Storm Forecast
Valid: Tue 07 Dec 2010 06:00 to Wed 08 Dec 2010 06:00 UTC
Issued: Mon 06 Dec 2010 21:48
Forecaster: KOROSEC

A level 1 was issued for much of Iberia mainly for excessive convective rainfall and to a lesser extent for severe wind gusts, hail and tornadoes.

SYNOPSIS

Placed between strong ridges over Altantic and Russia, a large-scale upper trough remains almost stationary during the forecast period over much of northern and central portions of Europe. On its SW-ern edge, rather deep low maintains itself and constantly pushing warm/unstable airmass into the Iberian Peninsula.

At surface, a frontal zone separating warm subtropical airmass from the colder polar airmass, stretches from central Iberia NE-wards across the Alps towards eastern Europe.

The rest of Europe will experience conditions not favorable for deep convection. Though, sporadic lightning strikes cannot be excluded in the shallow convection along the western coast of Norway where very cold upper levels (below -40°C) will create very steep lapse rates over the sea.

DISCUSSION

... Iberia ...

Placed under rather cold upper levels, surface low remains quite stationary during the morning hours and finally makes some progress eastwards later towards Wednesday. It maintains its strength with persisting warm and humid air advection into SW parts of Europe. At mid-levels, quite strong jet wraps around the trough axis with strong deep layer shear in excess of 25-30 m/s. It seems that veering profiles will also enhance LL shear/SREH (above 15 m/s of LLS and above 200 m^2/s^2 of SREH3). Models are confidently simulating several hundreds J/kg of MLCAPE.

It seems that persisting SW flow and large-scale ascent will be favorable for extensive rainfall across much of Iberian Peninsula, resulting in high rainfall accumulations. However, placed in rather unstable and sheared environment, numerous embedded organized storms, including severe storms, seem likely as well. The main threat will be excessive convective rainfall locally, especially where it will combine with persisting/maintaining orographic effects (SW Iberia). Additionally, high SREH/shear values suggest that rotating storms are possible, bringing marginal threat for strong winds, small hail or even tornadoes especially along the coastal areas. High shear could also support training effect of the storms and enhance flash floods threat additionally.

However, high-end level 1 threat has been issued for much of Iberia, but it might need to be upgraded into level 2 in case of larger coverage or severe storms with intense rain.