Storm Forecast
Valid: Wed 24 Jun 2026 06:00 to Thu 25 Jun 2026 06:00 UTC
Issued: Tue 23 Jun 2026 17:09
Forecaster: TUSCHY
A level 2 was issued for large to very large hail for parts of Portugal and NW Spain.
A level 1 surrounds the level 2 for similar hazards but also for heavy rain and severe gusts.
A level 1 was issued for parts of the Balkans, parts of Italy and SE France mainly for isolated hail, gusts and heavy rain.
A level 1 was issued for far S UK mainly for isolated hail, gusts and heavy rain.
SYNOPSIS
No change on the synoptic-scale with an extensive and record-breaking anticyclone still placed over CNTRL into NW Europe. A hot airmass spreads towards NW Europe and is about to release its full force/impact also over UK.
A cut-off just W of Portugal gets re-charged and one piece of energy rotates N over Portugal and into far NW Spain. In the meantime, a diffuse/broad trough covers Tunisia E towards Turkey and then N into NW Russia.
Despite the cold front passage over Portugal, no front-driven DMC activity is forecast. Most of the CI will occur along the orography, near mesoscale boundaries or along the fringes of weak (partially convectively enhanced) positive PV anomalies. In addition, extreme surface heat over France could also add some CI probabilties despite record-breaking warm of the lower troposphere. Once again nowcast trends need to be monitored closely for CI as mesoscale dynamics dictate most of the activity.
DISCUSSION
... SE France, parts of Italy and the Balkans ...
Another day with sattered diurnal driven convection. Intense updrafts are forecast with MUCAPE rising up to 2000 J/kg or more.
Near zero DLS over the Balkans favors initial stationary thunderstorms, which become mobile by internal outflow dynamics betimes. Heavy to locally excessive rain, some hail and gusts will be the main hazard.
Placed beneath a weak NE-erly steering flow, converging and upslope moving sea breeze fronts over W Italy initiate numerous intense thunderstorms with hail, gusts and heavy to excessive rain. Isolated large hail is possible.
The same for the western Alps with scattered diurnal driven thunderstorms along the orography. Same CAPE magnitude and weak to modest DLS (around 10 m/s) support a hail, gust and heavy to isolated excessive rainfall risk. A few extreme rainfall events are not ruled out along the orography with flash flooding possible (ID2-EPS with locally peaks up to 70 mm/h).
... N Portugal and NW Spain ...
The northward lifting vorticity lobe induces CI along the orography but CI is also expected along the north-/northeastward surging cold front during the evening hours onwards.
Main issue will be the prefrontal advection of a hot/dry airmass from CNTRL Spain towards the NW, which causes capped conditions during the day (excluding isolated mountain storms). However, abundant lift should establish a NW-SE aligned cluster of thunderstorms during the evening onwards, which affects the level areas.
Capped 2500 J/kg MUCAPE with non-effective DLS in excess of 25 m/s are present with effective shear probably cut in half (dependant on how deep updrafts root into the lower troposphere). Nevertheless, elevated supercells with large hail are certainly possible with an hail diameter in excess of 5 cm forecast and a confined hail-driven level 2 was added. Heavy rain is also forecast and probably maximized in the level 2 area, where temporal back-building convection is forecast. Despite the capping issues, a few strong to severe downburst events are possible, especially in the deeper mixed BL more inland.
... W/SW France ...
Similar to yesterday, numerous high-based thunderstorms with isolated strong to severe downbursts are possible (LCL height in the 3.5-4 km AGL range with DCAPE in excess of 1500 J/kg on a local scale). NWP guidance is once again very diffuse regarding magnitude of CI, so no level area was issued for now. Mesoscale dictates, if a more clustered severe event could evolve (e.g. a temporal upscale growing cluster with severe gusts).
... S UK and Ireland ...
An extremely moist and hot airmass resides over S UK with capped MUCAPE in the 3000-4500 J/kg range.
Still rising heights, strong cap (for most places) and no real hint of any disturbance make CI quite unlikely. EPS data supports that idea with ICON-EPS f.ex. showing nil prob. in its maximum.
However, there remains the concern along the S coast of UK for an inland moving sea breeze front interaction with that CAPE-rich airmass to initiate a cell. In addition, GFS hints at a weak cyclonic circulation, which enters the English Channel from the W and could locally enhance coastal convergence. As CIN virtually erodes to near zero near the coast, CI cannot be ruled out completely despite entrainment concerns of growing updrafts into the very dry subsidence layer along the inversion.
A low confident level 1 was added as any longer-lived updraft would be able to produce large hail, severe gusts and heavy rain. Nowcast is once again needed for capturing any growing CI probabilities.
For Ireland, a passing wave during the evening into the overnight hours could add an isolated risk of elevated thunderstorms with some hail and locally heavy rain. Once again there is not much model support for that but we issued a lightning area for this conditional risk.
