Storm Forecast
Valid: Mon 16 Oct 2017 06:00 to Tue 17 Oct 2017 06:00 UTC
Issued: Mon 16 Oct 2017 00:40
Forecaster: VAN DER VELDE

A level 1 was issued for W Ireland and W Scotland mainly for isolated tornadoes.

Note: Extremely severe winds are forecast for Ireland, produced by synoptic/mesoscale conditions which are outside the scope of our convective threat level system.

SYNOPSIS

A large part of Europe is under anticyclonic conditions with stable weather. On Sunday, the southwestern flow over the Atlantic has carried a hurricane intensifying to category 3 into European waters. This system is currently transitioning rapidly into a strong post-tropical cyclone as it moves to Ireland. Cold air mass has now wrapped around the core, forming a cold front and occlusion leading into an isolated warm core. This cold front should touch the south coast of Ireland by 06Z. The core of the low is forecast by GFS run of 18Z to track along the west coast of Ireland, with a dramatic pressure gradient of about 25 hPa across Ireland at 12Z. Models forecast the strongest winds along Ireland's south coast around 12Z of up to 40 m/s sustained with 10m gusts in the 160-180 km/h range. This should cause widespread damage, but since deep convection no longer plays a role in it, we do not issue level 3 for this. The other component is excessive rain, and models predict 30-50 mm rain mainly along the Irish west coast, with a possible convective contribution.

DISCUSSION

As we are concerned with convective severe weather threats, the occlusion north of the low is the most interesting. Although is predicted to contain only 100-300 J/kg MUCAPE, often from elevated parcels, very strong winds veering with height create 300-600 m2/s2 of 0-3 km SREH and over 17 m/s 0-1 km shear vectors. This supports tornadogenesis if convection really manages to form and stay alive. Differential theta-e advection in the low levels could destabilize the situation. The highest potential for development is along the west coast of Ireland. After this band, only shallow convection seems possible. Isolated thunder may occur elsewhere (SW UK, W France) from elevated convection.