Storm Forecast
Valid: Thu 10 Nov 2011 06:00 to Fri 11 Nov 2011 06:00 UTC
Issued: Wed 09 Nov 2011 18:55
Forecaster: GATZEN
A level 1 was issued for east Sicily mainly for excessive precipitation.
SYNOPSIS
A high over the Baltic Sea will be quasi-stationary during the period. Low geopotential expands between two troughs from the Bay of Biscay across the central Mediterranean to the Black Sea. A new vort-max will move from the Bay of Biscay south-eastwards and will reach northern Italy at the end of the period. The rather cold mid-level air mass will be associated with steep lapse rates from the Bay of Biscay to southern Italy and the south Aegean. As rich low-level moisture will remain over the same region, instability is likely over a broad area. Lift is expected near the trough centers of the Biscayan trough and the Mediterranean trough centred over southern Italy, where thunderstorms will likely develop. Additionally, scattered storms may develop along convergence lines over the west Mediterranean Sea.
Strong vertical wind shear is not expected over most regions with thunderstorm potential that limits the potential of storm organization. The best potential is expected to the north of the Pyrenees where increasing westerly mid-level winds will overspread easterly low-level winds, resulting in 15 m/s DLS and slightly favourably veering profiles in the afternoon hours. However, the threat of large hail seems to be too low to issue a level 1 forecast.
So the main threat will be excessive rain due to slow-moving storms over the Mediterranean. This threat has decreased since the last period and is forecast to be too low for a level 1 over most of the area as well. The highest potential was highlighted by the level 1 over eastern Sicily, where best lift and low-level moisture are in place and storms may affect the same region throughout the period.
Late in the period, a cold front will enter western Iberia ahead o the Atlantic trough. Strong low-level vertical wind shear is forecast to the east of this cold front and will overlap with rich low-level moisture. However, lapse rates are forecast to be rather stable. Lift ahead of the approaching trough may lead to increasingly deep mixed air and weak instability may allow for shallow convection. These storms may be capable of producing tornadoes given rather large low-level hodographs / SRH up to 400 mē/sē in the lowest kilometre. However, given the weak lapse rates that are expected, a level 1 is not issued at this time. Later data may allow for more confidence about the development of instability, and an update may be warranted.
