Valid: Fri 17 Jun 2016 14:00 to Fri 17 Jun 2016 20:00 UTC
Issued: Fri 17 Jun 2016 14:31
The tail of the cold front is moving from the E parts of Poland, Slovakia and Hungary into the west of the Ukraine and Romania in form of a distinct wind shift line. Ahead of it, mostly southerly low-level winds are present. Apart from areas where downslope winds have locally mixed out the low-level moisture, observed dewpoints are often around 20°C. The prefrontal air mass is hence probably characterized with CAPE around 2000 J/kg, 0-3 km vertical wind shear on the order of 20 m/s, veering low-level winds, and a strong capping inversion.
Latest satellite imagery shows enhanced cumulus clouds over the Ukrainian part of the Carpathians and in vicinity of the wind shift line in the bordering region of Serbia, Hungary and Romania. Isolated storms have recently formed over the W Ukraine and are expected to initiate near the wind shift line and/or over the hilly terrain of W Romania within the next few hours. They can quickly develop into supercells and pose a high risk of large or even extremely large hail (>5 cm).
Due to the strong capping inversion, the degree of storm coverage remains questionable. If the gust fronts of the first "cap breakers" can trigger secondary convection, upscale growth into an MCS is not ruled out over NW Romania and the adjacent Ukraine. In that case, severe downbursts, flash floods and an enormous amount of lightning become additional threats in the evening.
Due to plentiful sunshine, the temperature and dewpoint do only slowly decrease behind the wind shift line. The 12z Szeged sounding indicates that isolated storms may also still initiate behind the wind shift line in E Hungary. Their severe weather risk is still enhanced, albeit somewhat lower due to gradually decreasing instability and shear.