Storm Forecast
Valid: Sun 24 Feb 2008 06:00 to Mon 25 Feb 2008 06:00 UTC
Issued: Sat 23 Feb 2008 20:01
Forecaster: TUSCHY

SYNOPSIS

A fragile omega pattern over the Mediterranean has established but is in evidence in upper-level streamline maps. Framed by two troughs one over SW Europe and the other over SE Europe, ridging is present over Italy and Germany with unseasonably warm conditions. A belt of strong westerlies covers most parts of N-Europe but only one depression is of interest . This feature moves onshore over N-Norway with a low-end thunderstorm risk.

DISCUSSION

.... Parts of Portugal and Spain ....

Downstream of a decaying upper-level trough just west of Portugal winds at all levels turn on southerly directions during the morning hours, but veer somewhat in the mid-levels during the early afternoon hours onwards. Main reason for this wind shift is the highly positive tilt of upper-level trough, centered over Portugal during the afternoon hours. Main concern for an isolated severe weather risk arises along the Strait of Gibraltar and north / northeastwards. Strongest warming / cap looks like to be displaced to the east and despite limited diabatic heating, surface temperatures in this area should soar into the mid-tens. In addition, current dewpoints are already good and after the end of easterly winds ( e.g. Levante-event in the Strait of Gibraltar ) during the morning hours an onset of southerly winds will push another surge of moist air northwards, increasing dewpoints 1-2°C ( e.g. Granada sounding ). Forecast soundings in this area hint on deep convection, steep LL lapse rates and strong veering at lowest levels. Despite the already uncapped airmass a modest mid-level speed max approaches from the west, placing the area of interest under the left-exit region.
Overall degree of shear is not impressive, but low or slightly lifted LCLs and combination of veering and maximized 0-3km instability release could be enough for an isolated funnel / short-lived tornado and large hail report. We want to highlight this area in such a broad general thunderstorm area and increased probabilities to a low-end level-1. Severe weather / Thunderstorms will diminish after sunset.

Regarding thunderstorm coverage, the main activity will be confined to S-Portugal and extreme SW-Spain. There will be a flash flood risk as steering flow is weak, airmass quite moist and a persistent 15m/s LLJ points to the coast of Portugal for a prolonged period.

....Norway and Sweden....

For Sweden, there will be a marginal thunderstorm risk between 06Z and 12Z as WAA is underway, resulting in steep mid-/upper-level lapse rates and some low-end elevated instability release. Some forcing is present and an isolated elevated thunderstorm could occur. Right now streamline pattern is too diffluent and no compact UVV field is present in the past model runs and hence we went with no thunderstorm area.

A few more thunderstorms could develop along the west coast of Norway but ELs are warmer compared to the past few events and no thunderstorm area will be issued.

Severe gusts will occur along the coastal areas of N-Norway but there are no hints on deep convection in this area so not even a non-thundery level-1 area will be issued.