Storm Forecast
Valid: Sat 14 Jun 2025 06:00 to Sun 15 Jun 2025 06:00 UTC
Issued: Fri 13 Jun 2025 20:08
Forecaster: TUSCHY

A level 2 was issued for parts of France mainly for large to very large hail, severe gusts and heavy rain.

A level 2 was issued for NE Spain mainly for large to very large hail, severe downbursts and heavy rain.

A level 2 was issued for NW Italy mainly for large to very large hail, severe downbursts and very heavy rain.

Numerous level 1 areas surround those level 2 areas with similar hazards but lower probabilities.

A level 1 was issued for S Turkey mainly for large hail and severe gusts.

SYNOPSIS

A stagnant large scale wave pattern persists also during this forecast period. A robust blocking ridge over CNTRL Europe starts a slow weakening trend while creeping east a bit. This ridge gets framed by two extensive upper vortices, one centered over far W Russia with a progressive lower amplitude wave diving S towards the Black Sea with an ongoing amplification trend of the growing vortex. The second vortex is placed over Ireland and lifts gradually NE towards Scotland while weakening. This vortex induces diffuse surface pressure fall over the English Channel, which then lifts N towards England. EZ-ENS member spread remains extensive (zonally), so the final track and the depression's intensity remain still uncertain (roughly 5 hPa member spread at 12Z with members spreading NE from Ireland well into the German Bay). This depression pushes a cold front from NW France E a bit with a rather tight clustering in the ensemble regarding placement at 12Z, which is roughly from extreme W Belgium S/SW towards CNTRL France. Upstream of the cold front is a weak 1 to 2 hPa MSLP trough, which acts as a weak prefrontal confluence zone. This affects the Netherlands into NW/W Germany during peak heating.

Elsewhere no synoptic-scale front impacts today's thunderstorm forecast.

Regarding dust issues we do not expect any serious impacts as low/mid tropospheric flow at the inflow of the WCB was weak to modest at best, which gets reflected also f.ex. in the integrated water vapor transport forecasts, which place the inflow area way N towards France/Spain. Dust load forecasts show modest values, which affect E France into Switzerland and SW Germany.


DISCUSSION

... NE Spain to France into Germany and Benelux ...

A plume of rich moisture with PWATs in the upper 90 percentile rank (but not a record level) covers most of W into W-CNTRL Europe with readings in the 30 to 40 mm range. Advected layered PW data indicates two source regions with one source region along the subtropical offshore area of the far E Atlantic. The other one is a northward advecting plume of high mid/upper level moisture from the tropics, which advects N from Algeria towards France. LL modification atop the 3K (plus) SST anomaly over the W Mediterranean only increases moisture input. Prefrontal BL moisture offers impressive LL mixed mixing ratio values locally in excess of 15 g/kg.
A strong thermal ridge with H85 temperature readings in the upper tens to lower twenties is placed beneath the ridge and remains displaced of the cold front and the high prefrontal moisture values. Still, some overlap occurs and pushes ICAPE in the solid 1500-2500 J/kg range with regional higher peaks not ruled out.

The SW-erly flow is rather smooth with not much wave activity forecast. IPV data reveals some weak waves, affecting the highlighted area but the intensity of those waves remains uncertain (e.g. convective amplification by yesterday's convection is possible, which could boost any wave's intensity to what is currently depticted in NWP data). Latest Q vector forecast indicates a weak wave crossing NW Germany around noon to the N with stronger signals of more waves thereafter over France. No jet maximum intersection with the prefrontal airmass is anticipated although we see a temporal increase at mid-levels along the 12Z wave over W/NW Germany (also affecting SW Germany) and an overall improving background shear environment along the front itself during the day. During the forecast with see the best shear setup along the western CAPE plume (France to Benelux and far NW/W Germany) with a gradual decrease to the E.

There will be various reasons for regional CI either due to a passing wave, due to diabatic heating or a vanishing cap. In addition, internal storm dynamics dictate a regionally enhanced severe risk, which is very hard to pinpoint.

We split the broad area into the following sub-regions for CI:

Far NE France into Benelux and W/NW Germany will see CI along the periphery of the passing wave. Lingering morning convection (probably in form of a temporarily weakening MCS or smaller clusters) over far NE France pushes into Belgium, where increasingly uncapped 2000 J/kg MUCAPE awaits the convection. It remains a bit uncertain, if some elevated convection evolves ahead of the main activity or if the morning convection weakens into a broad area of numerous showers/isolated thunderstorms, which would lower LL mixing ratios significantly on a regional scale due to effective evaporative cooling. This sceario would limit re-strengthening of ongoing morning/forenoon convection as otherwise rapid re-intensification would be possible. Right now we expect a decreased/ more isolated severe risk over Benelux during the daytime hours but any more discrete cell, ingesting high CAPE and growing in roughly 15 m/s DLS could organize into a multicell/isolated HP supercell with hail (isolated large), excessive rain and a few strong downburst gusts. Upscale growth into a small cluster is possible.

