Storm Forecast
Valid: Mon 08 Mar 2010 06:00 to Tue 09 Mar 2010 06:00 UTC
Issued: Sun 07 Mar 2010 19:57
Forecaster: DAHL

A level one was issued across the Ionian and Aegean regions for marginally severe wind gusts and excessive convective rainfall.

A level one was issued across the western Mediterranean Sea for marginally severe wind gusts and excessive convective rainfall.

A level one was issued across the southern Iberian peninsula for excessive convective rainfall.

SYNOPSIS

Most of the European continent is dominated by a sturdy high-pressure area, filled with continental polar air masses, reaching well into the Mediterranean regions. A marked air-mass boundary exists between these polar air masses and moist subtropical air over the Mediterranean. This boundary should stretch from southern Iberia eastward across the Aegean regions into the Black-Sea area on Monday afternoon. The main upper frontal zone is aligned with the low-level thermal boundary. Several imbedded vorticity maxima will support SFC cyclogenesis along the SFC front, resulting in a southward shift of this front over the western Mediterranean regions late in the period.

The subtropical air south of the boundary is essentially moist-neutrally stratified, with weak CAPE indicated by the models ahead of the upper vorticity maxima.

DISCUSSION

... Ionian and Aegean regions ...

Ahead of the low-pressure system that will reach the Aegean region late in the period, steep mid-level lapse rates from the Sahara desert will be integrated into the circulation (per GFS). Comparatively weak low-level moisture should limit the overall destabilization, however, so that CAPE will be unlikely to exceed a few 100 J/kg.

GFS simulates a rather patchy CAPE field, as well as several rather small-scale bulk-shear maxima, with transient/partial overlaps of maxima of both fields. This suggests that the average DLS may be somewhat limited, but temporarily become favorable for storm organization.

Although the majority of the cells will likely be rather weak, some of them may organize into line segments and mesocyclonic storms. The main threat should be marginally severe outflow winds, though small hail and maybe a brief tornado or two cannot be excluded, especially in coastal regions. Heavy and prolonged, convectively-augmented rain may occur especially in upslope-flow regimes over the southern Balkan States.

... western Mediterranean regions ...

A somewhat weaker cyclone will exist farther upstream over the western Mediterranean. Given the lack of steep lapse rates, the convective threat should be considerably smaller than with the system farther east. However, 25 m/s DLS suggest that rather well-organized (albeit comparatively small) multicells and also mesocyclonic storms may develop, posing a threat primarily of severe wind gusts. Especially in the WAA regime of the cyclone, convectively-augmented precip may exceed severe probabilities.

... southern Iberian peninsula ...

Yet another SFC low, reaching the Iberian Peninsula late in the day, will affect the forecast region on Monday. This system accomodates quite moist subtropical/Atlantic air masses in its warm sector. Although instability will likely be minimal, it is anticipated that weak and probably elevated convection will be imbedded in warm- and cold-frontal rain bands. Strong mesoscale ascent should support large amounts of precip over the southern portions of Iberia, which will likely exceed LVL1 criteria. Shear profiles will be supportive of severe evolution, but it does not seem that deep SFC-based convection will form.