Storm Forecast
Valid: Sun 19 Jun 2016 06:00 to Mon 20 Jun 2016 06:00 UTC
Issued: Sat 18 Jun 2016 23:17
Forecaster: PUCIK / GROENEMEIJER
A level 3 was issued for S Serbia, extreme NW Bulgaria and SW Romania mainly for large to very large hail, damaging wind gusts and to the lesser degree for tornadoes and excessive rainfall.
A level 2 was issued for E Bosnia, N Serbia, N Romania and S Ukraine mainly for large to very large hail and severe wind gusts.
A level 2 was issued for SE Hungary mainly for severe wind gusts, excessive precipitation and large hail.
A level 1 was issued for Central to S Italy mainly for large hail.
A level 1 was issued across Slovenia, SE Austria, Croatia mainly for large hail and excessive precipitation.
A level 1 was issued for Hungary, Slovakia, S Poland and NW Ukraine mainly for excessive precipitation, severe wind gusts and to the lesser degree for large hail.
A level 1 was issued for Central Ukraine and W Russia mainly for large hail, severe wind gusts and excessive precipitation.
SYNOPSIS
General pattern will persist over Europe with only a few changes. Thus, yet another very active period with severe thunderstorms is forecast across SE part of the continent. At 500 hPa, southern part of the deep trough will slowly begin its cut-off process. Enhanced flow, with speeds up to 30 m/s at 500 hPa level will rotate from the base of the trough over the Mediterranean towards the Balkans. Band of enhanced flow will be associated with a subtle short-wave trough, which will induce weak surface cyclogenesis over S Serbia and N Bulgaria. An easterly surface flow will advect moister airmass towards west, shifting the main area with severe weather risk in the same direction for this forecast period. Surface low is forecast to move northward with enhanced southerly 850 hPa flow on its eastern flank.
DISCUSSION
... S Serbia, NW Bulgaria, SW Romania ...
A very moist airmass characterized by dew points of around 20 deg C will yield moderate to high values of MLCAPE (1500 - 3000 J/kg), increasing towards south where steeper lapse rates (up to 8 K/km in 800 - 600 hPa layer) are simulated. At the same time, as mid-tropospheric flow strengthens with the approaching short-wave, DLS values will reach 20 - 30 m/s, yielding very conducive conditions for intense, well organised convection. Enhanced SRH values of 150 - 300 m2/s2 due to the surface easterly flow and veering vertical wind profile also point to the favourable conditions for supercells.
Storms may exist already early in the period especially west of the Lvl 3 area in response to the approach of the short-wave trough. Outflow boundaries, as well as convergence zones associated with the developing surface low will act as triggers for further development. Any supercell that initiates in this environment will likely produce large to very large hail and severe wind gusts. If supercells persist in isolated form into the evening hours, decreasing LCL and a slight increase in LLS will also enhance tornado risk. Even though low-level flow is not particularly strong, storm clusters may produce strong cold pools thanks to high CAPE values and organize into bow-echoes capable of swaths of severe to extremely severe wind gusts. Perhaps the highest chance of such development will be in the northern part of the Lvl 3. Heavy rainfall will also accompany the MCS, especially on its northwestern flank.
... N Albania towards E Bosnia ...
Lower moisture content and lower CAPE values point to the lesser risk of extremely severe weather than in case of Lvl 3 area. Nevertheless, strong vertical wind shear will still support well organised storms, including supercells capable of large to very large hail and severe wind gusts.
... N Serbia towards Hungary, Slovakia, S Poland, N Romania and Ukraine ...
During the day, isolated DMC may form along the Carpathian range over Slovakia, S Ukraine and Romania. It will likely become organised in moderate to strong DLS (15 - 25 m/s), including some supercells. Risk of very large hail will be present especially earlier in the forecast period over N Romania, N Serbia and extreme S Ukraine, where moister airmass and higher CAPE values are simulated. Towards the evening, storms will cluster into an MCS and progress N - NEwards in conjunction with the movement of the surface low. Numerous models depict this scenario and such MCS would be capable of severe wind gusts and excessive precipitation. Northwestern and northern extents of Lvl 1 are drawn where MCS may potentially be located Thursday 06 UTC.
... Central Ukraine to W Russia ...
Basically all models simulate a persistent MCS from the previous forecast period moving NE-wards. New convection will likely initiate along the outflow boundary / gust front of the MCS with threats of severe wind gusts, large hail and excessive precipitation in the environment of weak vertical wind shear (only around 10 m/s of DLS) but moderate CAPE (around 1000 J/kg).
... Central - S Italy ...
Even though models simulate only low CAPE values on the order of few hundreds J/kg, strong vertical wind shear may enable organisation of some of the cells into supercells, which may be capable of large hail.
