Storm Forecast
Valid: Sun 20 Apr 2025 06:00 to Mon 21 Apr 2025 06:00 UTC
Issued: Sat 19 Apr 2025 10:21
Forecaster: TUSCHY
A level 1 was issued across the Genoa area mainly for heavy rain and an isolated/coastal tornado risk.
A level 1 was issued for parts of N-Italy mainly for some hail and gust events but mainly for heavy rain.
A level 1 was issued for SE France mainly for isolated heavy rain.
A level 1 was issued for parts of Germany with a mix of heavy rain and some hail/gusts.
A level 1 was issued for NE Algeria and N Tunisia mainly for large hail and severe gusts.
SYNOPSIS
A blocking anticyclone over E Europe/Russia precludes any eastward progress of Atlantic troughs. They start a gradual cut-off process over W Europe before splitting apart into numerous pieces. The main impulse drops SE towards the Mediterranean, whereas numerous low-amplitude waves affect W/CNTRL Europe.
A broad/filling low pressure area over France pushes an occluding frontal boundary towards Germany, which serves as main focus for CI. Some WCB convection occurs over parts of CNTRL/N Italy with some severe possible down towards Tunisia.
DISCUSSION
... CNTRL to N Italy ...
The WCB is characterized by a meridionally aligned fetch of modest isentropic lift with more stratiform rain during the start of the day. Around noon onwards, conditions for embedded DMC activity improve although placing any hot spots remains tough.
We added a confined level 1 to the Genoa area for some training thunderstorm activity until the afternoon hours. An isolated tornado event is possible.
We also added a broad level 1 along/N of the N-Apennines, where some diurnal heating assists in MUCAPE in the 500-1000 J/kg range. A few organized multicells/supercells are possible with hail and strong to isolated severe gusts. The main risk however becomes heavy rain with temporal training along the orography. Convection either outruns CAPE betimes or turns more elevated during the evening onwards.
... S-CNTRL France ...
A broad cyclonic circulatzion covers most of France and pushes a marine airmass E. Diurnal heating assists in weak/modest MUCAPE during the day and thunderstorms are forecast roughly between the E-Pyrenees and Paris.
Between Toulouse and Montpellier, a temporal line-up of thunderstorms (N-S) is forecast as a moist airmass from the Mediterranean advects NW and into ongoing thunderstorms. Weak DLS and clustering may cause some flash flood issues on an isolated scale and a confined level 1 was added.
Further N, isolated to scattered thunderstorms evolve beyond noon with isolated hail but mainly gust issues due to a well mixed BL. Isolated nature of activity precludes an upgrade for now.
Next to the vortex' center (along its E fringe), a plume of somehwat better LLCAPE may add a low-end funnel/short-lived tornado risk on a very isolated scale. That's not enough for any upgrade. Convection decays beyond sunset.
... S/CNTRL Germany ...
A NE ward shifting occluding front slows down during the day. Accompanying better prefrontal BL moisture overlaps with a weak Alpine EML, so expect a belt of 400-800 J/kg MUCAPE over CNTRL Germany.
DLS increases from 10 m/s to 15 m/s (W to E) with rather short and straight hodographs to the W. A messy mode of splitting and clustering cells is forecast. Initiating and merging cells pose a local flash flood risk, which is maximied along the orography. Isolated hail and gusts are also possible. Betimes, clustering convection shifts N with a dominant heavy rainfall risk, before weakening into the overnight hours.
Towards Thuringia and SW Saxony, 15 m/s DLS may also assist in a few better organized multicells and some updraft rotation. This could locally enhance the hail and gust risk.
Further S (S-CNTRL into SE Germany), an eastward pushing cold front/pressure wave interacts with a rather mixed airmass with lowered BL moisture due to subsiding air N of the Alps. In addition, somewhat more anticyclonic flow aloft may suppress CI a bit. Nevertheless, EPS keeps some CI alive both along the front itself but also along the orography. DLS is very strong (in excess of 20 m/s) and may mix drier environmental air into growing updrafts. Hence ECAPE may be lowered compared to MUCAPE forecasts. If an updraft can survive for some time, a mixed BL may cause strong to isolated severe gusts and some hail issues. We upgraded also to a level 1, but kept lightning probabilities low to highlight ongoing uncertainties regarding magnitude of CI.
... NE Algeria to N Tunisia ...
Scattered elevated thunderstorms are forecast ahead of an eastward moving cold front. 15 m/s DLS is forecast with effective shear a bit lower depending on the vertical extent of the cap. Nevertheless a few robust updrafts are forecast, which bring isolated large hail and numerous severe downburst events.
