Storm Forecast
Valid: Wed 07 Aug 2024 06:00 to Thu 08 Aug 2024 06:00 UTC
Issued: Tue 06 Aug 2024 16:21
Forecaster: TUSCHY

A level 2 was issued across parts of Emilia-Romagna into far S-Veneto and the Gulf of Venice mainly for severe gusts and heavy to isolated excessive rain.

A level 2 was issued in S Austria/W-Slovenia mainly for heavy to excessive rain.

A level 1 surrounds that level 2 for similar hazards but with lowered probabilities, including isolated large hail (which is also valid for the level 2 area). The German level 1 areas are mainly issued for isolated hail, heavy rain and strong gusts. A low-end tornado risk exists over W-CNTRL into SW Germany during the evening hours.

A level 1 was issued for parts of Denmark mainly for heavy rain on a local scale. A low-end/short-lived tornado risk exists.

A level 1 was issued for Moscow to the Smolenskaya/Kaluzhskaya/Tul'skaya oblasts mainly for heavy rain.

A level 1 was issued for Moray Firth, Orkney/Shetland Islands and the coast of SW Norway mainly for strong to isolated severe gusts.

SYNOPSIS

Overall we see a transition towards a more zonal flow regime over NW/W into CNTRL Europe. A progressive/weakening ridge over E-Germany shifts into Poland, whereas positive mid-level height anomalies persist over the Barents Sea, while rising heights overspread most of the Mediterranean (in response to the building zonal flow regime).

Steered by a filling but still potent low just SE of Iceland, a cold front pushes E/SE over W into CNTRL Europe. Ahead of this cold front, a convergence zone could play some role for pre-frontal CI.

DISCUSSION

... Germany to the Alps to Italy and Slovenia ...

For Germany:

The eastbound moving cold front with a prefrontal convergence zone will be affected by a fragmented upper trough, which causes numerous weak low-amplitude waves to impact the area of interest.

A lead impulse spreads thunderstorms from far E France into S Germany during the day with some strong to isolated severe gusts and hail mainly in Bavaria and a few heay rain events elsewhere. PWs up to 35 mm may cause some heavy rain issues especially with colliding convection but also in case of a transient MCV feature. The latter however is rather uncertain due to the overall disoganized nature of convection with 10 m/s DLS in roughly 1000 J/kg MUCAPE background. A level 1 was added.

Another focus for transient storm organisation evolves over N-CNTRL into NE Germany along the prefrontal convergence zone. 0-3 km shear increases to 10 m/s, so a few more organized storms could bring some heavy rain/hail and gusts. This area is a borderline low-end level 1 event.

Finally, a third wave with better shear (DLS 15 m/s and 0-3 km shear of 10 m/s) affects SW/ W-CNTRL Germany during the afternoon/evening hours. Modest lift and storm motion vectors placed normal to the frontal motion could cause a few more discrete storms and an isolated supercell event is possible. ID2 remains rather aggressive with this event, whereas other models keep this activity more isolated. Any stronger cell could produce isolated hail, strong gusts and heavy rain. A low-end tornado risk would exist over W-CNTRl Germany (RLP, Hessen, N-BW), where LCLs remain low. A level 1 was issued for this event.

During the night, convection shifts E and weakens.

For the Alps into Slovenia and Italy:

A more humid/unstable airmass resides over N Italy, where MUCAPE remains in the 2000-3000 J/kg range with decreasing values towards Slovenia. This airmass interacts with the approaching trough, respectively with an eastward moving low-amplitude wave, which breaks apart from the main trough.
CI occurs along the mountains and DLS at or below 10 m/s should support numerous intense updrafts, which could bring some hail with an isolated large event not ruled out, next to heavy rain and strong to severe downbursts. Interaction with the orography could support a few flash flood events on a local scale. We expanded the level 2 into S Austria/W-Slovenia to account for this rainfall risk.
Betimes, the activity builds away from the mountains into the weakly capped and very ustable airmass. Colliding outflow boundaries probably induce numerous growing clusters with heavy rain, isolated hail and an increasing wind gust threat, dependant on how healthy the cold pool becomes. We issued a level 2 for this area, where confidence in numerous severe events is the highest.

During the night, convection weakens with increasing CIN, but a strong outflow boundary with strong/severe gusts may surge far S over the Adriatic Sea. We kept this part of the event in a low thunder/level 1 combination in case of isolated CI along the boundary.

... Parts of Denmark ...

This area will see some diurnal heating ahead of the approaching front with some stronger updrafts during the cold front passage. A low-end level 1 was added for heavy rain on a local scale. If we get a more deviant storm going, a low-end/short-lived tornado risk is possible due to very low LCLs and some helical inflow.

... Moscow to the Smolenskaya/Kaluzhskaya/Tul'skaya oblast...

Placed beneath a stationary upper trough, scattered convection is forecast in a weakly capped/sheared environment. Slow moving storms bring heavy rain on the local scale, which caused this level 1 upgrade. This convection drifts slowly E during the night.

... Moray Firth, Orkney/Shetland Islands and the coast of SW Norway ...

Just S of the steering vortex, some mid-level drying atop a moist marine layer causes patches auf 400-700 J/kg SBCAPE. Background wind field is rather strong along the fringes of the strong vortex, so the main risk will be numerous strong to isolated severe gusts with the main risk during the late afternoon into the overnight hours. A low-end level 1 covers this threat. Strongest convection may also bring some (small) hail.