Storm Forecast
Valid: Fri 23 Oct 2009 06:00 to Sat 24 Oct 2009 06:00 UTC
Issued: Thu 22 Oct 2009 20:00
Forecaster: TUSCHY

A level 2 was issued for the coastal areas of the E/SE Adriatic Sea and the Ionian Sea, SE-Italy and parts of Greece mainly for excessive rainfall and severe wind gusts.

A level 1 surrounds the level 2 mainly for severe wind gusts and locally heavy rainfall.

SYNOPSIS

A strong low pressure affects the central Mediterranean with unsettled conditions. This depression moves slowly southeastwards, crossing the Tyrrhenian Sea. Another strong depression draws near to Ireland during the night hours with wind gust approaching our severe criterion. Otherwise, quiet conditions convective-wise persist, either warm and stable over the Iberian Peninsula or cold over N/NE-Europe.

DISCUSSION

... Parts of Italy and the coastal regions of the Adriatic Sea and the Ionian Sea...

An unusually strong depression - central pressure down to 994hPa - crosses the Tyrrhenian Sea from the NW. At the same time, attendant cold front, initially placed over Italy and the west Ionian Sea, advances eastwards during the forecast and affects most parts of the Adriatic and Ionian Sea.

During the early morning hours, the cold front is about to exit extreme SE Italy, where conditions for severe thunderstorms are still conducive. Numerous thunderstorm clusters from the overnight convection persist or re-develop while moving offshore. Diffluent upper streamline pattern and a strong LLJ assist in widespread, deep convection, so heavy rainfall will most likely be the dominant risk in the level 2 area. Models differ somewhat in the final speed of this boundary, but it looks like the most serious flash flood risk persists during the daytime hours and gradually decreases from north to south as the moist influx weakens/shifts southwards. Shear in GFS, especially over the N-Ionian Sea looks impressive but is most likely contaminated due to the convective feedback problem. In addition, the main storm mode ought to be clusters of storms. Nevertheless, directional shear along the coast ramps up significantly, which also points to a tornado risk, especially if more discrete storms evolve or beneath the "tail-end charlie" along MCS features. Parts of Greece were included into the level 2 but the overall risk for more widespread excessive rain decreases over central/eastern Greece due to a weakening LLJ and diminishing CAPE. However, the rest of Greece may be upgraded later-on, if conditions for excessive rainfall look more favorable.

Along the backside of the depression, new convection is forecast. LL shear over Sicily would be adequate high for severe wind gusts and hence a level 1 was issued. However, most of the thunderstorm activity ought to be confined to the coldest mid-levels, where shear decreases rapidly.

... Ireland 03 UTC onwards ...

A strong depression approaches Ireland during the night hours from the WSW. A strongly sheared warm sector covers Ireland and some MUCAPE is forecast. Even without electrified convection, severe wind gusts are possible within showers. Only the southern/western parts of Ireland were highlighted, bound to the position of the cold front.