Storm Forecast
Valid: Fri 06 Jul 2007 06:00 to Sat 07 Jul 2007 06:00 UTC
Issued: Fri 06 Jul 2007 03:16
Forecaster: VAN DER VELDE

SYNOPSIS / DISCUSSION

An unseasonably strong low pressure system with a predicted core pressure of around 984 hPa, deepest at the beginning of the forecast period over NW Belarus, directs a fast-moving cold front northward into an unstable (few hundred J/kg MLCAPE) prefrontal airmass. More than 15 m/s deep layer shear is forecast to be colocated with instability, and more than 10 m/s low level shear. The frontal zone bends back over the Baltic states into Belarus, with also here some instability and moderate shear conditions.

Generally moderate shear and storm-relative flow conditions may aid in organization into strong multicell and short-lived supercell modes, with mostly a threat of large hail in the level 1 region. Storms may stay long in one position or trail over the same region over the Baltic states, with chances of producing local flash flooding.

The level 2 region is where the cold front is oriented perpendicular to the flow. The best instability is forecast here by GFS, while also low level shear over 10 m/s and up to 200 m2/s2 SREH are likely to be available to storms. In principle there exist good chances for supercells, but it is expected that the strong linear forcing creates a long-lived squall line already early in the day. Farther northward of the front is an extra band of SREH, also over Finland, but it seems instability and especially forcing will be insufficient to create storms ahead of the squall line.

Needless to say, the squall line, which may contain bowing segments, poses a main risk of widespread severe gusts, but also large hail and an isolated tornado belong to the possibilities with the stronger and more isolated cells.

Other areas...

Instability over Romania, Bulgaria, Moldova and Ukraine is small and in low shear.

Developing thermal trough over Iberian Peninsula may see the first thundery, high-based convection, GFS parameters suggest, though no convective precipitation. LCL >3000m so isolated dry microburst not ruled out if something develops... as well as wildfire threat created by 'dry lightning'.

Isolated thunder may occur north of the jet axis near northern Netherlands, Germany, Denmark but rather warm cloud tops don't suggest the area is worth highlighting. Farther south some shallow instability under strong shear, expect some linear forced roll convection with low tops, may produce some severe gusts.