Valid: Sat 22 Jun 2013 06:00 to Sun 23 Jun 2013 06:00 UTC
Issued: Sat 22 Jun 2013 06:06
A level 2 was issued for the N Balkan region, Hungary, S Slovak Rep and W Romania for large hail, severe wind gusts and excessive precipitation.
A level 1 was issued for N-central Romania, W Ukraine, SE Poland and SW Belarus for large hail and severe wind gusts.
A level 1 was issued for N Algeria and N Tunisia mainly for large hail and severe wind gusts.
A low pressure system over N Ireland will continue eastwards towards the North Sea while occluding. Some mostly surface-based instability is found near the center of the low where wind shear is quite weak.
Remnants of an upper low are located over the central parts of Europe where a shortwave trough will move across Italy towards Poland during the day. This feature should lead to severe convective events in southeastern Europe due to a combination of moderate instability, strong shear and forcing.
Another upper low is present over Algeria and provides lift for convective initiation over N Algeria and N Tunisia where instability and strong shear are present.
...N Algeria / N Tunisia...
In an environment of low-end to moderate instability, strong vertical shear is present due to a branch of the subtropical jet stream. An approaching upper trough will lead to strong QG forcing which should easily overcome the -100 to -200 J/kg CIN barrier. The most probable scenario is isolated multicellular and supercellular convection with a high cloud base and therefore a threat of severe wind gusts. Large hail is also likely due to strong and persistent updraughts which may be created under these conditions.
An upper shortwave trough approaches a region of moderate instability with MLCAPEs in order of 1 - 2 kJ/kg. This feature should provide enough forcing to initiate convection. Due to steep vertical Theta-E gradients, the formation of intense cold pools is likely and a squall line may form from some multicells which have been initiated previously. This squall line will likely move along the region of maximum mid level wind speeds and likely not outrun the region of maximum forcing. Additionally, large hail will also be possible as any storm in this environment should have strong and persistent updraughts (organised multicells and also a few supercells are most likely in the southern part of the LVL2 area).
Apart from the large hail / severe wind risk, there is also a possibility of excessive precipitation if an organised MCS forms in a region where mid level winds are quite weak. Also, most multicells in the low wind - high instability region in the lower southern end of the LVL2 will tend to move very slowly and high PWAT should enhance the threat of excessive rain.
...Romania, SE Poland, W Ukraine and SW Belarus...
The convective systems which initially tend to form in the western / southwestern part of the LVL2 area will then move to the northeast. Further downstream, instability is not as ample as in the western parts and therefore a gradual weakening is expected. Some isolated multicells in the LVL1 region may also form prior to the arrival of a MCS and produce large hail and severe wind gusts.