Storm Forecast
Valid: Sun 20 Dec 2015 06:00 to Mon 21 Dec 2015 06:00 UTC
Issued: Sat 19 Dec 2015 21:53
Forecaster: TASZAREK

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

A level 1 was issued for SW Norway mainly for the excessive precipitation.

SYNOPSIS and DISCUSSION

An extensive high covers most of the Balkan Peninsula. A filling-up cold drop is centered over Sicilia, and within this system a convection is likely. However, due to a relatively warm cloud tops a lightning prediction covers only a 15% probability. During a forecast period, a long geopotential wave with a weakly pronounced cold front will pass through a British Isles, North Sea and parts of Benelux. Within this system boundary layer's moisture content up to 4-6 g/kg (near-surface mixing ratio) will overlap with a broad area of steepening lapse rates (up to 7 C/km) and result in a CAPE up to 200-400 J/kg (mostly over water surface). A dynamic wind field with advection of PVU and MLS up to 20 m/s that will cover the instability field may organize a low-topped convection into an isolated thin bowing lines capable of producing severe wind gusts. However, due to a marginal instability over the land areas, the threat is rather low, on the border of level threats of 0 and 1.

A strong orographic lift is expected by the NWP models on the south-western coast of the Norway. A presence of thermodynamic instability and favorable advection of PVU in the late afternoon hours may result in a development of convective updrafts reaching a graupel zone and thus, posing a higher probability for the lightning occurrence. Although the moisture content in the vertical profile of the troposphere is not impressive, the presence of almost stationary convective precipitation with superimposing large-scale precipitation of rain and snow (in higher elevations) will pose a risk of the excessive precipitation. NWP models within the forecast period predicts even 100mm over this area.