Storm Forecast
Valid: Tue 22 Jul 2025 06:00 to Wed 23 Jul 2025 06:00 UTC
Issued: Mon 21 Jul 2025 13:49
Forecaster: TUSCHY

A level 2 was issued for Denmark and surroundings mainly for excessive rain.

A level 1 surrounds that level 2 for a similar hazard with lowered probabilities. An isolated tornado is possible.

A level 1 was issued fo parts of S-CNTRL Germany mainly for a few tornadoes.

A level 1 was issued for parts of SE Europe (Romania to Ukraine) mainly for large hail, gusts and heavy rain.

Numerous level 1 areas were added for SE Austria, NE Italy into far W Croatia and parts of Bosnia and Herzegovina mainly for isolated hail, gusts and heavy rain.

A level 1 was issued for far NW France mainly for heavy rain.

SYNOPSIS

Yet another round of blocking anticyclones, one placed between Greenland and Scandinavia and another one zonally shaped from the subtropical Atlantic towards the Mediterranean and Turkey/Middle East. In between those anomalies resides a zonally aligned channel with lowered geopotential heights including a restructuring vortex over Germany into NW Europe. Another upper low over W Russia opens up while drifting E.

Along the surface a long and wavy front runs from the Faroe Islands to S Norway/Sweden towards Belarus, Ukraine and bends back to the W towards the N Adriatic Sea. The same for the weakening upper low over W Russia, which has a weak surface imprint in form of a filling/eastward shifting depression, which frames a warm sector by an eastbound/northbound moving cold and warm front, respectively. These fronts play a crucial role for an active thunderstorm day over an extensive area from E Europe into Russia.

DISCUSSION

... Denmark and Germany ...

A filling and gradually N/NE ward lifting upper low steers a warm and moist airmass towards S-CNTRL Germany during the day. Despite meager mid-level lapse rates, we see streaks of modest MUCAPE build-up in the 200-400 MUCAPE range mainly from Rhineland Palatinate to N/CNTRL Bavaria. Forecast soundings show barely enough CAPE depth for sufficient riming but at least a low-end and short-lived thunderstorm event cannot be ruled out. Despite meager CAPE, the setup supports better organized shallow mesocyclones with 25kt 0-3 km westerly shear increasing to (non effective) 45 kt 0-6 km shear within a belt of broadly enhanced SRH and LCLs around 600 m AGL. Hence a few short-lived tornadoes with showers and spotty thunderstorms are possible next to a few stronger gusts and graupel. A local level 1 upgrade was performed mainly because some models at least show somewhat enhanced probs. for numerous healthy and longer-lived updrafts, which cross this rather favorable moist/sheared environment with persistent rotation signals in NWP guidance.

Further N over N-Germany, relaxing shear beneath the upper low induces slow moving convection with isolated bursts of heavy rain. An isolated funnel/short-lived tornado is possible with somewhat augmented LLCAPE. Of main interest is far NW/N Germany, where a weak westerly low/mid-tropospheric flow tuns easterly in the upper troposphere while increasing to 65kt. This not only takes the storm motion near the center of the hodograph but also results in westward venting of evolving precipitaion cores. This could result in very local but high QPF peaks with some models indicating spotty peaks of 60-90 l/qm/6h on a local scale (in a 30 mm PWAT environment). Due to the spotty nature of this risk a level 1 should be sufficient.

Further N towards Denmark a long-lasting heavy rain event is ongoing and continues during this forecast. A focused channel of low pressure with rich/deep moisture supports that more stratiform shaped rain event. However some MUCAPE is forecast, especially along the northern fringe of the low pressure channel, so convective elements increase rainfall rates on a local scale. Very impressive 24h rainfall amounts occur with 50-100 l/qm forcast by most models. Convective elements could even surpass these amounts on a local scale. Due to embedded thunderstorm activity, we issued level areas for this event (despite the mostly stratiform nature).

... Belarus, Ukraine towards Romania ...

The slow moving/quasi-stationary boundary from Denmark turns more progressive towards E/SE Europe in form of a progressive cold front. This boundary interacts with a quite unstable prefrontal airmass with MUCAPE in the 1500-2500 J/kg range. DLS below 10 m/s remains weak, so expect scattered to widespread slow moving pulsating thunderstorms with heavy rain, gusty winds and isolated hail. Despite meager shear, merging and broadening updrafts in more than 2000 J/kg MUCAPE should be enough for a few large hail reports. This risk is diven on the storm to mesoscale. ICON places the highest risk from far NE Romania into the CNTRL Ukraine, where we added a level 1. A few severe events are well possible outside of the level 1 but should stay too isolated for a more extensive upgrade.

... NE Italy to Slovenia into far W Croatia, SE Austria and Bosnia and Herzegovina into W Serbia ...

A brisk westerly flow regime with embedded weak waves impacts the mentioned area during the forecast. Rich BL moisture with 2m dewpoints in the upper tens to lower twenties converge near the N Adriatic Sea (SST anomaly +1.5K) and expands more inland during the day. MUCAPE resides in the 1000-1500 J/kg range with higher values, where BL moisture peaks. CI is spotty and probably bound to any moving moisture wind shift/convergence line but is also possible during the morning hours with somewhat enhanced convergence along the periphery of southward sagging diffuse cold front.

Any sustained updraft can organize thanks to 20-25 m/s DLS and a few splitting supercells with large hail, excessive rain and gusty winds are forecast. Any storm, which can tap into the rich marine airmass and ride a convergence zone could produce a tornado thanks to rich LLCAPE - especially during the morning hours. Thereafter, mixing pushes LCL to 1 km AGL, which hampers the overall risk.

Same for SE Austria, where a few organized thunderstorms ride the orography during the afternoon to the E/SE with some hail, gust and heavy rain issues.

Same for parts of Bosnia and Herzegovina into far W Serbia, where mountain convection could organize while moving off the orography and one or two longer-lived multicells/transient supercells with hail, gust and heavy rain are forecast.

... SE/E Spain ...

An onshore advecting rich marine airmass advects beneath enhanced mid-level lapse rates along the orography, which results in capped 1500-2500 J/kg MUCAPE. Rather dry mid-levels probably lower the effective CAPE however. The initial more anticyclonic curved mid/upper flow regime turns more cyclonic beyond noon, but NWP guidance remains reluctant regarding CI. Even ensemble data give only weak signals along the orography for isolated CI. Combined with lowered CAPE, no level area was added for now.

... NW France ...

An approaching upper trough sparks numerous nocturnal thunderstorms, which could approach the coastal area as multicells with DLS in excess of 15 m/s. Heavy rain will be the main issue.