Storm Forecast

Storm Forecast
Valid: Thu 19 Oct 2023 08:00 to Fri 20 Oct 2023 06:00 UTC
Issued: Thu 19 Oct 2023 08:38

A level 2 was issued across S Portugal and extreme SW Spain mainly for damaging wind gusts, tornadoes and heavy rainfall.

A level 1 was issueda cross Portugal and SW Spain mainly for severe wind gusts and tornadoes.

A level 1 was issued across the Balearic Sea mainly for severe wind gusts.

A level 1 was issued across SE France mainly for heavy rainfall and tornadoes.

A level 1 was issued across NW Italy mainly for heavy rainfall and to the lesser degree for tornadoes and large hail.

A level 1 was issued across the E Adriatic coastline mainly for heavy rainfall, large hail and to the lesser degree for tornadoes.


... W Iberia ...

A pronounced short-wave trough and a cold front is forecast to cross the area during the day. Ahead and along the front, abundant low-level moisture is forecast. However, the mid-tropospheric lapse rates will remain mostly below 6K/km, yielding at best skinny CAPE profiles. A low CAPE, high shear situation is forecast over the area. Especially over the SW part, very strong lower tropospheric flow is forecast, with 1 km windspeeds exceeding 30 m/. Long and curved hodographs are simulated with 0-1 km bulk shear exceeding 20 m/s and 0-500 SRH 200 m2/s2. Surface-based storms forming in this environment will be capable of damaging wind gusts and tornadoes. Given the strong forcing, it is possible a quasi linear convective system with embedded bowing segments will form. Heavy convective rainfall is forecast as well, given low LCLs, deep warm cloud layer and strong horizontal moisture transport towards the area ahead of the front. That said, the zone of the storm initiation will quickly translate across the area and the very heavy rainfall shouldn't be of a very high duration.

... Balearic Sea ...

As the cold front arrives over the coastal regions and the Sea, an increase in thunderstorm activity is forecast along it. Given strong lower tropospheric flow, an evolving band of storms may be capable of isolated severe wind gusts. Tornado threat will be rather low as 0-1 km bulk shear should stay mostly below 10 m/s.

... SE France ...

Two rounds of storms are forecast across the area, in the morning hours and then in the late evening and overnight hours, coincident with the arrival of the short-wave trough from Iberia. During both times, heavy rainfall will be the main threat. Heavy rainfall will be more pronounced in the latter period as the low-level jet will increase with 850 hPa windspeeds locally exceeding 25 m/s. A tornado threat will be present in the morning hours over the northern edge of the area and in the overnight hours over the coastlines. While at both times, models simulate strong low-level shear, main question is whether surface-based storms can develop.

... NW Italy and E Adriatic coastline ...

Scatterred storms are forecast to initiate throught the orographic lift along the coastlines. Strong low-level shear is forecast across both domains. Strongly curved hodographs with high values of SRH are simulated especially over the E Adriatic. However, much of the low-level hodograph will not effective for storms as these will tend to remain elevated. This will greatly reduce the tornado risk. Heavy rainfall will be the primary risk over both areas, followed by tornadoes given that a surface-based storm can form and large hail. Large hail will be most likely over the E Adriatic, where the shear over the 1 km is simulated, as well as the highest CAPE values in the cold part of the cloud.

... Central France to England ...

A marginal threat of tornadoes will exist over the area given modest low-level shear. However, rather poor low-level lapse rates and uncertainty concerning the corridor of the strongest shear currently precloude the issuance of the level.

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