Storm Forecast
Valid: Tue 09 Nov 2010 06:00 to Wed 10 Nov 2010 06:00 UTC
Issued: Tue 09 Nov 2010 00:09
Forecaster: KOROSEC
A level 2 was issued for western Mediterranean sea mainly for strong wind gusts, tornadoes and excessive convective rainfall.
A level 2 was issued for western Balkan coastal regions and eastern coast of Thyrrenian sea mainly for intense and persisting excessive convective rainfall, strong to severe wind gusts, large hail and tornadoes.
A level 1 was issued for surrounding the level 2 area over much of central Mediterranean, parts of Greece and eastern Aegean sea mainly for strong winds, tornadoes and excessive rainfall.
A level 1 was issued for coastal areas of Bay of Biscay mainly for excessive rainfall, marginally large hail, a couple of tornadoes and strong winds.
SYNOPSIS
Another complex convective scenario over much of Europe with impressive large and deep trough centered over west-central Europe. While the main deep surface low is weakening, moving from the southern UK into France, a serie of secondary surface lows are rapidly moving along the southern flank of this trough across northern and central Mediterranean sea. Those will bring another day of mainly excessive rainfall as well as severe storms more to the south across the west-central Mediterranean sea.
DISCUSSION
... western Balkan coastal regions and eastern coast of Thyrrenian sea ...
Areas within the level 2 will be in the highest threat for persisting and locally very intense rainfalls, where strong southerly flow will be advecting warm and moist airmass northwards into north-central Mediterranean. A rather impressive jet streak with several embedded disturbances will be more than supportive for persisting upslope flow from the Tyrrhenian and south-central Adriatic sea onshore. Combined with embedded deep convection, given the marginal instabillity and strong deep-layer shear in place. Expect organized severe storms capable of producing strong wind gusts, locally intense rainfall as well as a couple of tornadoes (or waterspouts) along the coasts as rather impressive SR helicity and especially LL wind shear (above 20 m/s) values will be present. High amounts of accumulated rainfall across the level 2 areas (several models are quite confidently simulating 100-200mm/24hrs especially over extreme western Balkans) could bring flash floods and landslides, especially where training-effect of the storm cells/clusters will occur.
A threat level 1 was extended well around the whole Italy and Adriatic sea, as well as across Greece and the eastern Aegean sea where at least some threat for severe storms or excessive rainfall exists, but will be less robust than across the highlighted areas above.
... western Mediterranean sea ...
During the early afternoon hours when strong PV anomaly digs into western Mediterranean, steepening lapse rates and large scale ascent ahead of it support widespread deep convection along/ahead the strong surface cold front extending towards the central Italy. With very impressive shear/SREH values in place, an organized severe storms will form. Widespread convective activity seems likely, possibly merging into larger clusters in late afternoon/early evening hours, moving ENE-wards across the level 2 area towards Sardinia and Corsica. Locally excessive rain, a few tornadoes/waterspouts and strong winds can be expected while any large cluster could signifficantly enhance flash floods threat if the persist over some areas for longer time.
... Bay of Biscay with coastal areas of northern Spain and western France ...
With very cold mid-levels in the wake of the large deep trough, widespread (rather shallow) convective activity is expected around the Bay of Biscay. Though the strong NW flow limits the higher shear, it will support persisting upslope flow across the highlighted areas within the level 1. Large rainfall amounts will be the main threat. However, it seems that stronger cells will also bring marginal hail, strong winds and tornado/waterspout threat, as high LL CAPE and 800-1000m AGL LCLs will be in place.
