Storm Forecast
Valid: Thu 07 Jan 2010 06:00 to Fri 08 Jan 2010 06:00 UTC
Issued: Wed 06 Jan 2010 20:50
Forecaster: GATZEN

A level 1 was issued for southern Iberia and north-western Africa mainly for excessive rain.

A level 1 was issued for the north Mediterranean mainly for excessive rain.

SYNOPSIS

Initially, a strong westerly jet stream affects the Mediterranean at the southern flank of low geopotential over Europe. An intense vort-maxima actually over the British Isles is expected to amplify into the Iberian Peninsula during the period, leading to a stong south-westerly flow and warm air advection over the central and eastern portions of the Mediterranean. Caclogenesis and excessive rain are likely across the Mediterranean. To the north, rather dry and stable polar air masses will remain at low levels, suppressing deep moist convection.

DISCUSSION

Iberia region

In the range of the short-wave trough that spreads into the Iberian Peninsula, strong cold air advection is expected. A surface cold front is forecast along the southern portions of Spain on Thursday morning that will move south-eastwards. To the south of this front, latest observations indicate rather rich low-level moisture. Given strong lift ahead of the trough, this air mass will likely become unstable, and deep moist convection is likely along and north of the cold front. Given the vertical wind shear of around 10 m/s in the lowest levels, embedded mesocyclones are not ruled out, but the chance seems to be rather low. A brief tornado may evolve when mesocyclones will indeed develop. Over northern Africa, the chance of tornadoes is higher given stronger vertical wind shear and veering profiles. Excessive precipitation is forecast to the north of the cold front as well as along the western coasts where upslope flow is present.

Further north, a deep cold air mass spreads across the Bay of Biscay region. Models suggest rather steep lapse rates over the warm waters and deep moist convection may form. Main limiting factor will be rather dry low-level air, but thunderstorms will be likely along the southern portions of Spain.

North Mediterranean

With the strong westerly flow, a short-wave trough moves eastward and crosses the Balkan region. Upslope flow of rather moist low-level air and weak instability will likely favor showers and thunderstorms that may be capable of producing excessive rain along the coasts in initially. Later in the period, the low over Iberia moves into the north-western portions of the Mediterranean, leading to warm air advection and thunderstorms along the cold front. Strong vertical wind shear will be favorable of embedded mesocyclones, and a brief tornado is not ruled out. Excessive rain is forecast especially along the wavy cold front.