Valid: Sun 24 Aug 2014 06:00 to Mon 25 Aug 2014 06:00 UTC
Issued: Sun 24 Aug 2014 06:39
Forecaster: VAN DER VELDE
Levels 1 and 2 were issued for eastern Romania/Bulgaria and southern Moldova mainly for large hail and severe wind gusts.
A level 1 was issued for northern Ukraine mainly for a chance of tornadoes.
A level 1 was issued for northeastern Spain mainly for isolated large hail and severe wind gusts.
A level 1 was issued for parts of Sweden and surrounding areas for spout-type tornadoes.
A level 1 was issued for northern Algeria and Tunesia mainly for large hail and severe wind gusts.
A broad upper trough shifts into Ukraine and Belarus. Surface low pressure centers lie over western Ukraine and Moldova as well as the southern Norway/Sweden border. The former is dynamically active with a deep PV intrusion moving over a zone of warm humid air pulled in from the Black Sea before the cold front. The latter is a barotropic low filled with unstable air. Western Europe is kept calm by an extension of the Azores High.
...Bulgaria, Romania, Ukraine...
At the time of writing (06Z) a fast-moving MCS is already active over southeastern Romania. Severe wind gusts can occur at the linearly organized segments. However radar seems to suggest the system is diminishing. The continued presence of CAPE around 1000 J/kg in GFS suggests a later revival of storms may occur, but probably mostly outside the path of the old MCS. The shear environment is moderate (15-20 m/s DLS), allowing multicells and some supercells. Medium LCL heights support the large hail threat. Severe gusts are supported by Delta-theta-e of 15-20 degrees. Deeper into Ukraine, near the occlusion, very strong 0-1 km shear and low LCLs suggests a threat of tornadoes, where currently lightning is observed, but this area should have low CAPE from elevated parcels only.
GFS indicates a modest CAPE without much capping, in some 15 m/s deep layer shear. An isolated large hail (and perhaps severe gust) event from a multi/supercell storm is possible.
...Baltic Sea, Denmark, Sweden, Norway, Finland...
Highlighted with level 1 is the area where convective cell motion and low level wind speeds will be really slow, with good low level buoyancy and convergence zones providing vertical vorticity to be stretched into updrafts, manifesting as funnels which locally may be F0-F1 tornadoes. These tend to form easier over water but are possible over land.
Very high based convection may be possible with a chance of severe wind gusts/dust storms and large hail. Some storms may become supercells given the 15 m/s DLS.