Storm Forecast
Valid: Fri 15 Aug 2014 06:00 to Sat 16 Aug 2014 06:00 UTC
Issued: Thu 14 Aug 2014 22:36
Forecaster: TASZAREK
A level 2 was issued for parts of Russia and Ukraine mainly for tornadoes, severe wind gusts, large hail and excessive precipitation
A level 1 was issued for N Italy, parts of Austria, Slovenia, Croatia, Bosnia and Herzegovina mainly for large hail and severe wind gusts
A level 1 was issued for area from parts of Balkan Peninsula to parts of Russia mainly for large hail, severe wind gusts and excessive precipitation
A level 1 was issued for south-eastern Spain and Balearic Islands mainly for large hail, severe wind gusts and excessive precipitation
A level 1 was issued for parts or North Sea and Baltic Sea mainly for waterspouts.
SYNOPSIS
Most of the European continent is covered by wide long-wave trough that is surrounded by jet stream extending from Spain, through Italy, Balkan Penninsula up to western Russia. Warm and moist tropial air masses are pushed into eastern and south-eastern Europe by extensive cold front on which severe convective phenomena are expected. Overlap of significant vertical speed and directional wind shear with moderate instability will provide perfect conditions for isolated supercells and linearly organized squall lines. Western, central and northern Europe will be covered by polar air masses where internal thunderstorms with low vertical wind shear environment are expected to occur. Mixing ratios around 7-8 g/kg and moderate lapse rates (6-7C/km) will provide rather weak (for this part of the year) instability (CAPE up to 500-600 J/kg). Except local hail up to 1-2cm, waterspouts, and rather weak convective wind gusts no severe weather threats are expected in this area.
Thunderstorms in the homogenius air masses should dissipate in the evening. Convection during night is predicted to be active along cold frontal zone in the eastern Europe and Baltic Sea that due to higher temperature than air above will provide instability.
DISCUSSION
...Northern Italy, Slovenia, parts of Austria, Croatia and parts of Bosnia and Herzegovina...
Mixing ratios around 10 g/kg in the southern foothills of the Alps will provide CAPE values up to 1000 J/kg. Significant flow in mid and upper levels resulting in DLS over 20 m/s may organise convective cells into multicellular and supercellular features. Although directional wind shear seems to be not high, local wind field environment associated with Alps may modify this and provide favorable conditions for mesocyclones. Within them large hail up to 3-4cm and severe wind gusts are expected in the late afternoon hours. Some portion of QG-forcing associated with advection of potential vorticity increases likelihood for thunderstorms in this area.
... Romania, Moldova, Ukraine, parts of Russia ...
Cold front pushing tropical warm and moist air masses into eastern Europe is covered almost on its whole area by strong thermal wind (jet stream). The overlap of frontal lift, instability up to 2000 J/kg, strong air flow in mid and upper levels and directional wind shear (0-3km SRH ~ 200-300 m2/s2) will provide good conditions for all kinds of severe weather threats. High 0-3km wind shear values will likely organize thunderstorms in linear features along cold frontal zone. Embedded bow echos and supercells may be capable of producing damaging wind gusts. The highest threat for large and very large hail will be located in the Romania and parts of Russia where overlap of highest instability, boundary-layer moisture and vertical wind shear is expected to be most favorable. Excessive precipitation threat will cover the part of frontal zone extending from Ukraine to Russia where rich vertical moisture profile (PW ~ 40-45mm) is predicted by NWP models. The area covered by lvl 2 denote region where conditions for tornadoes are the best. Locally CAPE up to 2500 J/kg will be accompanied by LLS ~ 10 and 0-1km SRH ~ 150-200 m2/s2. The highest threat for tornado will increase in 15Z and last until midnight. Thunderstorm activity along cold frontal zone should increase in the morning and will continue until late night.
... South-eastern Spain and Balearic Islands...
NWP models predicts that during late night weak instability will overlap with DLS ~ 20-25m/s and strong QG-forcing. Isolated supercells may be capable of producing severe wind gusts, large hail and excessive precipitation phenomena (PW over 40mm).
... Waterspouts ....
Cold air advection over Northern and Baltic Sea (that has water surface temperature higher than air above), together with weak wind shear may result in few waterspouts that may occur around 9-12 UTC in the coastal areas near convergent flows. Favorable ingredients corresponds also to moist low-levels, slow storm motion and good low-level instability. The highest threat is mainly related to areas where convective cells are likely: coastlines of Sweden, Denmark, Germany, Netherlands, and Baltic countries.
