Storm Forecast
Valid: Tue 01 Jan 2008 06:00 to Wed 02 Jan 2008 06:00 UTC
Issued: Mon 31 Dec 2007 15:13
Forecaster: DAHL

SYNOPSIS

An upper low, located over S Scandinavia on Monday evening, is simulated to expand southwards into the S Balkans on Tuesday, thereby becoming increasingly elongated, while north of it, an upper cut-off anticyclone is developing over N Scandinavia. This feature will reinforce SFC anticyclogenesis over NE Europe, so that a large and intense area of high pressure will sprawl into most of Europe, providing the continent with dry and cold polar continental air masses. Weak low pressure will persist over the Ionian and Aegean regions. An upper Atlantic cut-off cyclone with an attendant SFC low are expected to reach the W Iberian Peninsula on Tuesday afternoon/evening.

DISCUSSION

... western Iberian Peninsula ...

Ahead of the Atlantic low-pressure system, a plume of moist and weakly unstable air will be advected across western Iberia late in the period. Given strong warm advection as well as quite stable LL lapse rates, storms will likely tend to be elevated and imbedded in stratiform rain. Minimal / partly non-existent instability should, in addition, limit the thunderstorm coverage. There seems to be a slight chance of small supercells, should the convection become SFC-based, given rather intense shear profiles. These cells would have fair potential for spawning a brief tornado or two.

In the wake of the warm-air tongue, deeply mixed polar air will reach the NW parts of the peninsula late Tuesday night/early Wednesday morning. These storms will likely be SFC-based and still profit from strong LLS, though DLS will be decreasing ... still, a slight chance for an isolated coastal tornado or two appears to exist.

A marginal level-one threat will be introduced over NW Portugal and extreme NW Spain, since these locations will be affected by both regimes (pre- and post-frontal).

Otherwise, severe-thunderstorm potential should be negligible.