Storm Forecast
Valid: Wed 30 May 2018 07:00 to Thu 31 May 2018 06:00 UTC
Issued: Wed 30 May 2018 07:30
Forecaster: PUCIK
A level 2 was issued across E France, W Switzerland and NW Italy for excessive precipitation, large hail and severe wind gusts.
A level 1 was issued across N Spain, France, Italy, Germany, W Poland, W Czech Republic, Austria, Slovenia, Croatia and Bosnia mainly for excessive precipitation and large hail.
A level 1 was issued across Turkey mainly for excessive precipitation and large hail.
A level 1 was issued across Russia mainly for severe wind gusts and to the lesser degree for tornadoes.
SYNOPSIS
Over much of W, Central and S Europe, synoptic situation will remain very similar to the previous days. Scattered to widespread initiation of storms is expected across a large area in warm and moist airmass. Slow-moving and heavy rainfall efficient storms will once again pose a flash flood risk, while stronger updrafts will be capable of 2 - 4 cm hail. A broad Lvl 1 has been issued over this region and also Turkey for these setups. Initiation will be tied to local topography, convergence zones and outflow boundaries laid out by the overnight convection.
In the satellite imagery, several short-wave troughs are apparent in mid to upper troposphere, namely over Spain, the Northern Sea and over Poland. However, the most prominent vortex is rapidly moving SE-wards across Russia, along with a fast moving cold front. Here, synoptical situation is very different to the rest of Europe.
DISCUSSION
... E France / W Switzerland...
In a synoptic-scale lift ahead of the northward moving short-wave over Spain, widespread initiation is forecast over S France and Massif Central with storms quickly spreading northwards during the forecast period. Moderate buoyancy, with MLCAPE values around 1000 J/kg, is forecast. As mid-tropospheric flow will strengthen slightly, DLS values will reach 10 - 15 m/s, well organised multicells are expected. A few transient supercells are not ruled out particularly near the complex tropography enhancing the shear by modification of lower tropospheric flow. Large hail and excessive precipitation will be the primary threats, but severe wind gusts may occur as well as storms spread northward and cluster rapidly.
... NW Italy ...
Abundant lower tropospheric moisture is observed over the region with dewpoint readings between 16 and 20 deg C , yielding moderate to strong buoyancy during the day as daytime heating peaks. With northerly surface flow, pumped by the Appenines, DLS may locally reach up to 20 m/s. Thus, besides multicells, supercells may occur as well, particularly before the clustering begins. Large to very large hail will occur with this convective type. Otherwise, excessive precipitation will be the dominant threat.
... Russia ...
Marginal buoyancy, with MLCAPE values on the order of hundreds J/kg, will develop ahead of the fast moving short-wave and cold front. It seems likely that a strongly forced squall line will develop ahead of the cold front, surging SE-wards during the day. With 850 hPa winds reaching 20 - 25 m/s, severe wind gusts will be the primary threat. Given relatively low LCLs in the forecast soundings just near the cold front, as synoptic-scale lift moistens the environment, tornadoes are not ruled out either. However, their threat will be moderated by the lack of high SRH and also perhaps by convective mode favouring a squall line rather than isolated supercells.
... Algeria ...
Forecast hodographs reveal strongly curved and long hodographs with SRH values exceeding 300 m2/s2 just to the north of the surface low developing inland. Thus, anticipated convective type is long-lived supercells. Combined with steep lapse rates, a threat of very large hail and damaging wind gusts will exist. However, large discrepancies regarding the lower tropospheric moisture and the capping in the forecast soundings of individual NWP precludes an issuance of Lvl 2 at the moment.
