Storm Forecast
Valid: Sat 29 Jul 2017 06:00 to Sun 30 Jul 2017 06:00 UTC
Issued: Sat 29 Jul 2017 01:27
Forecaster: TASZAREK
A level 2 was issued for parts of W Russia mainly for large to very large hail, severe wind gusts, excessive precipitation and tornadoes.
A level 1 was issued for W Russia, E Belarus and N Ukraine mainly for large hail, severe wind gusts and excessive precipitation.
A level 1 was issued for N Italy and Alps mainly for large hail, excessive precipitation and severe wind gusts.
A level 1 was issued for N France, Benelux and NW Germany mainly for severe wind gusts.
A level 1 was issued for NE Spain and SW France mainly for large hail, severe wind gusts and excessive precipitation.
SYNOPSIS
Widespread thunderstorm activity with a potential of producing all kinds of severe weather is expected over E Europe. The highest threat for surface-based supercells capable of producing very large hail and tornadoes concerns late afternoon hours and area marked by level 2 over W Russia. Storms with a large hail, heavy rain and severe wind potential will be possible over Alpine area in the afternoon hours. Late and uncertain convective development with a possible supercell and multicell clusters is plausible over NE Spain/SW France. Low-topped storms with severe wind potential and under strong synoptic-scale lift are expected to develop in the late evening over N France and move to Benelux during nighttime.
DISCUSSION
...NW Europe...
Almost stationary large low covers British Isles. On its southern flank a jet streak stretches from Atlantic, through N France, S British Isles, Benelux and up to N Germany. A passage of the shortwave trough with high kinematics and marginal instability is expected by NWP models over N France and Benelux in the evening and nighttime hours. In the environment of high wind shear, small instability and decent QG-lift, a low-topped convection capable of producing severe wind gusts is predicted to develop in the late afternoon hours over N France and move NEwardly to Benelux and NW Germany in the evening and nighttime hours. Given very dynamic wind field and linear forcing, a development of a squall line with bowing segments and damaging wind gusts cannot be ruled out.
...NE Spain / SW France...
Under the influence of a shortwave, also storms over NE Spain and SW France should "fire-up" quite late, around 18 UTC. Given LL SE inflow of a moist air from Mediterranean and EML with 7 K/km lapse rates, ML CAPE over Spain may develop up to 1500-2000 J/kg but with evident cap. NWP models are not consistent in simulating CI, but if storms will overcome CIN and develop, an overlap of 15-20 m/s DLS may support evolution of multicells clusters and supercells capable of producing large hail, severe wind gusts and heavy rain.
...Alpine area...
A weak shortwave passes Alpine area in the afternoon hours. As a result a slowly moving cells are expected to develop in the environment featuring weak shear and small to moderate instability. Storms may be capable of producing locally marginally large hail and excessive rain. Downburst/microburst type severe wind gusts are also involved within these storms. Thanks to mountains interacting with a wind field, a 2-3 supercells with a large hail and severe wind potential cannot be ruled out.
...Eastern Europe...
Over Eastern Europe, a weakening broad low with a well-developed moist and highly unstable warm sector is moving Nwardly. This synoptic feature caused a widespread storm activity with an MCS on Friday evening and nighttime hours through Saturday. Within the support of a consistent broad moisture advection from Black Sea, it is expected that storm clusters will continue on Saturday morning, through afternoon and evening hours. Within the support of a strong diurnal heating, EML from Asia and well developed convergence zone, a new surface based storms are expected to "fire-up" in the afternoon hours and in the environment of > 2000 J/kg ML CAPE, mostly on the N and NE flank of the low. Roughly 15 m/s DLS and curved hodographs with SRH03 exceeding 200-300 (locally > 400) m2/s2 may organise convection into supercells with a potential of producing large to very large hail and tornadoes, especially over N flank of the low (around triple-point) where SRH01 and low-level jet along with LLS (> 10 m/s) are the highest. Multicell clusters will also pose a threat of excessive precipitation (PW > 40) and severe wind gusts. Low is predicted to occlude and cut-off its warm sector in the late afternoon hours. One or two large MCSs should form in the evening and move Nwardly. Severe thunderstorm activity should continue on Sunday in the similar area when diurnal heating and further moisture advection will regenerate environment.
