Storm Forecast
Valid: Sat 18 Jun 2016 06:00 to Sun 19 Jun 2016 06:00 UTC
Issued: Sat 18 Jun 2016 06:09
Forecaster: TASZAREK/PISTOTNIK

A level 3 was issued for NE Romania, N Moldova and parts of Ukraine mainly for very large hail, damaging wind gusts and excessive precipitation.

A level 2 was issued for parts of N Balkan Peninsula, Moldova, CNTRL Ukraine and parts of W Russia mainly for large hail, severe wind gusts and excessive precipitation.

A level 1 was issued for parts of W Russia, SE Finland, W Ukraine, Moldova, SE Poland, Slovakia and N Balkan Peninsula mainly for the large hail, severe wind gusts and excessive precipitation.

A level 1 was issued for Alpine region mainly for excessive precipitation.

A level 1 was issued for NE Spain, N Algeria and N Tunisia mainly for large hail.

SYNOPSIS

Low associated with severe weather outbreak from Friday continues to move northward and pushes a cold front spreading from Baltic Countries up to NW Balkan Peninsula further east. In front of it, an impressive influx of a tropical highly unstable airmass in the warm section reaches the White Sea. Subtropical jet streak extends from W Mediterranean trough Italy, W Ukraine up to NW Russia. In the area of steady geopotential field in N Balkan Peninsula and CNTRL Ukraine, an overlap of high to moderate thermodynamic instability with the eastern edge of the jet takes place. Within this area, severe thunderstorms are expected. CNTRL and W Europe remains in the cold sector with weakly sheared environment and low to moderate instability. Thunderstorms are also possible over W Mediterranean where within an overlap of low instability and jet streak may locally become severe.

DISCUSSION

... N Balkan Peninsula, Moldova, CNTRL Ukraine, W Russia...

This area stretches in the tropical airmass where a low-level moisture convergence takes place in the axis from CNTRL Romania up to W Russia. Thanks to this, low-level moisture jumps to an impressive 14-16 g/kg (mixing ratio) and given steep lapse rates (> 7 K/km) and strong diurnal heating, develops CAPE up to 2500-3000 J/kg (mostly 1000-2000 J/kg). The jet stretches parallel to the convergence axis and interferes with instability zones on its eastern edge. Thanks to this, a moderate to high DLS of 15-25 m/s is overlapping in the areas where CI is expected. Thunderstorms are most likely to develop early around 09-12 UTC thanks to lifting factors such as warm air advection, a slight PVA lobe, orographic lift and ongoing outflow boundaries from remaining nighttime thunderstorms. It is expected that thunderstorms over Romania and Moldova may quickly organize into supercells with a potential of producing damaging wind gusts (given high CAPE and moderate shear) and very large hail (given steep lapse rates), and then cluster into northeastwardly moving MCS. Because of the parallel flow relative to the convergence zone axis, a training convection will pose a high threat of excessive precipitation and local flash flooding, especially given extremely moist vertical moisture profile (PW ~ 40-45mm). Northern edge of the level 2 will remain under a lower shear, but the increased threat of severe thunderstorms will result from heavy rain and large hail in a very high CAPE environment. An approaching MCS in the evening hours may also produce additional severe weather. Southern edge of the level 2 will remain under better overlap of CAPE (2000-2500 J/kg) and DLS (20-25 m/s), but with the strongly capped environment and less pronounced large-scale lift. If any thunderstorm will develop in this conditions, it may quickly evolve into supercell and pose a threat of severe to extremely severe weather. The main threat is related to large and very large hail, the secondary involves heavy rain and severe wind gusts. Models are not consistent with CI and convection clustering, but because of the possibility of a few supercells in the late afternoon hours, a level 2 is justified. Tornado threat in the whole level 2 area is strongly limited by the lack of increased values of LLS and unfavourable wind profile in low-levels. However, given high CAPE and moderate DLS an isolated event cannot be ruled out.

...Alpine region...

Behind the cold front, most of the areas are covered with few hundredths J/kg of CAPE and a weakly sheared environment. Although vertical moisture profile (PW ~ 20-25 mm) limits excessive precipitation threat, an almost stationary persistent convection superimposing with a large-scale precipitation in the Alpine region, creates a threat of local flash flooding.

...NE Spain, N Algeria, N Tunisia...

A local overlap of low instability within moisture convergence zones and a subtropical jet streak with DLS up to 20-25 m/s, poses a threat of local isolated severe thunderstorm. Given lapse rates exceeding 7 K/km and a low-level mixing ratios of around 9-10 g/kg in NE Spain, a large hail up to 2-3cm is possible. Over N Algeria and N Tunisia, a stronger lapse rates (> 8 K/km) and instability (CAPE > 800 J/kg) may result in a large hail up to 3-4cm.

...SE Poland, Slovakia, W Ukraine...

Behind the cold front, a developing CAPE up to 400-600 J/kg overlaps with the western edge of the jet streak and increases DLS up to 20-25 m/s. PVA in the afternoon hours supports CI and as a result, a large hail up to 2-3cm and isolated severe wind gusts within supercell/multicells are possible.

...W Russia...

In the warm sector with the tropical airmass and weakly sheared environment, a CAPE will develop up to 1500-2000 J/kg. Thunderstorms developing along the cold frontal zone and ahead of it may be capable of producing large hail up to 2-3cm and severe wind gusts within organised bowing segments of the linear convective features.