Storm Forecast
Valid: Thu 19 Mar 2015 06:00 to Fri 20 Mar 2015 06:00 UTC
Issued: Thu 19 Mar 2015 02:05
Forecaster: GATZEN

SYNOPSIS

Two nearly stationary cut-off lows are present to the south-west of the Iberian Peninsula and across Romania/Bulgaria. Another small cut-off moves from the Benelux countries to western France. A zonal ridge axis extends from the British Isles to the southern Baltic Sea into Russia, another ridge is located across the western and central Mediterranean. At lower levels, polar air masses affect most of Europe, except for a plume of African air spreading into the west Mediterranean. Low-level moist air will be located across south-western Europe, where steep lapse rates are expected and CAPE is forecast.

DISCUSSION

Spain

At the eastern flank of the cut-off low, a plume of well-mixed desert air spreads into the west Mediterranean and also into eastern Spain. West of the warm front, a moist polar air mass is present, allowing for some thunderstorms near the base of the cut-off. Current thinking is that deep moist convection is suppressed by a capping inversion in the warm advection regime. The potential increases late in the period, when a vort-max ejects from the southern base of the cut-off and moves eastward across southern Spain. Large-scale lift will reduce the cap across an area with low-level moisture convergence overlapping with an elevated mixed layer. Initiation is uncertain, but upslope flow and frontogenetical forcing east of an approaching cold front can lead to sufficient lift. If persistent storms manage to form they will have a potential to become severe given favourable veering profiles and strong vertical wind shear around 15 m/s in the lowest 3 km. However, the chance of surface-based storms is quite limited over Spain due to low-level cooling during the night hours. Therefore, no threat level is issued.