Storm Forecast

Storm Forecast
Valid: Sat 30 Jan 2016 06:00 to Sun 31 Jan 2016 06:00 UTC
Issued: Sat 30 Jan 2016 00:18
Forecaster: TASZAREK

A level 1 was issued for part of British Isles mainly for the severe wind gusts.


A 1025-1030hPa high pressure complex covering S parts of Europe inhibits convective activity on the most of this area. Exception is the weakly pronounced cold drop E of Gibraltar where a fading DMC is forecast in the early forecast hours. A main polar jet stream stretches from Atlantic through S part of British Isles, North Sea, Baltic Sea up to W Russia. Within a forecast period, a long wave will pass from British Isles to Poland. A cold front with a marginal thermodynamic instability but rich precipitation fields will travel through most of the Central Europe. A main threat for thunderstorms lies in the cold sector behind the front where according to NWP models a passage of a secondary shortwave is expected. CAPE thanks to impressive lapse rates (> 7.5 C/km) will jump over marine areas to few hundredths J/kg, but will not overlap with any "good" vertical wind shear (although the low and mid-level airflow will be strong  700hPa 20-25 m/s). The thunderstorms will be mostly low-topped with poor boundary layer's moisture content (mixing ratios ~ 2-3 g/kg), but low elevation of a lightning-favorable graupel zone allows to increase lightning probability to a 50% threshold. A better overlap of a high shear underneath the jet streak (but with marginal thermodynamic instability) will take place over CNTRL and N part of British Isles where NWP models predicts convection. This area will experience in the afternoon hours >25 m/s severe wind gusts thanks to the passage of the shortwave with a strong horizontal pressure gradient and winds up to 30 m/s at 850 hPa. A convective enhancement of the gusts is likely in Scotland (where the CAPE is most promising) but it is also not ruled out in the CNTRL part of British Isles and Ireland. However, due to a poor boundary layer's moisture content, marginal CAPE over land surface and a lack of significant lifting mechanism only a level 1 is issued.

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