Storm Forecast
Valid: Mon 23 Feb 2015 06:00 to Tue 24 Feb 2015 06:00 UTC
Issued: Mon 23 Feb 2015 03:05
Forecaster: VAN DER VELDE

A level 1 was issued for the British Isles for chances of severe convective wind gusts and tornadoes.

A level 2 was issued for western Ireland and western Scotland mainly for severe convective wind gusts.

A level 1 was issued for Crete, southwestern Turkey and the Aegean Sea mainly for large hail.

SYNOPSIS

A deep low pressure system (<948 hPa in GFS model) moves to the north of Scotland. Its tight pressure gradients over the British Isles combined with the convective activity developing in the cool airmass pose a risk of severe wind gusts. The main cold front belonging to the low advances into Spain, France, Germany and southern Scandinavia, and into the western Mediterranean at night, triggering a new round of thunderstorms.
Another low has been active in the central Mediterranean for the last two days and will split into two, one over Greece and the other invigorating over the Ligurian Sea as colder air advects into the western Mediterranean, contrasting with the present relatively warm airmass resulting from the southerly flow in the central Mediterranean basin.

DISCUSSION

...Ireland and Scotland...

The threat is particularly concentrated along the west coast as most of the energy for thunderstorms in the unstable airmass is supplied by the lapse rate between ocean and cold mid levels. WInds over 30 m/s at low to mid levels can be transported to ground as severe wind gusts in convective downdrafts. Over land, the friction causes strong low-level wind shear >17 m/s which can support tornadoes, if strong updrafts could be maintained. Convection will initally (09-12Z) be organized linearly along the occlusion curled up around the low and will likely pose a more concentrated threat. A second round with more clustered storms should occur in the evening at the passage of a shortwave trough.

...Crete and SW Turkey...

Unstable warm airmass, low-level convergence and strong vertical shear created by the jet stream should combine into a healthy setup for storm systems advecting to Crete and southwestern Turkey from the south. Locally, large precipitation sums may occur and in the strongest cells large hail is possible. The chance of tornadoes is somewhat elevated though low-level shear and 0-3 km SREH are not large in most areas.