Storm Forecast
Valid: Thu 19 Nov 2009 06:00 to Fri 20 Nov 2009 06:00 UTC
Issued: Wed 18 Nov 2009 22:06
Forecaster: GATZEN

SYNOPSIS

In the wake if an intense short-wave rough, a broad high amplifies over Europe. A weak cut-off low will move eastward across Iberia, while another long-wave trough approaches west of Europe. It will affect the British Isles late in the period. At lower levels, relatively warm air masses spread into western, central, and northern Europe, and cool low levels will likely lead to stable conditions.

DISCUSSION

Eastern Europe

Weak instability due to rather moist maritime air masses will spread into eastern Europe in the range of the short-wave trough. Given the weak low-level heating, deep moist convection is rather unlikely. The best potential exists at the end of the period to the north of the Black Sea, where relatively warm and moist air masses may spread northward at low levels, increasing the instability. A few thunderstorms may form in this region along the cold front east of the forecast region. Rather weak vertical wind shear and instability are expected to limit severe potential.

Southern Iberia and northern Morocco, Algeria

In the range of the cut-off low, weak instability will likely develop due to rather cool mid-level air masses over the warm sea surface. Models indicate some moisture with low-level mixing ratios around 8 g/kg and low-level convergence underneath the trough centre. Lift due to DCVA is expected to weaken the cap, and thunderstorms are forecast. Severe thunderstorms seem to be not very likely as the vertical wind shear is limited near the trough centre. However, the deep layer vertical wind shear will be slightly stronger in the range of the jet streaks curving around the cut-off low, and an overlap of weak instability and strong DLS may be possible over the north-African coast. Rotating updrafts may evolve, but the chance of large hail and severe wind gusts seems to be too low for a risk level.

Ireland

At the end of the period, some thunderstorms may spread into Ireland in the range of the trough axis of the approaching Atlantic trough. Latest models do not expect very strong low-level vertical wind shear and only marginal CAPE, limiting the chance of organized convection significantly.