Storm Forecast
Valid: Sat 25 Oct 2014 06:00 to Sun 26 Oct 2014 06:00 UTC
Issued: Fri 24 Oct 2014 21:05
Forecaster: SCHLENCZEK

A level 1 was issued for Scotland, the Norwegian coastline and the Norwegian Sea region mainly for severe convective wind gusts and to a lesser extent for tornadoes.

A level 1 was issued for the Bosporus region mainly for excessive precipitation and to a lesser extent for tornadoes.

SYNOPSIS

Quiet conditions are found over most portions of central and eastern Europe but there are still two regions in Europe where severe weather is likely to occur: An upper cut-off low over W Turkey tends to dissipate while remaining stationary. At its northeastern flank, excessive convective and non-convective precipitation is expected.

The other region of interest is the northern Atlantic where a developing cyclone will affect Scotland and the Norwegian coast. Some instability in a region of strong background flow and intense vertical shear may enhance some wind gusts which will likely exceed the 25 m/s threshold even without convection. The situation is particularly dangerous and the chosen threat level does only reflect the contribution of convection!


DISCUSSION

...Norwegian coastline / Scotland and isles...

An intense low pressure system W of Iceland is moving to the east while deepening to a minimum SFC pressure around 965 hPa. The core of this low is forecast to stay between Iceland and Norway on Sunday morning. Between the upper ridge over central and eastern Europe and this low, a huge pressure gradient leads to an intense large scale background flow. This low is preceded by an intense shortwave trough which should reach Scotland on Saturday morning and S Norway in the afternoon / evening. Close to the left exit of a 75 m/s jet streak at 300 hPa and some low-end instability is found due to advection of a tongue of moist air. Organized severe convection appears unlikely as the background wind shear is likely too strong to allow the formation of squall lines or low-topped supercells. Nevertheless, recent GFS and ECMWF runs suggest a threat of severe wind gusts in the entire area where locally gusts > 32 m/s are well possible. Convection may enhance the strength of the wind gusts but as no organized severe convection is expected, this scenario is covered by a LVL 1. Also, the STP and SCP values are enhanced in the highlighted area which may result in an isolated tornado. The severe wind threat will likely continue during Sunday.

...Bosporus region, W / SW Turkey...

A residue of warm and very moist air is found over the S Black Sea ahead of an upper cut-off low. Continuous advection of moisture towards the Bosporus region and QG lift from the trough in an unstable environment leads to long-lasting multicellular convection which will pose a threat of excessive precipitation. Locally > 10 m/s of LL shear and enhanced SRH1 and SRH3 may also allow an isolated tornado.