Noon onwards, the E ward pushing outflow interacts with the prefrontal confluence zone and the local orography over W/NW Germany. Isolated CI is forecast and small-scale upscale growth into a longer lived cluster is not ruled out, dependant on convection coverage. A similar CAPE/shear space due to the wave's enhancement of the background wind is forecast and any cell could produce hail (isolated large one with 3 to 5 cm in diameter despite some melting beneath 2km LCL heights), excessive rain and strong to severe downdraft gusts (with ID2 ensemble indicating slim probs. for a few bft 11 gusts in case of a growing cold pool). Especially if the wave experiences some convective amplification, we could see a growing MCS risk fo NW Germany but uncertainties for this remain high for now.

Over SW Germany, very strong diabatic heating results in effective BL mixing and CAMs show numerous eastward surging drylines on the mesoscale. These interact with weakly capped 2000 J/kg MUCAPE and the added BL convergence could spark an isolated thunderstorm around Upper Swabia and furthr E. A temporal severe risk would exist as any storm most likely outruns the LL mesoscale support rather fast. If it remains stapled longer in the mentioned CAPE with 10 m/s DLS, we could see a longer-lived event with a confined swath of severe.

The mentioned storm activity either weakens rapidly or more gradually in case of better cold pool dynamics with rather chaotic storm motions.

Due to the mentioned uncertainties no level 2 upgrade seems reasonable. Still clustered severe reports are well possible along the path of any cold pool driven activity and especially NW Germany has to be monitored closely for a growing MCS event.

... France to CNTRL Germany ....

The best CAPE shear space exist over CNTRL to NE France, where 15-20 m/s DLS overlap (at least partially) with 2000-2500 J/kg MUCAPE. CI occurs over the Massif Central and to the N/NE. Intense updrafts with very large hail (larger than 5 cm in diameter well possible), severe downdrafts and excessive rain are forecast during the late afternoon into the evening hours.

As convection pushes E/NE into the high CAPE environment, an upscale growing cluster is forecast. During the overnight hours, improving upper divergence beneath a structuring right entrance region of a 90kt H3 jet maximum combined with healthy cold pool dynamics support a progressive MCS event with swaths of strong to severe gusts and hail into NE France. Betimes (after sunset), increasing CIN should push LFC beyond 2km AGL and this trend should induce a weakening of the surface gusts. MUCAPE in excess of 1000 J/kg is still enough for an ongoing hail and heay rain issue as this MCS spreads into CNTRL Germany until 06Z. We cannot rule out a growing MCV event, which pushes into NW Germany with continuous re-development of storms along its SE fringe (CNTRL Germany). If such an upscale growth occurs, we could see a dominant heavy rain risk along the NW fringe of the MCV and a lingering hail risk from SW into CNTRL Germany.

Parts of the mentioned area were upgraded to a level 2 mainly for swaths of severe hail/gusts.

... SW into CNTRL France ...

Another area for a progressive MCS event evolves over SW France along the stalling cold front. Overnight CI is forecast over SW France and this activity moves into 1500 J/kg MUCAPE and modest 0-3 km/DLS. Swaths of hail and severe gusts spread E towards the Massif Central area until 06Z. The level 2 was expanded into the area of interest.

... Spain ...

Strong diabatic heating creates a diurnal driven thermal low, which advects a moist airmass onshore towards CNTRL/NE Spain. Along the orography, this moisture advects beneath steep mid-level lapse rates, which creates up to 2500 J/kg MUCAPE. DLS of 15-20 m/s is more than enough for organized convection with large to very large hail, severe downdrafts an heavy rain. A drying BL results in a decreasing thunderstorm activity beyond the evening hours. A confined level 2 was added for the highest hail threat.

... N Italy ...

Rich BL moisture with 2m dewpoints in the lower twenties and 500 m mixing ratios up to 15 g/kg beneath the African EML create weakly capped 2500-4000 J/kg MUCAPE during the day. CI along the orography but also near a passing (weak) wave should spark numerous intense thunderstorms. Despite DLS below 10 m/s, initiating storms will pose a large hail threat with very large hail in excess of 5 cm possible. Very heavy rain and severe downdrafts are also forecast. As convection moves off the orgraphy a rapidly increasing cap should induce a gradual weakening trend. Due to the risk of numerous extreme events, another level 2 was added. We expanded the level 2 far S towards the S Piemonte, where ID2 has up to 5000 J/kg weakly capped MUCAPE along the orography. Only weak signals for CI exist (even in ensemble field data) but any growing updraft could become severe in a short amount of time and a low confident level 2 was added there.

... SE Europe towards SE Russia ...

Modest CAPE and weak shear precludes organized thunderstorms even towards E Belarus, where shear improves (with 200-300 J/kg MUCAPE).

A local level 1 upgrade was performed over S Turkey for a few large hail and severe gust reports.