Storm Forecast
Valid: Sat 25 Nov 2023 06:00 to Sun 26 Nov 2023 06:00 UTC
Issued: Fri 24 Nov 2023 23:06
Forecaster: KUZMENKO/PUCIK
A level 2 was issued across W and NW Turkey mainly for severe wind gusts and tornadoes, followed by heavy rainfall and marginally large hail.
A level 2 was issued across SW/S Turkey and Cyprus mainly for large to very large hail and tornadoes, followed by heavy rainfall and severe wind gusts.
A level 1 was issued across W Greece mainly for heavy rainfall.
A level 1 was issued across SE Ukraine/SW Russia mainly for heavy rainfall and to a lesser degree severe wind gusts.
DISCUSSION
... E Aegean Sea, NW Greece, Turkey ...
A two round severe weather situation is forecast across the area, linked to the passage of two troughs. The first trough is forecast to move from the S Aegean Sea across S Turkey and further E between the morning and afternoon hours. The second, deeper, trough is forecast to approach the area in the late afternoon to evening hours. As the trough overspreads the frontal zone, rapid cyclogenesis is forecast across the Black Sea overnight. As the surface low moves quickly to the NE, a surface cold front will cross the Aegean Sea and much of Turkey by Sunday 06 UTC.
The first round of storms, over S Turkey, will also benefit from a plume of steep lapse rates advected from Africa, yielding high values of buoyancy in the hail growth zone. Combined with 0-6 km shear locally exceeding 30 m/s, there will be a high probability of large hail in supercells. Very large hail can't be excluded either. Besides large hail, tornadoes will also be possible along the coastlines, where the low-level shear should be stronger with 0-1 km bulk shear exceeding 10 m/s and high values of SRH due to the curved hodographs. CAPE is forecast to increase towards the S, where also drier mid-troposphere is simulated, raising questions about the likelihood of convective initiation over Cyprus. However, models do simulate convective precipitation in an environment of CAPE > 1000 J/kg and an impressive wind profile conducive to intense supercells. Thus, decided to include the island in the Lvl 2.
The second rounds of storms will also form in an environment conducive to supercells. Ahead of the front, models unanimously simulate a strong low-level flow with wind speed reaching up to 25 m/s at 850 hPa and 0-1 km shear exceeding 20 m/s, indicating a threat of severe wind gusts. In case linear segments develop, the formation of bow echoes is also possible. In addition, the low cloud base and high values of streamwise vorticity (SHR values in the lowest 500 m exceeding 300 m2/s2) point towards a high likelihood of tornadoes, especially in the W and NW part of Turkey, where the hodographs are most curved. Moist thermodynamic profiles and skinny CAPE, with most of it located in the warm part of the cloud, signify that heavy rainfall can be expected along the west and south coastline of Turkey and Greece. Continuous strong onshore flow is likely to cause redevelopment of storms, leading to local flash floods. The thunderstorm activity will be ceased only after the cold front passage.
... S Ukraine / extreme SW Russia ...
A warm, quasi-stationary front will reside over the area throughout the day, with MUCAPE > 500 J/kg in a strongly sheared environment. The primary threat will be heavy rainfall and possible flash floods, due to the continuous redevelopment of storms along the front, as well as severe wind gusts due to the intense 0-3 km bulk shear up to 30 m/s. This threat will be limited by the expected elevated nature of the storms. Should the storms become surface-based, tornadoes will also be possible.
