Storm Forecast
Valid: Sun 28 Apr 2019 06:00 to Mon 29 Apr 2019 06:00 UTC
Issued: Sat 27 Apr 2019 19:53
Forecaster: TUSCHY
A level 1 was issued across S-Belarus and N-Ukraine mainly for excessive rain
A level 1 was issued for parts of NW Turkey mainly for large hail.
A level 1 was issued for far N Adriatic Sea mainly for excessive rain and a tornado threat.
SYNOPSIS
High-over-low block persist over N-CNTRL/CNTRL Europe. Closed off bubble of cold mid-level air stretches from Benelux to N-Italy to Romania. The main vortex is analyzed within the western part of that bubble with numerous smaller-scale cyclonic vortices rounding the base of the steering vortex. One vortex crosses Switzerland/N-Italy during the forecast from NW to E/SE with another one exiting W-Romania to the NW, dissolving over N-Hungary. Q-vector analysis indicates additional lobes with enhanced synoptic-scale forcing circling the main bubble from W to E.
Meager ridging is present over SW and SE Europe with latter ridging featuring too low thickness values for effective thunderstorm suppression. An outbreak of cold/continental air affects far NE Europe with leading southbound surging cold front offering some thunderstorm probabilities due to interaction with an unstable prefrontal air mass.
Beside the aforementioned cold front, a quasi-stationary wavy synoptic-scale boundary extends from the S Baltic Sea to the W Black Sea into the Aegean Sea. Crossed by the aforementioned synoptic-scale vortices persistent and scattered to widespread CI is anticipated over a broad area over E-Europe.
DISCUSSION
...E-/SE-Europe ...
Main foci for CI will be the synoptic-scale fronts and a broad/diffuse channel with lowered low-tropospheric pressure all crossed by weak mid-/upper waves/vortices. Isolated ongoing thunderstorms from the previous night and numerous showers limit diabatic heating, which could delay the main CI a bit. However, weak cap and various mesoscale/synoptic-scale lifting mechanisms assist in scattered to widespread CI during forenoon onwards. Main concern arises in the level 1 area, where 400-800 J/kg SBCAPE and very weak shear support clustering and slow moving convection with excessive rain the main hazard. Isolated large amounts of small hail are also possible with elongated/thin CAPE profiles and mixed near BL conditions including strong gusts with hydrometeor loaden/driven downdrafts. This activity persists during the night although a general weakening trend is forecast.
... Turkey ...
The flattening ridge and a crossing weak mid-level wave support daytime driven CI with peak severity and coverage during the afternoon/evening. Isolated thunderstorms persist well into the night, mainly over the mountainous areas.
Forecast soundings show 400-800 J/kg MLCAPE with weak shear but inverted-V profiles over CNTRL Turkey, where a few severe wind gusts are possible. Strongest cores contain marginal hail. Diffuse forcing precludes an upgrade.
Somewhat stronger DLS in the vicinity of the passing mid-level wave causes hodographs to enlarge a bit with some curvature in the 850-700 hPa layer while weakening rapidly aloft. Hence effective shear should be in the 10-15 m/s range and supportive of a few multicells with large hail and strong wind gusts (similar CAPE to areas further east). The hail risk caused an upgrade to a level 1. Most of the activity vanishes during the night despite a few non-severe elevated storms over far SE Bulgaria which move SE/offshore.
... N-CNTRL Mediterranean ...
Scattered thunderstorms erupt ahead of the approaching upper vortex from the NW as mid-levels cool atop residual low-/mid-tropospheric moisture over the N-Adriatic Sea and surroundings. Most of the activity should stay elevated with isolated large hail and strong to isolated severe wind gusts the main hazard. Don't want to exclude and isolated tornado event over the far N/NE Adriatic Sea, where LL cap weakens with an overlap of better curved LL hodograph structures. In addition a LL vortex evolves over the far NW Adriatic Sea, so modified BL wind field may assist in temporal training or at least banding of thunderstorms with an isolated excessive rainfall threat along the coasts and just inland. Cumulated threat caused an upgrade of that area.
... Benelux, Germany, E-France and Switzerland ...
Isolated non-severe thunderstorms are forecast with graupel and gusty winds. This activity decays beyond sunset.
