Storm Forecast
Valid: Mon 06 Feb 2012 06:00 to Tue 07 Feb 2012 06:00 UTC
Issued: Sun 05 Feb 2012 22:59
Forecaster: TUSCHY

A level 2 was issued for parts of NE Greece mainly for excessive rainfall amounts.

A level 1 was issued for parts of the Ionian Sea, Greece and Aegean Sea mainly for isolated large hail (offshore and along coasts), strong to severe wind gusts and heavy rainfall amounts. Locally excessive rainfall may occur. An isolated tornado is possible mainly along the coasts of Greece.

SYNOPSIS

An highly meridional flow pattern persists over Europe. The main change will be an evolving vortex over the Mediterranean, which develops from the intense longwave trough, centered over CNTRL Europe. At the surface, models converged regarding the developing surface depression. Nevertheless, ECMWF still remains a northerly outlier whereas GFS has the surface depression a bit more to the south. All models however expect a modest strengthening period of that depression with minimum pressure dropping to 995 hPa or below atop the Ionian Sea, before filling over Greece.

Cold and stable conditions persist for the rest of the forecast area ( slightly unstable offshore, but too weak for electrified convection).

DISCUSSION

... Greece, Ionian and Aegean Sea ...

With the vigorous depression atop the Ionian Sea moving slowly to the east, robust moisture advection is expected ahead of that feature, pointing towards Greece. SSTs range from mid to upper tens over the E-Mediterranean and S-Aegean Sea, decreasing to lower tens over the N-Aegean Sea. No serious frontal passage occurred over the E-Mediterranean during the past few days, so not much surprise to see dewpoints in the upper singles/lower tens. With strengthening moisture advection, WAA below 5 km AGL and cool mid-levels, roughly 500 J/kg MLCAPE are expected over the Ionian and Aegean Sea. With aegeostrophic deflection of the LL wind in response to the deepening depression, directional shear increases during the forecast within an unstable warm sector, which shifts from S-Greece (morning) to the Aegean Sea (afternoon hours). Overlap of CAPE and modest speed/directional shear allow organized multicells to evolve with isolated large hail, strong to severe wind gusts and heavy rainfall. The rainfall risk may not be excessive due to the progressive nature of that event, but heavy rainfall may well occur over Greece. Also, an isolated tornado event is possible mainly along the coasts of Greece, before convection becomes elevated onshore.

During the evening hours onwards, round two of enhanced convection will be underway over the Ionian and Aegean Sea, Greece and Cyprus, as cold mid-levels move in from the west. Modest CAPE and weak shear preclude any well organized convection and marginal hail, strong wind gusts and heavy rainfall will be the primary risk. Heavy rainfall is also forecast along the W/SW coast of Turkey. Hence the level 1 was expanded eastwards.

During most of the forecast period, persistent onshore flow occurs within the level 2 area beneath a decent deformation area, which sets up over N-Greece. All models hint on significant rainfall amounts with local model data showing precipitation amounts in excess of 100 mm/24h. Hence we upgraded that part to a level 2 regarding the excessive rainfall risk. The precipitation event gradually weakens during the night as connection to the moisture plume over the Aegean Sea vanishes. Despite the serious rainfall amounts, the run off may be tempered a bit by the change over to snow in higher elevations. Nevertheless, flash flooding is well possible.

... N-Spain ...

Persistent northerly flow affects parts of N-Spain (e.g. Picos de Europa). Abundant moisture moves in from the NW beneath cold mid-levels. Slight destabilization offshore is forecast and a sporadic thunderstorm event can't be ruled out. The main risk will be heavy precipitation along the coast (again, precipitation changing to snow in higher elevations, which may keep run off problems a bit lower). No level will be issued for that event as QPF amounts do not match our criterion.