Valid: Tue 27 Oct 2020 06:00 to Wed 28 Oct 2020 06:00 UTC
Issued: Mon 26 Oct 2020 21:04
A level 1 was issued for Croatia, Italy, Malta, and Greece for excessive precipitation, severe convective wind gusts, and large hail.
A long-wave trough with a neutral tilt is found in western Europe, with an axis extending from the North Sea towards the western Mediterranean. Downstream of this trough, synoptic ascent is expected and a strong southwesterly low-level flow of unstable air masses in South Italy and the western Balkans will result in DMC events. In addition, surface cyclogenesis is expected in the Ionian Sea during the early morning on Wed 28/10, when an anticyclonic Rossby wave break over Central Europe will create a cut-off low over the Mediterranean. This development will result in severe weather events in Greece, but mostly after the end of this outlook.
.... Croatia, Italy, Malta and Greece ....
A lee-cyclogenesis in North Italy has created an elongated cold front crossing the whole country, all the way south to the northern coasts of Africa on Mon 26/10. Ahead of this front that is moving east, unstable air masses will bring warm and moist air onshore, over Italy and the western Balkans on Tue 27/10. Developing storms will locally produce high amounts of precipitation in short periods of time, and in Italy and Malta, most of the available NWP models show an overlap of more than 1000 J/kg MLCAPE and more than 15 m/s DLS. This environment will be favorable for all kinds of severe weather events, especially near the coasts. Large hail and severe convective wind gusts are possible. A few waterspouts in the Ionian and Adriatic Seas cannot be ruled out.
During the early morning on Wed 28/10, a surface cyclone will develop in the Ionian Sea. The strong vertical tilt of this cyclone suggests a potential for intensification due to strong baroclinicity. The developing warm front will bring heavy rain in the western and southern parts of Greece by 06z on Wed 28/10. CAPE will be significant mostly over the sea, but the strong DLS shows the potential of organized DMC which can affect the coasts of Greece. Also here, all kinds of severe weather are possible, excessive rainfall, large hail and severe wind gusts, but there is a high uncertainty whether storms will reach the coasts of Greece by the end of this outlook, so a level-2 cannot be justified with the current data. Finally, a favorable environment for tornadogenesis is forecast in the southern parts of Greece due to high values of LLS and SREH0-1km, where MUCAPE exceeds 1000 J/kg.