Storm Forecast
Valid: Mon 19 May 2025 06:00 to Tue 20 May 2025 06:00 UTC
Issued: Sun 18 May 2025 19:32
Forecaster: TUSCHY
A level 2 was issued for SW France and the Spanish/French border mainly for excessive rain and also for large hail.
A level 1 surrounds that level 2 for similar hazards. In addition we expect an augmented tornado risk just N of the Pyrenees.
A level 1 was issued for parts of the Dinaric Alps mainly for severe gusts and hail but also for a low-end tornado risk.
A level 1 was issued for parts of S Ireland mainly for a few tornado events and heavy rain.
A level 1 was issued for parts of Romania into Moldova mainly for severe gusts and isolated hail.
SYNOPSIS
As a blocking anticyclone persists over far NW Europe/Iceland, a progressive trough passage occurs over SE Europe. This feature pushes an active cold front E/SE, which will be accompanied by organized convection.
A zonally moving and weakening upper trough crosses far N Spain and the Pyrenees E before entering the Gulf of Lion area. It is accompanied by lowering MSLP and becomes the main focus for DMC activity.
DISCUSSION
... SW France to NE Spain ...
The eastbound moving trough crosses the Pyrenees. A basal 60 -75 kt mid/upper jet places strong upper divergence over SW France during prime time for initiation. This feature includes some better mid/upper moisture from the tropics, which approaches from the SE. The net result will be deep moist profiles with MUCAPE in the 500-1000 J/kg range. Overall a favorable setup for organized convection evolves.
Some CI occurs over W-CNTRL France before noon with slow moving and gradually intensifying convection. Some guidance keeps this convection going with upscale growth into a long-lived MCS, which crosses parts of the N Massif Central to the NE. This makes sense as airmass ahead of the convection becomes unstable with 10-15 m/s DLS. Strong to isolated severe gusts, hail and heavy rain become the main hazard.
The main show however occurs around noon onwards in the level 2 area and surrounding level 1. Widespread CI is forecast from SW to NE. Initiating cells organize rapidly admit 15-20 m/s DLS and numerous multicells/supercells are forecast. Hodographs in this region show signals for mature HP cells as wind speeds at upper levels lower rapidly. Modest storm motion of this structuring cells points to an heavy rain threat and extreme rainfall rates are certainly possible especially with merging cells. Flash flooding is possible on a regional scale.
Despite modest mid-level CAPE, isolated large hail is also forecast as deep/strong SRH3 rich inflow into updrafts is forecast with relaxed LL shear.
The tornado risk is lowered due to meager LL lapse rates/LL CAPE but regional LCLs in the 500-700 m range could certainly add an isolated event. A more solid tornado risk exists just N of the Pyrenees/around and S of Toulouse, where deeper LL moisture overlaps with strongly looped hodographs and LLCAPE in excess of 200 J/kg. A strong event is not ruled out.
In addition cold pool driven swaths of severe gusts are possible as bowig segments evolve. Upscale growth into an MCV is possible, but diminishing CAPE after sunset casts uncertainties regarding how well organized this vortex becomes. However it could enhance nocturnal rain on a regional scale.
During the overnight hours, convection weakens, before a nocturnal V-shaped (but progressive) MCS event evolves next to the coastal areas of S-France. This activity shifts E until 06Z. Heavy rain and isolated hail will be the main risk for that activity next to a waterspout risk along the coast.
Some nocturnal and elevated convection occurs over parts of the W-CNTRL Mediterranean but should stay sub-severe until 06Z. Isolated hail cannot be ruled out.
... N/E Romania into Moldova ...
A progressive cold front sparks numerous thunderstorms during noon/afternoon, which organize into numerous broken lines of storms. Straight/elongated hodographs with ample DLS and 10-15 m/s 0-3 km shear point to splitting cells with isolated hail and scattered severe gusts the main hazard. The latter risk may be more widespread over NE Romania into Moldova, where BL airmass is better mixed. This activity moves offshore until the evening hours and weakens in response to a strengthening cap.
... Dinaric Alps...
A similar CAPE/shear setup evolves in this area with weak/modest CAPE (400-800 J/kg MUCAPE) but strong shear at mid to upper levels (20 m/s DLS and 15 m/s 0-3 km shear). CI occurs around noon along the orography and thunderstorms cross this fetch of unstable air for some hours to the SE. This is enough for numerous longer-lived multicells and isolated splitting supercells with hail and strong to isolated severe gusts. The hail risk will be hampered by rather limited mid-level CAPE. An isolated tornado event is not ruled out with lowered LCLs during late afternoon into the evening.The activity weakens around sunset at CAPE becomes marginal at best.
... S Ireland ...
A level 1 for an augmented funnel/short-lived tornado and flash flood risk was issued for the noon/afternoon hours. The background environment offers decent LL CAPE along a slow moving LL confluence zone for a few spin-ups especially during the more discrete phase along any LL convergence zone. Betimes, clustering convection poses an heavy rain risk with isolated flash flooding possible. The risk decays after sunset.
