Storm Forecast
Valid: Thu 17 Nov 2016 06:00 to Fri 18 Nov 2016 06:00 UTC
Issued: Wed 16 Nov 2016 19:52
Forecaster: GATZEN

SYNOPSIS / DISCUSSION

Intense polar trough expands across north-western Europe. Strong mid-level flow spreads into the southern British Isles and central Europe, with a PV intrusion moving south, extending from northern France to north-west Germany by Thursday, 6 UTC. At lower levels, atmospheric river brings Atlantic moisture into France and Germany, with dew points about 8 to 12°C. It will partly overlap with the PV intrusion from northern France into northern Poland, and low-level lapse rates increase is expected due to stretching. Weak instability can form with equilibrium level temperatures slightly below -15°C. Current thinking is that a narrow cold-frontal rain band evolves that could produce some lightning. Intense deep moist convection is not expected given rather weak low-level convergence, warm EL temperatures, and weak CAPE. Strong to severe non-convective wind gusts are expected. Tornadoes are not ruled out. However, weak low-level convergence and limited low-level buoyancy limit the risk despite strong low-level shear. High winds can be expected especially over the North Sea region south of a developing surface cyclone.

In the wake of the surface low, a deeply mixed maritime air mass affects the British Isles. Showers and thunderstorms are expected. Limiting factor is weak low-level moisture. Given strong low-level vertical wind shear, brief tornadoes are not ruled out.

The Mediterranean is affected by a weak ridging to the north of a well-developed cut-off low centred over Algeria. Best low-level moisture is situated over the south-west Mediterranean thanks to the warm sea surface and low-level convergence in the range of the cut-off low. Dry northerly flow continues over the northern and eastern Mediterranean Sea. Lapse rates are relatively poor even close to the trough centre. Thunderstorms are expected from the Tyrrhenian Sea towards Algeria and Tunisia. Vertical wind shear is limited to 10-15 m/s in the lowest 6 km, allowing for some multicells and brief hail. Waterspouts are not ruled out as well.