Severe storms expected across Algeria, Morocco, SW Mediterranean and S Spain
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Valid: Thu 12 Sep 2019 06:00 to Fri 13 Sep 2019 06:00 UTC
Issued: Wed 11 Sep 2019 22:31
Forecaster: GATZEN- A level 2 was issued across northern Algeria mainly for large hail, tornadoes, severe wind gusts and to a lesser extent extreme rainfall.
- A level 2 was issued across the south-western Mediterranean and south-eastern Spain mainly for extreme rainfall and to a lesser extent large hail, severe wind gusts, and tornadoes.
- A level 1 was issued across northern Algeria, north-eastern Morocco, south-western Mediterranean and south-eastern Spain for large hail, tornadoes, severe wind gusts and extreme rainfall.
Discussion
Synopsis
Former tropical storms move across northern Europe, associated with rising geopotential over central Europe. Two cut-off lows affect southern Europe, one centered across the Morocco – Algeria border, and one digging across the Balkans into the Aegean. Both vortices are associated with steep lapse rates that partly overlap with rich Mediterranean moisture.
Discussion
Algeria and Morocco into the south-west Mediterranean and southern Spain
Conditions become increasingly favourable for organized convection across northern Algeria and Morocco during the period. Moist low-level air masses are advected south-westward into the Atlas mountains. Atop of the boundary layer, south-easterly winds advect an elevated mixed layer into the area. High MLCAPE up to locally more than 3000 J/kg can build across Algeria. Initiation of storms is forecast in the evening along a frontal boundary extending from north to south that will slowly move westwards as a warm front.
With 20+ m/s deep layer vertical wind shear and curved, long hodographs (0-3 km SRH 200+ m²/s²), supercells are forecast, capable of producing large to giant hail, severe wind gusts, and local flash floods. Tornadoes that may be strong are also forecast due to strong low-level vertical wind shear and rather low LCLs. Storm motion vectors almost parallel to the frontal boundary supports clustering of convection later in the period, and an MCS may form, with an increasing wind and flood threat during the night.
From the south-west Mediterranean to southern Spain, lapse rates and low-level buoyancy are weaker. However, plentiful moisture and a low-level easterly flow with storm motion vectors nearly parallel to a convergence zone can result in echo training during the period. Skinny CAPE profiles are forecast and the main threat is excessive precipitation and flash floods. Additionally, large hail, severe wind gusts and tornadoes are forecast given strong vertical wind shear.
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