Storm Forecast
Valid: Sat 07 Nov 2015 06:00 to Sun 08 Nov 2015 06:00 UTC
Issued: Sat 07 Nov 2015 03:37
Forecaster: DAFIS
A level 1 was issued for parts of Ireland, England, Netherlands, N Germany, Denmark and Poland mainly for severe wind gusts and tornadoes.
SYNOPSIS
The positive titled ridge over SW Europe will move further north during Saturday, whilst a shortwave trough is formed in its NW edge, moving fast eastwards from the UK towards Poland until Sunday morning. Near the surface, a low pressure system will form, following the axis of the trough and it will remain over the North Sea until the end of this forecast. A strong high pressure system over the rest of the continent, will suppress any convective activity. On the contrary, Tunisia and areas around Cyprus will experience some short living thunderstorms, most of them remaining off shore and without posing any threats.
DISCUSSION
.... Level 1 areas ....
NWP models predict the formation of the shortwave trough over Ireland, early in the morning of Saturday. At the surface, the low pressure system will be visible on the maps a few hours later and the large-scale lift may suffice to create marginal CAPE with equilibrium levels high enough to allow deep convection with weak lightning activity. The UK will experience some heavy downpours but mostly by stratiform rain with some embedded storm cells with low to moderate lightning activity. GFS produces MLCAPE of about 400 J/kg over the UK and Denmark, under very high sheared environment, with a jet streak crossing all the level 1 area. CAPE will overlap with 0-6km bulk shear of even more than 30 m/s and the SREH0-3km parameter will be in the range of 300 - 400 mē/sē, so any storm that forms will be able to become severe producing severe wind gusts of more than 25 m/s. We have to mention that non-convecting gusts will certainly be more than the convective reports as gale wind force winds are forecast especially near the shores. The greatest threat for tornadogenesis exists over the central UK and Denmark, where low level shear will reach and may exceed the 15 m/s, overlapping with CAPE. Moreover, low LCL values and 0-3km wind shear of 15 - 20 m/s are sufficient ingredients to pose a tornado threat. Excessive rainfall may not be the main issue as the cold front moves quickly eastwards and PW does not exceed the 3 cm. The low CAPE values and some disagreements between the models prevent us from issuing a level 2.
