Storm Forecast
Valid: Thu 21 Feb 2013 06:00 to Fri 22 Feb 2013 06:00 UTC
Issued: Wed 20 Feb 2013 18:16
Forecaster: GATZEN

A level 1 was issued for the south-east Mediterranean mainly for large hail.

A level 1 was issued for the south Iberian Peninsula mainly for tornadoes.

SYNOPSIS

Cold and dry air masses are present across northern and central Europe through-out the period. Southern Europe is affected by the polar jet stream. A deep lifting trough will move north-eastward during the period reaching Greece on Friday morning. Upstream, a short wave trough will rapidly cross the Iberian Peninsula during the night hours. Ahead of these features, low-level moisture exceeding 8 g/kg low-level mixing ratio will advect north-eastward.

DISCUSSION

East Mediterranean

A deep trough currently centred across Algeria will move north-eastwards during the period. Ahead of this trough, QG forcing will likely result in large-scale lift. The affected air mass is dry and cold at low levels as indicated by latest observations, and stable conditions are expected initially.

Mid-level lapse rates will likely increase especially after Thursday evening when the trough center moves across the Aegean Sea while low-level warm air advection will continue. Additionally, models indicate rapidly increasing boundary-layer moisture near the warm front with low-level mixing ratios of about 8 g/kg. Although this moisture increase is somewhat questionable, some instability may result on Friday morning especially at mid-levels.

As a consequence, some thunderstorms are expected on Thusday starting near Sicily and spreading eastward into the south Aegean on Friday morning. Given the strong deep layer vertical wind shear exceeding 25 m/s, multicells and supercells are not ruled out. Limiting factor will be the rather stable boundary-layer and associated widespread precipitating clouds. However, isolated large hail events may be possible.

Iberian Peninsula

An intense short-wave trough and associated strong mid-level jet streak will enter Iberia on Thursday afternoon, leading to strong QG forcing. A tongue of rich low-level moisture will spread into southern Portugal and Spain ahead of this trough. Lapse rates are rather poor and CAPE is very limited.

However, daytime heating may result in CAPE during the afternoon hours across southern Portugal and Spain, and some thunderstorms may develop. Storm that form may organize into multicells given the strong vertical wind shear exceeding 15 m/s in the lowest 3 km. Additionally, some mesocyclones may form. These may produce an isolated tornado given the strong low-level shear. Limiting factor will be the weak CAPE. During the night hours, low-level cooling will result in decaying storms.