Storm Forecast
Valid: Mon 15 Apr 2024 06:00 to Tue 16 Apr 2024 06:00 UTC
Issued: Sun 14 Apr 2024 20:24
Forecaster: TUSCHY

A level 2 was issued for severe to damaging wind gusts across parts of S Slovakia/far N Hungary.

A level 1 was issued across SE UK into CNTRL Germany mainly for severe wind gusts and an isolated hail/tornado risk.

A level 1 was issued from the SE Germany/the Alps east into the Ukraine for swaths of large hail, severe wind gusts and an isolated tornado risk.

SYNOPSIS

Weak background momentum out of the subtropics and enhanced momentum along the midlatitudes (including a positive Arctic Oscillation) all support an ongoing low-latitude blocking event with positive height anomalies extending over most of S Europe. Two cut-offs meander deep in the south (in the 25-30N range) but play only an indirect/advective role for the European weather (e.g. backing the previous heat anomaly over most of S/CNTRL into E Europe).

Lower height anomalies over Scandinavia/S of Iceland face this belt of subtropical ridge and cause an extensive and anomalous intense upper jet configuration which runs from Ireland to Germany to Belarus.

Two depressions become the main foci for some convective activity with one moving from Scotland to N-Germany and a second one leaving Finland to the NE. Both features modulate an extensive frontal boundary over Europe as cold air ushers in from the NW into CNTRL and E Europe. Anomalous warm conditions continue along the Medierranean Sea and into SE Europe.

IFS-ENS clustering is tight with the vortex which approaches N-Germany. MSLP reading will be in the 990-995 hPa range with not much NWP shift in latest 6 runs (ICON/IFS and GFS). This LL vortex evolves along the exit region of a 3 sigma+ upper jet and works with impressive dynamics, whereas the NE European vortex decouples from the dynamic frontal zone with no further intensification forecast.

DISCUSSION

... Austria/SE Germany into Slovakia/N Hungary and Ukraine ...

Placed between both depressions, a W-E aligned frontal boundary is situated within the area of interest. Despite weakened background forcing as transient ridging builds in, IPV data hints at a weak embedded trough, which crosses that ridge and induces some background forcing during the daytime hours. Low-tropospheric response is forecast as a weak LL depression evolves somewhere along that boundary but ENS spread remains high for now where any LL vortex could spin up. This feature however should shift towards the Ukraine during the forecast with enhanced CAA/mid-level frontogenesis further upstream.
Hence expect no substantial net-motion of the boundary during the daytime hours before becoming CAA dominant thereafter.

Sliding W-E along this boundary indicates line segments with already dominant LL CAA regimes whereas other areas show a rather favorable WAA regime with near sfc based convection and strong directional shear. Also orography with blocked LL flow offers an enhanced CAPE plume e.g. just S of the mountainous areas. Futher S a drier BL keeps CI unlikely. A mix of elevated and more surface based activity is forecast in this broad level 1 area. A few long tracked supercells are forecast, which is impressive for this time of year.

DLS will be abundant for organized convection with a hail risk for storms, which ride north of the surface front in a weak/moderate MUCAPE regime. Any storm further S (e.g. along the immediate periphery of the surface boundary) could see a few near surface based supercells with an all kind severe risk, including a tornado or two and large hail with severe wind gusts.
Of concern will be the region over far S Slovakia/N Hungary, where inverted V profiles and environmental conditions supportive for long tracked supercells overlap, which could pose swaths of severe to damaging wind gusts and a local upgrade was performed.

SE Germany will also see near surface based activity with a few supercells forecast. Hail (isolated large), heavy rain and strong gusts become the main hazard but cannot rule out an isolated tornado event in a low LCL environment with strong SR inflow into deviating storms.

...Benelux into Germany ...

A very dynamic cold front passage is forecast during the daytime hours, which affects Benelux during the early afternoon and Germany thereafter.

Dynamics and kinematics are impressive with some weak prefrontal MUCAPE forecast especially from Benlux into W-CNTRL Germany. With forecast 0-3 km wind field, strong to severe wind gusts will be the main hazard with this frontal passage.

Regarding a QLCS tornado risk some signals arise from Belgium, Luxembourg into W-CNTRL Germany. There, 50 to 60 kt 0-3km shear vectors turn a bit more favorable regarding line orientation with strongest postfrontal pressure rise and placed just beneath the exit of an intense upper jet. However, prefrontal MUCAPE remains on the low-end side with drier prefrontal BL airmass and marginal moisture surge ahead of the front. An isolated embedded tornado event along forward racing surges is forecast - same for an isolated hail event with strongest storms.

Postfrontal convection flares up beneath cooling mid-levels with numerous thunderstorms forecast mainly from the Netherlands into far W/NW Germany. Uncapped and weakly unstable, those storms also have a chance to rotate with improving hodograph structures. Hail, strong to severe wind gusts and an isolated tornado are all possible. However, weakening diabatic heating works against this risk.

... The Czech Republic, E Germany into Poland ...

With WAA downstream of the incoming trough from the W, some low-tropospheric modification is forecast beneath cooling mid-levels (increasing lapse rates). Hence an extensive area with weak to moderate MUCAPE is forecast. Shear will be strong and supportive for a few multicell or an isolated elvated supercell event with large hail and heavy rain the main risk. Fast storm motion just to the S of the hodograph offers mostly crosswise vorticity to work with which should delay organization until some deviation occurs. So overall severe risk does not seem to justify a level 1 for now for many parts. A confined upgrade however was performed with ICON indicating a temporal time frame for surface based activity over far E Germany moving into W-Poland. Hail and gusts will be the main risk.