Storm Forecast
Valid: Sat 25 Nov 2017 06:00 to Sun 26 Nov 2017 06:00 UTC
Issued: Fri 24 Nov 2017 22:39
Forecaster: TASZAREK
No threat levels are issued.
SYNOPSIS and DISCUSSION
An eastwardly moving long-wave with an advection of arctic airmass covers NW and N Europe, and in the following hours will shift to CNTRL Europe. A blocking high is placed SW of British Isles while enhanced 1020 hPa pressure field covers S and E Europe. A shallow lows are located ahead of the approaching long-wave over N Poland and N Italy. A marginal lightning activity on Saturday is expected over 3 areas.
First one concerns North Sea and surroundings which are placed in the cold section of the trough. Over these areas a 200-400 J/kg MU CAPE will develop thanks to an impressive > 8 K/km lapse rates. Although multiple shallow convective cells will develop, a poor BL moisture will limit lightning activity only to occasional events.
Another area with a possible lightning activity covers E-CNTRL France and parts of S Germany where a shallow convection will develop thanks to the passage of the trough around afternoon hours. Under 4-5 g/kg MIXR and > 7.5 K/km lapse rates, a pockets of 100-300 J/kg ML CAPE will occur. The support of a good QG-lift and strong vertical wind shear may favour development of a shallow multicell clusters with small bowing segments, locally capable of producing severe wind gusts. Although according to NWP models CAPE will be low, instability may be enhanced by the steepening of the lapse rates within large-scale lift. Convection should fade in the late afternoon hours along with a sharp drop in instability.
A third area with a lightning activity covers E coast of Adriatic and W coast of Italy where pockets of enhanced BL moisture (7-8 g/kg) will be available to create 200-400 J/kg ML CAPE. Orographic lift associated with Werly flow and synoptic-scale upward motion associated with a low over N Italy will facilitate development of a rather shallow convective cells with a low severity potential. Convection should start around noon hours in the N section of the threat area and shift Sward for the rest of the forecast validity period.
