Storm Forecast
Valid: Sun 11 May 2014 10:00 to Mon 12 May 2014 06:00 UTC
Issued: Sun 11 May 2014 10:38
Forecaster: PUCIK
A level 1 was issued for France for marginally large hail.
A level 2 was issued for Northern Italy for large to very large hail, damaging wind gusts and to the lesser degree for tornadoes and excessive precipitation.
A level 1 was issued for parts of Slovenia, Austria, Croatia and Hungary for large hail, severe wind gusts and to the lesser degree for tornadoes and excessive precipitation.
A level 1 was issued for Poland and the southern Baltics region mainly for marginally large hail and severe wind gusts.
SYNOPSIS
An active weather pattern is forecast for Europe with strong zonal flow across much of Western and Central Europe. A short-wave trough is now situated over Central France as of 10 UTC, quickly progressing eastwards. A frontal boundary is running from N Spain towards N Italy, SE Austria, Slovakia and Poland. Lee cyclogenesis to the south of Alps resulted in the development of weak surface low over NW Italy. Especially close to the frontal boundary, isolated to scattered DMC is forecast with the greatest potential in a belt from N Italy towards Hungary.
DISCUSSION
... France ...
A low end Lvl 1 is issued for some scattered post frontal convection that will form in moderate vertical wind shear and marginal to low CAPE. Nevertheless, cool mid-level temperatures along with rather steep lapse rates between 800 and 600 hPa might aid in some marginally large hail occurrence with stronger multicells. Other threats should be minimal.
... Northern Italy ...
A potentially dangerous setup is evolving over this region. Surface observations reveal dewpoints around 14 °C with backing low-level flow due to the falling surface pressure. With short-wave trough approaching region, steep mid-level lapse rates will overlay rather moist boundary layer, resulting in low to moderate CAPE values. Intense vertical wind shear is forecast, with DLS values 30 to 45 m/s. Although hodographs should be mostly straight, easterly to southeasterly surface winds ahead of the surface low will result in enhanced SREH with around 150 m2/s2 in the 0-3 km layer. As such, conditions will be prime for supercells with threats of large to very large hail and damaging wind gusts. Tornadoes might occur as well as well due to very strong vertical wind shear although cloud bases could be quite high in the early afternoon - therefore tornado threat will be most prominent towards the evening.
Degree of initiation is in question today, but pronounced short-wave and associated lift will likely erode CIN by late afternoon. As storms shift eastwards towards the evening, strengthening low-level jet might feed upscale growth of convection with evening / overnight MCS over Venezia region. Subsequently, threat of excessive precipitation will become the dominant one.
... SE Austria, N Croatia, Hungary ...
Ahead of the frontal boundary, moist boundary layer along with steepening lapse rates due to the lift ahead of the advancing trough will result in marginal to moderate CAPE values. 500 hPa flow around 20 m/s will result in moderate to strong DLS with values ranging from 15 to 25 m/s. Setup will likely be conducive for well organised multi / supercells capable of large hail and severe wind gusts. Towards the evening, strengthening LLS could result in a few tornadoes in case that isolated supercells manage to persist. Clustering of convection towards late evening into an MCS along the advancing front might result in some excessive precipitation occurrence.
... Eastern Poland towards the Baltics ...
Strong DLS values are simulated over the region with marginal to low CAPE values in cool, moist airmass behind the frontal boundary. Scattered, low-topped DMC will initiate thanks also to PVA ahead of the trough. Stronger multicells and possibly also supercells might be capable of marginally large hail and severe wind gusts.
