Storm Forecast
Valid: Sat 15 Nov 2008 06:00 to Sun 16 Nov 2008 06:00 UTC
Issued: Fri 14 Nov 2008 18:59
Forecaster: DAHL

SYNOPSIS


Rather intense, meandering upper westerlies are covering the northern and eastern parts of Europe. Feature of most interest in this flow regime will be the trough to be expected off the Scandinavian W coast at the beginning of the period. This feature will lift northeastwards during the period but in doing so, maintain strong cyclogenesis over the North Sea and southern Scandinavia. Over the central Mediterranean, a quasi-stationary upper cyclone persists through the period.

DISCUSSION

... Baltic region ... S Sweden ...

It appears that strong slab ascent along the cold front associated with the Scandinavian trough will be accompanied by a narrow/shallow convective line, mainly affecting the Baltic Sea and the Baltic States, but later also N Germany and N Poland, with the convection becoming increasingly shallow towards the southwestern extension of the front. It is quite likely the this convection will be associated with very gusty winds as a result over vertical momentum transport, and so will mainly act to augment the strong/severe large-scale gradient flow. Near the apices of line segments, the strong vertical shear may be tilted into the vertical, so that mesocyclones/MCVs may form, which could spawn a brief tornado or two, though the background helicity is not extraordinarily strong per latest model guidance. Though CAPE signals are quite weak, sufficient confidence in convective development exists, necessitating a level one treat. Lightning activity should be confined to the deeper segments of the line over S Scandinavia and the Baltic region.

... central and western Mediterranean ...

Some instability will likely persist over the central Mediterranean underneath the upper thermal low, and in its periphery where a plume of wrap-around theta-e is present. Not the entire region where convection is expected, will benefit from vertical shear, but about 20 m/s 0-6 km bulk shear should be present over the Ionian Sea, S Italy, and the southern Adriatic Sea. Steepening lapse rates and increasing low-level shear are simulated over the Ionian Sea in the evening hours.

Thinking is that thunderstorms will persists throughout the period, with highest chances of organized thunderstorms existing over southern Italy, the S Adriatic, and the S Ionian Sea, where kinematic support will be best. Expect isolated marginally severe hail along with severe wind gusts with the strongest of these storms.
As thermodynamic and kinematic fields strengthen over the Ionian Sea towards the evening, more intense severe weather, including tornadoes may occur.

Farther west, where shear profiles are weaker, strong low-level lapse rates are anticipated, hinting at the possibility of non-mesocyclonic tornadoes. These should be too isolated in nature to warrant a categorical outlook for this phenomenon.