Storm Forecast
Valid: Fri 04 Sep 2026 06:00 to Sat 05 Sep 2026 06:00 UTC
Issued: Thu 03 Sep 2026 18:34
Forecaster: TUSCHY

A level 2 was issued for parts of E-CNTRL/NE Germany into W Poland mainly for severe gusts and an isolated tornado risk.

A level 1 surrounds the level 2 for similar hazards with lowered probabilities. In addition, there is a confined risk of heavy rain.

A level 1 was issued for Denmark to the S Baltic Sea mainly for severe gusts, some hail and an isolated tornado.

A level 1 was issued for parts of SW Russia and surroundings mainly for hail and gusts.

SYNOPSIS and DISCUSSION

*** Update ***

Some changes became necessary for this SWODY1. The wave is better captured in NWP guidance, pushing the wave E over N Germany around noon with 60kt at H85. Of interest will be the inflection point of this wave and its backside, where convection deviates more from the intense LL shear vectors. That's the time, when we could see a SE ward shifting LEWP over NE Germany within an impressive shear background. CAPE is marginal at best but we talk about 25 m/s 0-3 km shear and weak 0-3 km CAPE, also highlighted by better gust peaks in CAMs. In addition, line breaks will be prone to rotation with extreme SRH along this LEWP and a tornado risk is present. Again, marginal CAPE dampens this risk and confidence in this level 2 upgrade is not yet really high, but we go with the current NWP trend, pointing towards stronger deviating convection from the LL shear vectors.

Behind that wave, the S ward sagging cold front turns more active during the late afternoon into the overnight hours with enhanced thunderstorm activity forecast as MUCAPE increases into the 250-500 J/kg range. There are signals of a weak trailing wave along this cold front, which crosses E-CNTRL Germany during this time and this improves LL shear once again. BL stabilization is seen in NWP guidance, but strong moisture adevection and WAA dampens that effect, so we cannot exclude near surface based thunderstorms. Point source soundings show 30 m/s 0-3 km shear, 40 m/s DLS and 300 m2/s2 SRH3, which is intense shear. Nowcast is certainly needed to determine the chance for tornadoes. Right now, weak gust signals reflect the more elevated nature, but little BL modification is needed. Any surface based storm could produce a strong tornado and hence we expanded the level 2 south. Again, we need to monitor CAPE magnitude as current CAPE guidance resides more at the lower edge with diffuse UH track signals but strong vorticity tracks. Hence current level 2 upgrade is also rather aggressive, but latest trend points to an increasing risk in NWP gudiance.

The western part of the level 1 covers more the heavy rain risk as 60kt LL flow advects anomalous moist air into elevated convection along the wave's tip.

We kept the level 1 over Denmark and further E. Splitting cells are forecast with straight hodographs and deviating cells could rotate in an intense shear background. Low LCLs also point to a tornado risk as BL winds back a bit onshore within augmented 0-3km CAPE. Otherwise some hail and strong to severe gust are forecast. This will be an afternoon/evening risk. The tornado risk exists also outside of the level 2 but with lowered confidence

We downgraded the Baltic States and Belarus as CAPE/shear weakened and we upgraded a small area over far SW Russia and surroundings for a severe risk (hail/gusts).

We also added a higher lightning probability for Portugal to account for more aggressive overnight convection (elevated). Some hail and heavy rain is possible.

Otherwise, please refer to the SWODY2 text for more detail.

*** Previous discussion ***

A still highly uncertain risk of organized convection exists with a passing and gradually evolving wave, which crosses N Germany/N Poland E during the daytime hours, before deepening into a closed vortex over the Baltic States during the night.

What bears watching is the highly anomalous nature of the parameter space, which converges along the wave's path.

Impressive energy transfer/zonal wave flux occurs over N Europe into a Scandinavian trough with anomalous low heights from Scandinavia to Scotland. This energy transfer meets an anomalous intense subtropical ridge, which runs from Spain to S France. In-between, an impressive 2-3 sigma deviation of mid/upper level winds is forecast with jet core winds in excess of 140 kt at H25/3. This deep/polward sloped frontal zone also offers H7 winds in excess of 50 kt, which creates anomalies in excess of 2 sigma to the background climatology.

This dynamic regime meets an IVT maximum in excess of 1300 kg/m/s, which highlights not only very effective moisture advection, but also an impressive magnitude of moisture with TPWs in the 35-45 mm range, spreading over Benelux/N Germany E. In fact, this moisture plume could be accompanied by a diabatic Rossby wave (DRW), which then turns into our progressive wave.

Right now the only missing ingredient seems to be enough upper dynamics in form of a sharp IPV maximum. The shown scenario favors a broad and gradually sharpening trough during the forecast period, sparking BL vortex development late in this forecast over N Poland into the Baltic States. A more rapid positive PV imprint in the BL is still possible however and is shown in some GEFS/IFS members. This evolving depression seems to be a complex interaction of a lee cyclone E of Norway with the leftover of the DRW. IFS-ENS also reveals an ongoing spread with a broad member cloud of MSLP minima in the 1000-1010 hPa range at 12Z over N Germany to the S Baltic Sea.

Details dictate how much instability build-up will occur along the wave's path. Meager mid-level lapse rates occur (due to the tropical background of this potential DRW and tropospheric airmass), but robust moisture advection increases probabilities for at least skinny CAPE profiles.

We most likely see some heavy rain issues along the wave's tip, as 55kt at H85 feed anomalous moisture into elevated (probably non-thundery) convection. This risk increases if we see a passing wave and is currently maximized somewhere over N Germany in NWP guidance.

Otherwise, the gust risk over Belgium/the Netherlands to Germany will be the main issue, also highlighted by the EFI gust forecast with values in the 0.9-1 range, including a positive SOT over N Germany. Any convective component could induce a severe gust threat especially for convective elements, which deviate more from the 20-30 m/s 3km shear vector, which is out from the west. This is possible N of the wave's tip with cooling mid-levels but also if we get a closed vortex/warm sector, which bends the cold front more SW-NE. A broken LEWP along the leading edge of the wave is forecast right now with strong to severe gust. Line segments/breaks will be prone to isolated tornado activity in extreme shear, as point source soundings show skinny CAPE with 22 m/s LL shear, 30 m/s 0-3km shear and SRH 1 and 3km in excess of 350-400 m2/s2. If we get only somewhat better CAPE in this shear setup, we would also need to add an isolated strong tornado risk.

Right now we just added a broad level 1 area to highlight a general augmented risk. Major discrepancies of the wave's path and development stage could decrease overall severe risk but also push it locally into a significant stage, especially in case of a more aggressive LL vortex spin up (which seems less likely right now due to the mentioned delayed upper IPV approach and which is supported by a current weakening trend f.ex. in latest ICON runs). In the end, we could also see a rather inactive wave passage with a severe corridor to its N, covering N Germany into Denmark.

This event bears close monitoring in further runs and a regional upgrade/downgrade will be possible.

Another level 1 was added for the Baltic States into Belarus for a lead wave, which affects this area during the daytime hours. Shear is weaker, but low LCLs and some noteworthy SRH induce an isolated tornado risk.

Portugal and SW Spain could see a nocturnal risk of a few elevated thunderstorms in response to an approaching upper trough. Some hail would be the main issue next to a few gusts. Right now, EPS data only reveals some signals in EPS maxima, so not much confidence for CI right now (although NWP guidance has problems with elevated CI and overall pattern could favor more aggressive CI during the night).