Storm Forecast
Valid: Mon 18 Sep 2006 06:00 to Tue 19 Sep 2006 06:00 UTC
Issued: Sun 17 Sep 2006 19:35
Forecaster: GROENEMEIJER

SYNOPSIS

Monday at 06:00 UTC the flow across Europe is characterized by a broad area of low pressure centered over the northern Adriatic, a weak ridge upstream over Spain and France, and an approaching trough about 300 km W of Ireland, preceded by a frontal system.

DISCUSSION

Ireland, SWrn Scotland

A strong SWly flow is expected to overspread as a slowly occluding system moves eastward over the British Isles. The system is followed by an intense trough at mid-levels and only weak cold air advection, leading to strong quasigeostrophic forcing for upward vertical motion. Destabilization is expected as a result, leading to a few 100's of J/kg CAPE forming over Ireland and the Irish Sea. Strong low-level bulk shear of 10-15 m/s in the 0-1 km layer, and strong deep-layer shear, suggest that short-lived rotating updrafts are possible and that a threat of one or two tornadoes or waterspouts will be present. Additionally, hail exceeding 2 cm in diameter and severe wind gusts may locally occur. The severe weather threat is expected to spread eastward across the level 1 area, during the late morning hours and diminish during the evening.

Adriatic and Tyrrhenean Seas

A surface low pressure centre is expected to move slowly eastward over the northern Adriatic Sea. Near and south of the low's centre, lapse rates are expected to be slightly steeper than moist adiabatic over sea surfaces. Winds should be weak and high relative humidities are expected, resulting into low LCL heights. Convective storms are forecast over much of the Adriatic Sea, particularly the western Balkan and Greek coasts and the southern Tyrrhenean Sea. The aformentioned weak winds, low LCL heights and anticipated convective development suggest that a risk of waterspouts will exist. Those may naturally move onshore every now and then. The risk is expected to persist during the entire forecast period.