, inlcuding a tornado risk.

... NW Italy ...

An upper-level wave crosses NW Italy to the SE during the day, where MUCAPE in the 1000-2000 J/kg waits for CI. Despite some issues with the strength of the wave (with some models diverting more energy E towards Poland instead of taking it straight S towards Italy), enough mid/upper-level cooling is forecast for a very active day regarding DMC activity.

Scattered to widespread CI is forecast along the orography. Initially stationary convection poses a hail to large hail, excessive rainfall and strong to severe downburst threat. Betimes, convection moves off the orography and towards the lowlands while growing upscale into clusters. A well mixed BL with effective evaporative cooling but also lots of precipitation load should assist in rapidly growing/deepening cold pools and S/SE ward pushing clusters pose a risk of severe to damaging gusts with hail and heavy rain.
We expanded the level 1 area also far SE along the N Apennines to account for some clustered activity that far S.

Despite the long forecast range and some issues with the upper wave, a rather homogeneous signal for a convective-driven wind event is present to add a small level 2 area. Further modifications of the level areas may be needed.

Beyond sunset, convection weakens with strengthening cap onshore and offshore.

... NE Sicily to Calabria ...

The E-ward departing and gradually dissolving upper low leaves behind weakly capped 1500-2500 J/kg MUCAPE in a weak shear environment. Isolated CI along the orography or near merging sea breeze fronts is forecast. Intense updrafts may bring a temporal hail and very heavy rainfall risk on a local scale (next to a strong downburst event). Otherwise, a warming trend behind the cut-off/wave should suppress further activity away from the mentioned areas. A small level 1 should cover that risk.

... Spain ...

A plume of hot and deeply mixed airmass affects most of Iberia as LCLs soar aoa 3 to 3.5 km AGL. Strong insolation should assist in exceeding the convective temperature during the afternoon along the orography. Despite the arid and hot airmass, BL moisture remains noteworthy with up to 10C more inland and 10 to 20C when approaching the coasts. Positive SST anomalies of 2.5K over the S Bay of Biscay and 3-4K over the far W Mediterranean insert additional moisture into the onshore advecting marine layer. Hence we see inland MUCAPE aoa 1000 J/kg with higher but mostly capped MUCAPE towards the coasts.

IPV data has no hint at any passing wave within the mid-level flow but with a gradual decrease in thickness from the W, isolated to scattered CI is possible. High based convection with that amount of CAPE poses a severe downburst risk with any more intense cell. Some hail is also possible. We issued a wind-driven level 1 for the area with the most DMC activity although the actual severe risk will be rather localized (despite some temporal clustering indeed occurs).

During the night, an approaching impulse from the SW could support more CI on the isolated scale with some hail issues.

... S Greece ...

Up to 1000 J/kg MUCAPE but weak shear support scattered thunderstorms with isolated instances of severe (hail, wind and rain). A local upgrade was performded to cover a few robust updrafts as ICON and EZ inidcate spots of up to 1500 J/kg MUCAPE. Any severe risk is short-lived and ends during the evening.

... S Finland ...

This area could see some split-front convection during peak heating, which affects far S Finland into the Gulf of Finland. Right now, CAPE remains very weak including some uncertainties about the exact vertical structure of the front, so no level area was added. 15 m/s DLS and a mixed BL may support a few gusts with the stonger convection.