Storm Forecast
Valid: Mon 15 Sep 2025 06:00 to Tue 16 Sep 2025 06:00 UTC
Issued: Sun 14 Sep 2025 13:00
Forecaster: TUSCHY
A level 1 was issued across far SW Denmark into extreme N Germany mainly for locally excessive rain and an isolated tornado risk along the coasts/offshore.
A level 1 was issued for parts of E-Germany into Czechia and W Poland mainly for some hail, gusts and an isolated tornado.
A level 1 was issued for parts of the Alps mainly for some gusts, hail and heavy rain.
SYNOPSIS
A broad cyclonic vortex over NW Europe steers numerous low amplitude waves to the E/NE, which are embedded in a brisk flow regime. This gyre moves from Scotland to S Norway and pushes a cold front deep into CNTRL Europe. A shrinking prefrontal warm sector from NE Germany into Poland serves as main focus for DMC activity.
Quiescent conditions persist over most of the Mediterranean/S Europe.
DISCUSSION
... Far SW Denmark into extreme N Germany ...
Situated S of the NEward moving upper vortex, a long westerly fetch atop the warm German Bay (positive SST anomalies between 1 to 2 K) points into the level 1 area. Forecast profiles show long lasting unidirectional shear conditions, which support the growth into organized shower streets with embedded thunderstorm activity. Abundant LL CAPE is available for LL vortex stretching atop mesoscale convergence zones and a few tornadoes/waterspouts are forecast. In addition, healthy convection affects the same spots during the day with 24h rainfall amounts in the 40-80 l/qm range possible. Strong near BL flow also adds a gust risk to this convective activity, especially beyond midnight.
... Parts of Germany into W Poland and N Czechia ...
An eastward progressing cold front serves as focus for some DMC activity. Placed beneath a diffluent and neutral to convergent upper flow regime, the main forcing seems to emerge from low/mid tropospheric positive thickness advection during the passage of a weak positive IPV maximum beside the confluent fow regime along the cold front itself. It remains uncertain, too, how strong CAA affects the boundary and how long it takes for evolving updrafts to fight against drier environmental air above 700 hPa.
Next to those issues, NWP guidance remains optimistic in at least isolated CI within the level 1 area around noon onwards. ID2 forecast soundings show an impressive CAPE/shear space of 800-1200 J/kg MUCAPE overlapping with 20 m/s DLS and 20-25 m/s 0-3 km shear. Forecast hodographs reveal WAA driven curved profiles with good SR inflow into evolving updrafts. LCL hover around 600-800 m AGL with some LL CAPE supply especially along the German/Polish border. Similar conditions are forecast by EZ with a somewhat less aggressive scenario offered by GFS.
Expect initial struggeling but betimes merging updrafts, which then acquire enough vertical/horizontal extent to turn into organized multicells and a few supercells. The main issue seems to be some hail and gust, although an isolated tornado event cannot be ruled out with any longer-lived supercell. The highest risk seem to evolve over far E/NE Germany into W Poland.
Further S, weaker forcing should keep CI limited to a few storms. In case we see updraft organization, a favorable CAPE shear space exists for longer lived rotating updrafts and small bow echoes with some hail, gust and isolated tornado issues.
... Parts of the Alps ...
The arriving cold front sparks numerous thunderstorms along the Alps, which could temporarily acquire some organization with gusts, heavy rain and some hail before weakening starts as they leave the Alpine crest to the E.
... Lightning areas over E-CNTRL Europe ...
We could see a few high density lightning tracks exiting the currently highlighted 50 % lightning areas in case long-lived/rotating updrafts evolve and shift E. It remains very uncertain however, how many thunderstorms will do so and where they progress E, so we decided to not issue an extensive 50% lightning area for now (e.g. E Poland into Slovakia) .
