Storm Forecast
Valid: Sat 31 Jan 2009 06:00 to Sun 01 Feb 2009 06:00 UTC
Issued: Fri 30 Jan 2009 18:06
Forecaster: DAHL

SYNOPSIS

An omega-like upper flow pattern is present over Europe at the begininng of the period, with an Atlantic upper trough over the Iberian peninsula and another, broader trough over SE Europe. In between, over Scandinavia, there exists a quasi-stationary upper ridge. The Iberian upper trough will close off into a cut-off cyclone and undercut the ridge as it travels into the central Mediterranean ... supporting a westward motion of the SE-European upper low. Another, rather intense upper low will affect W Iberia late in the period.
At the surface, the main features are a deep high-pressure region over E Europe and Russia, and a deep/large Atlantic low-pressure system associated with the trough reaching W Europe late in the period. The preceding Mediterranean upper feature is accompanied only by a weak low-level cyclone in the current simulations.

DISCUSSION

... Portugal ... extreme NW Spain ...

Some potential for severe convective evolution appears to exist along and ahead of the cold front associated with the system that reaches Portugal early Sunday morning. Main issue will be the minimal degree of instability. GFS has been somewhat inconsistent over the past runs regarding the depth of the simulated convection. DLS is in excess of 35 m/s, with LLS exceeding 15 m/s over Portugal. This, and the presence of strong upward forcing, suggests that even with minimal instability, organized convection may occur. Current thinking is, that comparatively short-lived, linearly-organized convection will occur, posing a threat of damaging wind gusts and an isolated tornado or two, given anticipated minimal capping, almost saturated low-level air and ample low-level shear.

The threat is quite conditional upon the presence of SFC-based instability, and even if convection occurs, it may tend to be slightly elevated. Still, confidence in the above scenario is sufficiently high for marginal level-one threat area.

... western Mediterranean ... Tyrrhenian and W Ionian Sea ...

Scattered thunderstorms will likely accompany the upper low that moves from Iberia across the W Mediterranean on Saturday. Degree and depth of instability are expected to be quite marginal, so lightning activity may be somewhat sporadic in nature. Kinematic and low-level thermodynamic fields suggest that the threat for severe thunderstorms, including waterspouts, will be quite low with this activity. It is challenging to pinpoint those areas where lightning activity will be maximized amidst a relatively large area exhibiting marginal conditions. Have thus placed the thunderstorm areas where GFS suggests that EL temperatures will be lowest.

... E Ionian Sea ... SW Greece ...

A peripheral vort max associated with the SE-European upper long-wave trough will affect the Aegean region early in the period, which should allow instability to become deep enough for sporadic lightning. It seems that best chances for thunderstorms will exist over the eastern Ionian Sea and the Greek SW coast early in the period. Shear profiles as well as kinematic fields do not suggest that an appreciable severe-thunderstorm threat exists.