Storm Forecast
Valid: Sun 25 Mar 2018 06:00 to Mon 26 Mar 2018 06:00 UTC
Issued: Sat 24 Mar 2018 21:01
Forecaster: TUSCHY

A level 2 was issued across parts of the Ionian Sea, the Aegean Sea and Greece for large to very large hail, excessive rain, severe wind gusts and a few tornadoes. A strong tornado event can't be ruled out.

A level 1 was issued for S-Italy and parts of Albania mainly for excessive rain.

A level 1 was issued for NE-Algeria mainly for excessive rain.

A level 1 was issued for NW-Algeria and NE-Morocco mainly for excessive rain.

A level 1 was issued for far N-Spain mainly for excessive rain.

SYNOPSIS

A blocked pattern with a firm anticyclone being placed over CNTRL Europe continues during the forecast. Numerous low amplitude waves circle the high pressure area to its south and impact the Mediterranean.


DISCUSSION

...Malta to the Aegean Sea ...

The most impactful and organized thunderstorms occur in the highlighted area during the forecast.

Before noon, a thinning warm sector due to the ongoing occlusion process features ample CAPE/shear. Forecast soundings in that area indicate a strongly and deeply veered flow regime with increasing mid-level winds as a 30 m/s 700 hPa speed max ejects out of the vortex' base to the NE. Lapse rates beneath 850 hPa remain weak with rather stable conditions but they steepen aloft, offering enlarged mid-level CAPE profiles. Hence the main threat over the Ionian Sea seems to be a large hail risk. Betimes, as convection approaches the W-coast of Greece, LL lapse rates increase a bit with mixing of the LL air mass (dissolved warm sector), which could also increase the risk of more surface based activity with severe wind gusts and an isolated tornado event. However with broad mid-level CAPE profiles (400-800 MUCAPE) and DLS of up to 30 m/s, the risk of large hail seems to stay the main hazard and even a very large hail event over S-Greece can't be ruled out.

During the night, the severe risk shifts further NE and affects the Aegean Sea and surrounding areas. A similar setup is anticipated. Forecast hodographs show curved signatures up to 700 hPa just ahead of the incoming synoptic-scale front, but again, rather stable LL should limit the risk of gusts/tornadoes. Nevertheless, careful examination of the data indicates a confined spatiotemporal overlap with better LL stratifications during the frontal passage and hence the risk of a tornado or two and severe wind gusts won't be zero. In fact anticipated SRH of more than 300 m^2/s^2 in the lowest 1 and 3 km also point to the possibility of an isolated strong tornado event. In combination with a continued risk of large to very large hail (hail size in excess of 5 cm), the complete area was upgraded to a level 2.

Another risk is excessive rain especially along the W-/NW-coast of Greece and Albania with the vortex placed over the Tyrrhenian Sea, advecting a moist and unstable marine air mass onshore during the night. Most models keep the QPF amounts in a robust level 1.

Slow moving thunderstorms beneath the vortex (over S-Italy and the Tyrrhenian Sea) bring heavy to locally excessive rainfall amounts next to an augmented waterspout risk due to steepened LL lapse rates.

The other level 1 areas see a prolonged period of onshore flow with repeatedly onshore moving showers and thunderstorms. Flash flooding in those areas will be a distinct possibility!