Storm Forecast
Valid: Tue 11 Oct 2016 06:00 to Wed 12 Oct 2016 06:00 UTC
Issued: Mon 10 Oct 2016 20:23
Forecaster: DAFIS

A level 2 was issued for S Greece mainly for excessive rainfall, large hail, severe wind gusts and to a lesser extent isolated tornadoes.

A level 1 surrounds level 2 area for the same threats with less coverage. Waterspouts are expected near the coasts.

SYNOPSIS

An unseasonably high pressure system is located over Scandinavia and a mid-level vortex affects Central Europe. Several short-wave troughs surround both systems with the most interesting one found over the SE Europe during Tuesday. An overlap of the cyclonically curved mid/upper jet and modest CAPE create a set up favorable for well organized DMC around Greece. At the surface, a well organized low pressure system approaches the Iberian Peninsula from the Atlantic, but most of the accumulated precipitation over Portugal and Spain is expected to be non-convective. Plenty of stratiform rainfall is also expected in eastern parts of the continent, especially in Romania. Low level clouds and fog prevail in NE parts.

DISCUSSION

... Greece and W Turkey ...

As south-easterly winds advect an high-ThetaE air masses towards the coasts of Greece, forecast soundings show deep moisture with PW atop 30 mm and curved hodographs within the increasing mid-level jet. SSTs up to 25°C (represented by the latest satellite-AVHRR data) and temporarily steepening mid-level lapse rates are adequate for some widespread ~ 2 kJ/kg MLCAPE build-up over Mediterranean Sea. At the early morning hours, west coasts of Greece will experience intense thunderstorms as strong DLS (>20 m/s) and high MLCAPE (1.5 kJ/kg) overlap, increasing the threat of a supercell formation. Some clusters may be able to propagate E-SE but due to weak thermodynamic instability, they will not pose a threat over the continental parts of the country. A level 1 area was highlighted for the westward facing coastal areas, mainly for excessive precipitation (assisted by training convection and orographic lifting), severe wind gusts and marginal large hail (more to the south).

WAA with influx of very moist Mediterranean air masses will also affect the SE continental parts of Greece and the Aegean Sea, but a rather high uncertainty exists among the several high resolution models regarding convective initiation (CI). Low level humidity and CIN vary among the models, as well as where the dominant convergence zone will be formed but if storms succeed to form inside this strongly sheared environment will pose a severe threat. Not only the overlap of DLS/CAPE is enhanced, but also the SREH0-3km values exceed 200 m²/s² creating an environment conductive for supercells, producing all kinds of severe threats. The areas having the greatest chances for this scenario are highlighted by a level 2 area, where heavy rainfall (locally excessive amounts possible - amounts up to 100 mm/24h) and isolated large hail will be the main threats. Apart from the aforementioned risks, LL directional shear increases along the coast/onshore areas, so we cannot rule out a few rotating updrafts with an isolated tornado event. Waterspouts are expected near the coasts of Greece and Turkey, depending on the local sea/land breeze patterns. In the afternoon of Tuesday, storms will shift to Turkey's coasts where orographic lifting will play a crucial role to the intensification of thunderstorms with a flash flood threat highlighted by a level 1 area. Further south drier/capped air mass precludes significant thunderstorm development.