Storm Forecast
Valid: Tue 12 May 2026 06:00 to Wed 13 May 2026 06:00 UTC
Issued: Mon 11 May 2026 10:53
Forecaster: TUSCHY
A level 2 was issued across parts of SE Romania, Bulgaria into NE Greece and NW Turkey mainly for large to very large hail, severe gusts and regionally enhanced for heavy rain.
A level 1 surrounds the level 2 for similar hazards with lowered probabilities. In addition, a regionally enhanced tornado risk exists (e.g. Slovenia/far NE Italy during the morning).
A level 1 was issued for NE Spain mainly for hail, gusts and heavy rain.
A level 1 was issued for parts of W Russia mainly for hail and gusts.
SYNOPSIS
A blocking anticyclone is placed over the NE North Atlantic/N-Africa and both steer a longwave trough into CNTRL Europe. This through gets sheared apart as jet phasing occurs in its S quadrant and it acquires a negative tilt from E-CNTRL into SE Europe. During the night, a new impulse of low geopotential heights approaches from NW Europe and re-charges another longwave trough over CNTRL Europe for the following days.
At lower levels, a wavy boundary runs from NE towards E-CNTRL Europe before bending W towards the N Adriatic Sea. A more diffuse boundary extends towards NE Spain with only marginal S movement betimes. More fronts approach NW Europe during the forecast period but marginal moisture content precludes more substantial thunderstorm activity.
DISCUSSION
... NE Spain towards the NW Mediterranean ...
The passage of a short wave, coupled with cyclonic mid/upper flow and placed in the left exit of a 110 kt H3 jet create a favorable environment for scattered thunderstorms during the forecast. Cooling mid-levels atop modest low-tropospheric moisture assists in 400-800 J/kg MUCAPE onshore, increasing to more than 1 kJ/kg offshore. EFI MUCAPE highlights the offshore areas with anomalous values, whereas EFI CAPE/shear keeps the focus along the coast of NE Spain.
Shear/CAPE is adequate for multicells and isolated supercells in the level area with 2-3 cm hail, strong gusts and bursts of heavy rain forecast. The hail risk may temporarily increase just offshore but overall a cooling footprint of the Mistral event should turn offshore convection more elevated betimes with a decreasing severe risk.
... SE Europe ...
In response to the approaching upper trough, mid-levels cool atop seasonable low-tropospheric moisture (slightly above background climatology for Romania into Bulgaria). The net result is a broad warm sector with MUCAPE in the 1000-2000 J/kg range and with adequate DLS (around 15 m/s) for a mix of organized multicells/a few supercells.
Forecast soundings show rather thick mid-level CAPE profiles with high ELs and modest sub-0C CAPE, so large to isolated very large hail will be one risk. The other risk will be severe gusts as convection moves into more than 800 J/kg DCAPE and 8K/km lapse rates in the lowest 3 km. A level 2 was added, where vertical shear profile/hodograph structure favors more discrete convection, which occurs over most of Bulgaria into SE Romania.
The level 2 was expanded into far NE Greece with similar background conditions but also deep into NW Turkey, where shear increases from the W during the day. The setup offers up to 2000 J/kg MUCAPE with elongated /rather straight hodographs, so large to isolated very large hail and severe gusts remain the main hazard. The complex orography however also adds a growing heavy rain threat betimes with clustering convection. Far NW Turkey is a bit uncertain reagarding CI however.
... Slovenia to Croatia and N-Bosnia and Herzegovina into Serbia ...
The passing mid/upper level trough axis features a strong Q vector couplet, pointing to abundant synoptic-scale lift for scattered CI. This lift meets a moist airmass downshear, advected from the CNTRL Mediterranean in a brisk SW-erly flow regime.
Organized morning convection occurs over Slovenia/far NE Italy with a few supercells well possible. Hail in the 2-3 cm range is possible next to strong gusts and a temporal enhanced tornado threat (thanks to the moisture trajectories direct off the N Adriatic Sea). This activity clusters betimes and a progressive MCS event with embedded supercells is forecast to spread over N Bosnia and Herzegovina into Serbia before weakening further E. Probably storm-intern dynamics (like dominant RIJ position) decide where the highest gust risk resides with ongoing NWP spread. Hence no level 2 upgrade was performed but confined swaths of level 2 conditions are possible (e.g. MCS driven gusts).
A broad level 1 surrounds the level 2 area with overlap of strengthening shear and modest CAPE. Hail, gusts, heavy rain and an isolated tornado are possible with variable probabilistic maxima.
... E Poland, W Ukraine into Belarus ...
A plume of moist/unstable air spreads N with diurnal MUCAPE peaks up to 1kJ/kg on a regional scale. Weak shear precludes organized DMC activity with some hail, heavy rain and isolated gusts the main risk. A low-end tornado is not ruled out in this moist BL airmass but depends on storm scale to mesoscale processes.
... Parts of Germany ...
A low CAPE/high shear setup evolves along the SW fringe of the upper trough. EL height peaks at 3.5 km AGL, so intense mid/upper flow remains more or less untouched. The main risk will be graupel/small hail and strong gusts with strongest updrafts/shallow mesocyclones in case of some deviating convection.
... Parts of W Russia ...
Modest MUCAPE/shear assist in a few semi-organized multicells with isolated hail and gusts.
