Storm Forecast
Valid: Thu 10 Dec 2015 06:00 to Fri 11 Dec 2015 06:00 UTC
Issued: Thu 10 Dec 2015 06:12
Forecaster: GATZEN

A level 1 was issued for southern Sicily mainly for large hail.

A level 1 was issued for western Norway mainly for excessive precipitation and to a lesser extent severe wind gusts.

SYNOPSIS

The active zonal flow continues across northern Europe. A strong jet streak travels across the British Isles into southern Scandinavia. At its southern flank, ridging takes place and a central European trough cuts off into the central Mediterranean.

DISCUSSION

Tyrrhenian into Ionian Sea

The cut-off will provide DCVA across the Mediterranean today, leading to steepening lapse rates as indicated by latest Ajaccio sounding. Given relatively rich low-level moisture of around 6 g/kg in the lowest 500 m overlapping with the evolving lapse rates due to latest GFS model runs, thunderstorms are expected to spread south-east ahead of the trough axis. As strong north-westerly mid-level winds overlap with the region of storms, deep layer vertical wind shear will be around 20-25 m/s, allowing for storm organization. Multicells are expected that can be capable of producing some large hail. The threat is only weak, though, and a risk level is not issued over most places. Best chances are forecast across Sicily, where a small level 1 is introduced. Storms will spread into the Ionian Sea during the period, where Greece may be affected by excessive precipitation, but convective contribution is expected to be weak and a level 1 is not issued.

Northern British Isles to south-western Norway

Numerous showers and thunderstorms are expected to spread east at the cyclonically sheared flank of the mid-level jet streak. Vertical wind shear is weak over the sea and storm organization is limited to some bowing lines especially near the coasts. However, given about 20 to 25 m/s wind speed at 850 hPa, severe wind gusts are possible. Additionally, excessive rain is expected along western Norway due to ongoing convective activity until the end of the period.