Large ridge is placed over western Europe while a slowly dissipating cut-off low is moving SW-wards towards northern Balkans. A strong mid-level jet streak wraps around this low. At surface, a cold front is extending from southern Poland over central Balkans towards N-ern Italy where still relatively high boundary layer moisture is in place. This area is the focus for today’s forecast.
Strong mid-level jet streak will bring very strong 0-6km bulk shear over out region, likely with 60-80kts which will help to rapidly organize any storm that could develop over northern Adriatic and NE-ern Italian plains, e.g. Veneto and Friuli regions.
As mentioned before, even there are mostly NE-ern with in the last two days on going over Slovenia and northern Adriatic, warm Adriatic sea waters managed to maintain near surface dewpoints which remained in low 10s. Additionally, with an approaching CAA with the cut-off low, a weak low pressure system is re-forming over north-central Italy which favour some backing winds in the low levels and warm and moist airmass from central Adriatic is advecting towards the northern Italy. Given the mostly NW-ern flow aloft, skies will remain clear through most of the day and relatively strong surface heating should take place.
Cut-off low with unusually low 500mb temps (-26 do -30°C according to all models) kicks in towards the evening and very steep mid-level lapse rates should overspread the region. A surface cold front, which became quasi-stationary over NW-ern Balkans in the last hours, will be forced SW-wards at the evening as additional forcing is expected once the trough ejects. Given the at least low 10s SFC dewpoints and very steep lapse rates, deep moisture convection seems possible and MLCAPE release of about 1000 J/kg can be expected.
Some storms are then expected to initiate alond the racing cold front or any near surface convergences that are clearly visible o the models, mostly in the coastal areas of Veneto region and over the Northern Adriatic sea between 16 and 21z tonight. Given the moderate instability and very strong 0-6km bulk shear, a few isolated severe storms are possible as any storms forming in this environment could organized into multicells or even a supercell or two. Very steep mid-level lapse rates pose a risk for very large hail possible around northern Adriatic (GFS simulates 4-6cm hailstones possible) as well some severe wind gusts given the higher values of DCAPE and high LCL. Limiting factor for storms to initiate behind the cold front with CAA could be a long living cloud cover along the front which couldn’t allow stronger heating to take place in the afternoon hours.
The next days don’t show anything severe weather possible, southern Alpine region will be under the diminishing cut-off low and mostly showers and moderate rainfalls seem likely. Temps will remain cool, once for awhile lower than average for May. Keep in mind that few days ago we were experiencing temps 5-8 degrees higher than average.