Storm Forecast
Valid: Thu 06 Nov 2008 06:00 to Fri 07 Nov 2008 06:00 UTC
Issued: Wed 05 Nov 2008 22:16
Forecaster: GATZEN

SYNOPSIS

As the geopotential over northern Atlantic weakens, cut-off low over west Mediterranean starts to move north-eastwards. While quite cool air mass is present in the centre of this trough, warm air mass is advected northward over central and east Mediterranean into the Balkans. A ridge extends from east Mediterranean to eastern Europe and Scandinavia, while a cold arctic trough spreads into Russia.

DISCUSSION

Southern Italy, Adriatic

Latest satellite images indicate intense convection over southern Italy in the range of a strong low-level jet situated ahead of the cold front of the west-Mediterranean trough. During the forecast period, this system will slowly move eastwards, while the axis of a negatively tilted short-wave trough will enter central and southern Italy. Latest soundings from the low-level jet indicate winds in excess of 15 m/s at the 950 hPa level and quite moist low-level air mass, resulting in approximately 1000 J/kg CAPE at the northern nose (Zadar). Region of strongest instability will likely spread eastward into southern Adriatic and southern Italy later on, given rather high boundary-layer moisture and decreasing 850 and 700 hPa geopotential and temperature. On THU, latest GFS indicates intense lift ahead of the approaching trough axis, and thunderstorms will likely develop. Limiting factor is relatively weak convergence along the frontal boundary, and current thinking is that one or two multicells will likely grow into MCSs moving into southern Adriatic later on. Chance for severe convection is expected to be not very high as mid-level winds seem to be quite weak. However, strong low-level winds may produce some severe downburst wind gusts along the leading convective line. Additionally, slightly veering profiles especially near southern Italy seem to be favourable for tornadoes. Limiting factor is again weak low-level convergence. Large hail is not ruled out, while intense rain spreading into Balkans later on will pose a significant threat.

Ireland

In the range of the trough centre of Atlantic low, models indicate cold mid-level air mass that will likely be unstable above the warm sea surface. Low-level convergence near the trough centre, quite moist low-level air mass and rather steep lapse rates are expected to be sufficient for deep convection. Severe wind gusts will likely be possible given strong synoptic winds.