Storm Forecast

Storm Forecast
Valid: Tue 22 Nov 2011 06:00 to Wed 23 Nov 2011 06:00 UTC
Issued: Mon 21 Nov 2011 20:50
Forecaster: KOROSEC

A level 1 was issued for eastern Spain mainly for excessive rainfall.

A level 1 was issued for southern Italy mainly for excessive convective rainfall, marginal hail, strong/severe winds and a brief tornado or two.

A level 1 was issued for eastern parts of Sardinia and Corsica mainly for excessive convective rainfall.


A broad upper ridge persists across much of Europe while two separate upper low affect W-CNTRL Mediterranean. One upper low translates from NW Iberia towards Marocco coast by Wednesday morning, while another low sits just north of African coast. This low slowly moves towards southern Italy. Connected to this low, a well defined SFC cyclone gradually weakens during the forecast period.


... eastern Spain ...

Yet another day of enhance rainfall threat for coastal areas of eastern Spain. Although the low makes gradual progress towards east and wind field weakens over the level 1 area, persisting LL flow from the sea seem still to support healthy orographic precipitation. Models also have marginal instability just offshore there, which could support a few storms as well and additionally rise the precipitation sums there. A marginal threat level has been issued for this reason. However, within very poor wind shear, no seriously organized deep convection can be expected.

... eastern parts of Sardinia and Corsica ...

Models are in good agreement of excessive convective rainfall threat over this area with rather strong persisting flow from the ESE on the front side of the moving upper low/SFC cyclone/frontal zone. Some instability combined with marginal deep layer shear should support some intense storms, moving rather slowly inland and produce intense rain. A cluster of storms cannot be ruled out either, staying over the same areas for longer period of time. Locally, storms could produce some stronger wind gusts as well. Easterly LL flow will produce intense orographic precipitation immediately onshore.

... southern Italy ...

On the front side of the low, warm advection overspreads the southern Italy and results in unstable airmass. Quite strong southerly LL jet is expected ahead of an approaching SFC frontal zone from the WSW. This should first support orographic precipitation while around 20 m/s of shear combined with moderate instability should produce severe storms. Those will be capable of producing locally some hail, intense rainfalls and winds. Nicely veering wind profiles with height will enhance SR helicity and therefore support rotating storms as well. A couple of supercells as possible as well, rising the threat for a tornado or two where LL shear/SREH will be maximized.

Especially SW Mediterranean sea highlighted with high lightning probability lines is prone to produce some waterspouts given the rather warm SSTs and quite cold mid levels beneath the upper cold core and low geopotential heights.

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