Storm Forecast

Storm Forecast
Valid: Thu 01 Aug 2013 06:00 to Fri 02 Aug 2013 06:00 UTC
Issued: Wed 31 Jul 2013 22:55
Forecaster: GATZEN

A level 1 was issued for Ireland mainly for tornadoes and severe wind gusts.

A level 1 was issued for Scotland and parts of northern England and Wales mainly for large hail.


An intense and amplifying Atlantic trough moves slowly eastward into Europe. The central European ridge amplifies due to downstream development and intense warm air advection. At the end of the period, it will extend well into Scandinavia, where the actual trough will cut off and move into the Baltic States. This situation will be associated with cold air advection from Scandinavia into eastern Europe.

Most of Europe is dominated by anticyclonic flow and synoptic-scale convergence zones are not expected. The boundary-layer is relatively dry and lapse rates are quite weak. Across western Europe, increasing low-level moisture and the advection of steep lapse rates from the south-west will result in instability during the period.


Ireland and surroundings

Warm air advection will affect the British Isles for most of the period. A plume of moist air masses originating from the subtropical Atlantic will spread north-east and continues northward until Friday. This air mass indicates weak lapse rates as indicated by latest soundings.

Main focus of convective activity will be the low-level jet ahead of the cold front that enters Ireland in the evening hours. The strong moisture transport within this low-level jet will be accompanied by strong QG lift due to a short-wave trough embedded in the strong mid-level jet that exceeds 25 m/s in the afternoon hours. Therefore, the maritime air will likely become unstable with moist adiabatic lapse rates in mid-levels and slightly steeper lapse rate in the boundary-layer in response to diurnal heating.

Current thinking is that showers and thunderstorms will develop in the warm air advection regime. These storms will have a good potential to organize in an environment with 10 m/s 0-3 km vertical wind shear and also around 10 m/s bulk shear in the lowest kilometre. The rather broad overlap of low-level vertical wind shear and CAPE supports a threat of supercells capable of producing tornadoes. These storms may also produce large hail. Furthermore, bowing storms may form with the main threat being severe wind gusts. Highest potential is expected across western Ireland. Late in the period, the cold front moves eastward. A few severe wind reports may still be possible until the morning hours.

British Isles, North Sea, Denmark, northern Germany

At the northern flank o the warm air advection regime, a tongue of rich low-level moisture will extend from the British Isles to northern Germany and slowly moves northward. At mid-levels, steep lapse rates have started to spread northward and will overlap with the moisture. Current thinking is that elevated storms will develop over a broad region. During the day, storms will have a greater potential to root to the boundary-layer. Storms that form may be capable of producing large hail and tornadoes given the moderate low-level vertical wind shear. Main potential will be the British Isles, but a weak threat cannot be excluded for northern Germany and Denmark. Limiting factor will be the increasing capping inversion that will suppress deep moist convection further to the south.

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