Storm Forecast
Valid: Sun 17 May 2015 06:00 to Mon 18 May 2015 06:00 UTC
Issued: Sat 16 May 2015 16:44
Forecaster: TASZAREK

A level 2 was issued for parts of Tyrrhenian Sea and S Italy mainly for large hail, severe wind gusts, tornadoes and excessive precipitation.

A level 2 was issued for Bulgaria mainly for large and very large hail and excessive precipitation.

A level 1 was issued for parts of Balkan Peninsula mainly for large hail.

A level 1 was issued for parts of NW Russia mainly for large hail.


SYNOPSIS

On Sunday weather in SW Europe will be driven by extensive Azores High that is set to inhibit convection in the most of the region. NW and N Europe will be covered by extensive geopotential wave with deep trough over Iceland and shallow one over Baltic Sea. This pattern is bound to provide flow of cold air of polar origin that in the belt from British Isles to Baltic Countries will remain marginally unstable. Another trough in NW Russia with well-developed unstable warm sector is about to produce thunderstorms in low sheared environment. Severe thunderstorm potential is forecast to occur in S and SE Europe on the border of polar and moist air of tropical origin. Most severe weather phenomena are due to occur within cut-off over Tyrrhenian Sea where high boundary layer's moisture content, steep lapse rates and high wind shear will overlap. Jet streaks during the forecast period are to occur in the belt from North Atlantic to Poland and over Sicilia.


DISCUSSION

...Tyrrhenian Sea and S Italy...

Cut-off that plunges into tropical air with moist boundary layer thanks to Mediterranean and steep vertical lapse rates is predicted to contain convective available potential energy up to 1500-2000 J/kg. Overlap of such instability with high moisture and strong low and mid level flow may result in any kind of severe weather phenomena. High DLS (up to 25 m/s) with 0-3km SRH (up to 300-400 m2/s2) that will occur especially in the morning hours is bound to create good condition for supercellular thunderstorms capable of producing large hail and severe wind gusts. Within the same thunderstorms, large LLS (~ 10 m/2) with 0-1 SRH (~ 150 m2/s2) and low LCL (600-800 m AGL) are set to provide conducive environmental conditions for tornadoes, especially if convective will remain isolated. Considerably high values of 0-3km shear (> 20 m/s) and good QG lift on the eastern and north-eastern side of the trough may organize convection into linear feature creating potential for the severe wind gusts. MCS in the late afternoon and evening hours cannot be ruled out, especially if the persistent QG lift and CAPE exceeding 1000 J/kg is due to occur. The highest threat for severe weather is expected to fall on eastern Sicilia and Calabria in the afternoon hours. Thunderstorms are expected to go on during the whole forecast period, especially in the eastern and north-eastern part of the trough. Since the area of convection will remain in one region, some local excessive precipitation with threat for flash flooding cannot be ruled out.

...Balkan Peninsula...

On the border of polar and tropical air thunderstorms are expected to occur on the unstable side of the tropical air with cool mid-level flow aloft. Such pattern will provide over Bulgaria great overlap of high boundary layer's moisture (up to 10-11 g/kg) with steep lapse rates (> 7 C/km). Although wind shear is not forecast to be high (DLS ~ 15 m/s), the CAPE up to 1500-200 J/kg and favorable vertical moisture profile may result in large to very large hail. Convection should start when the diurnal heating will be the highest (1200-1500 UTC). Later on thunderstorm may cluster and organize into multicellular feature. Given very high PW values over Bulgaria (> 30mm) and relatively low storm motion, excessive precipitation and local flash flooding cannot be ruled out. Less severe thunderstorms are also forecast to occur along the Dinaric Alps where orographic lifting will support convection. The main threat within these thunderstorms is large hail up to 2-3cm. Thunderstorms within Balkan Peninsula should weaken in the evening hours.

...NW Russia...

Well-developed warm sector that encircles trough from its northern and western side provide good overlap of relatively moist boundary layer (mixing ratio up to 8-9 g/kg) and steep lapse rates (> 7 C/km). CAPE in such environment is likely to reach up to 1000-1500 J/kg. Since mid and low level flow is expected to be marginal (DLS ~ 10 m/s), no severe weather phenomena associated with convection is likely to occur except large hail up to 2-3cm that is possible in the region with the most favorable moisture profile (denoted by level 1 area). Thunderstorm should start with the peak of the diurnal heating and weaken in the evening hours.