Storm Forecast
Valid: Sun 28 Nov 2010 06:00 to Mon 29 Nov 2010 06:00 UTC
Issued: Sun 28 Nov 2010 08:24
Forecaster: SCHLENCZEK

This forecast is issued 2 hours later due to software problems. We apologize for this inconvenience.

A level 1 was issued for the western and southwestern parts of Italy mainly for excessive rainfall and severe wind gusts and to a lesser extent for large hail and tornadoes.

A level 1 was issued for the coastal regions of the S Adriatic and N Ionian Sea mainly for excessive rainfall and large hail and to a lesser extent for tornadoes and severe wind gusts.

A level 1 was issued for W Turkey and the Bosporus region mainly for large hail and to a lesser extent for severe wind gusts and tornadoes.

SYNOPSIS

A large low pressure system is present over western and central Europe. At the southern tip of the upper trough, cyclogenesis is expected over the N Mediterranean. The southern branch of a 45 m/s upper jet streak points towards Greece where unstable air is advected northwards. Severe weather is most likely along the coastal regions of the S Adriatic and Ionian Sea and later in the period also in the Aegean towards the SW Black Sea.

DISCUSSION

...Atlantic, Bay of Biscay...

In the vicinity of the upper cold core, a few hundred J/kg CAPE are present in a weakly sheared environment. With a mixing ratio around 3 g/kg, this airmass is rather dry but almost dry adiabatic lapse rates are forecast from the warm sea surface up to 4 km AGL. Therefore, an isolated waterspout is not ruled out.

Some isolated thunder is also possible over the North Sea but low-end CAPE and moisture suggest that lightning will be too sparse for a low probability thunderstorm area.

...Tyrrhenian Sea, W / SW Italy...

Ahead of the developing surface low, some 400 - 600 J/kg MLCAPE are in place with deep layer shear in order of 15 - 20 m/s. Most of the shear is confined to lower levels which should reduce the probability of organized severe thunderstorms. Given quite strong LLS and enhanced (200 - 400 mÛ/sÛ) SRH1, there is a possibility of isolated tornadoes. The 20 - 25 m/s southwesterly winds at lower levels (850 to 700 hPa) may also lead to isolated severe wind gusts. Although effective PWAT is not that high, local excessive rainfall and flooding are possible due to numerous storms which will make landfall. In the late night hours, overall thunderstorm coverage and intensity will tend to decrease.

...S Adriatic, Ionian Sea, S Balkans...

Some 1000 - 1500 J/kg MLCAPE are present ahead of the left exit region of a 40 m/s upper jet streak. Sufficient QG forcing is expected and well-organized storms may form in an environment with 25 - 30 m/s deep layer shear (15 - 20 m/s in the 0-3 km layer) and locally 10 m/s LL shear. Associated with the unstable region, a narrow band of enhanced 200 - 400 mÛ/sÛ SRH1 stretches from Crete towards the N-central Adriatic. Current thinking is that some multicells and supercells may produce all sorts of severe weather with a pronounced large hail and excessive rainfall threat. Thunderstorm development will likely start on Sunday morning / afternoon and will continue at least until Monday morning. Despite very good conditions for severe thunderstorms are given at first, only a level 1 is issued to cover this threat as storms will either stay too isolated or storms will merge into a rather messy MCS structure. The evolution of a bowing line segment is not completely ruled out but it appears less likely than the other possibilities which are mentioned above.

...Bosporus region, Aegean Sea, W Turkey...

Ample MLCAPE is also present over the eastern parts of the Aegean and the Turkish coast but strong capping should preclude initiation until the late evening (CIN around -200 J/kg). If some isolated multicells or supercells manage to form, those storms will likely produce large hail, isolated severe wind gusts and maybe an isolated tornado. The tornado threat is much less pronounced than the other types of severe weather as the LL lapse rates are not very favourable for tornadogenesis.