Valid: Thu 27 Jul 2017 06:00 to Fri 28 Jul 2017 06:00 UTC
Issued: Thu 27 Jul 2017 00:04
A level 2 was issued for north-western Turkey into north-eastern Greece, eastern Bulgaria and Romania, Moldova, and central Ukraine mainly for severe wind gusts, large hail, and excessive rain.
A level 1 was issued for north-western Russia mainly for severe wind gusts and tornadoes and to a lesser extent large hail.
The deep European trough accelerates east and starts to lift downstream of strong Atlantic jet streak than enters western Europe. This is associated with ridging across the western and central Mediterranean, whereas eastern Europe including the east Mediterranean is affected by the trough passage. Furthermore, a cut-off low moves east over north-western Russia. Maritime air masses spreading eastward behind the trough are characterized by weak lapse rates except for the main vort-max at the cyclonically sheared flank of the Atlantic jet streak that crosses Benelux and northern Germany. An elevated mixed layer is advected into the eastern Ukraine and southern Russia ahead of the trough. Steep lapse rates can also form close to the trough axis from Romania and Bulgaria towards Greece.
Eastern Aegean Sea and western Turkey into eastern Bulgaria, Romania, Moldova and central Ukraine
Ahead of the approaching trough, a frontal boundary is associated with convergence from the Aegean towards the Black Sea region. While a cold front moves east into western Turkey in the morning hours, the frontal boundary is quasi-stationary further north, with an elevated mixed layer spreading into the Black Sea region. CAPE in the order of 2000 J/kg is forecast. Along the complete boundary, thunderstorms are likely to form. Strong deep-layer vertical wind shear around 20 m/s will allow supercells to form, but MCSs with bowing lines are favoured given the strong forcing. Severe wind gusts are forecast from north-western Turkey towards the central Ukraine. Additionally, large and very large hail is forecast, especially when supercells form. An additional threat is excessive precipitation given large storm clusters moving northward along the frontal boundary. Tornadoes are not ruled out where storms interact with the sea breeze convergence over eastern Romania and southern Ukraine.
A strong mid-level jet streak moves east at the southern flank of the cut-off low. It affects an air mass characterized by initially weak lapse rates, but rich low-level moisture is present in the warm sector of the associated surface cyclone. Strong low-level vertical wind shear and favourably veering profiles are expected, and storms that form may become supercells, with the higher potential in the northern parts where deep layer vertical wind shear exceeds 20 m/s. These can produce large hail and tornadoes as well as severe wind gusts. Further south, deep layer vertical wind shear is weaker. Multicells are still capable of producing large hail and severe wind gusts, and also tornadoes are not ruled out.