Storm Forecast
Valid: Tue 26 Jun 2007 06:00 to Wed 27 Jun 2007 06:00 UTC
Issued: Tue 26 Jun 2007 09:58
Forecaster: VAN DER VELDE

SYNOPSIS

An unseasonably strong low pressure area over southern Scandinavia affects the Netherlands, northern Germany and Poland today with strong pressure gradients, which may result in damaging gusts (given 50 kts at 925 hPa), especially to trees. The cold front of the low is moving from Poland-Austria into Baltic States, Belarus and Romania, where the airmass in the warm sector is very unstable in addition to strong deep layer shear.

DISCUSSION

...NE Italy, northern Balkan into Ukraine, Belarus, Lithuania...

Due to absence of proper GFS fields and recent NMM, confidence of instability release is lower than usual.
However, 00Z soundings of Udine, Zagreb, Cluj-Napoca and Chernivtsi have indicated an unstable environment that can result in deep convection if the currently observed dewpoints of 16-20C are put into it... especially those around 20 degrees in the level 2 region should make some 1000 J/kg MLCAPE that can be released by forcing at the cold front or in a prefrontal convergence zone.

With the proximity of the jet, will maintain deep layer shear in the order of that indicated by 00Z hodographs: 20-30 m/s vectors over 0-6 km. Older NMM run indicates a maximum of SREH in northwestern Romania. The northern parts of the level 1 are more favorably positioned with respect to the jet exit and should see moderate deep layer shear and possibly better low level shear as 850 hPa winds are stronger to the north.

Convective developments are likely to organize into supercells all over the level 1 area, featuring (very) large hail and an isolated tornado, with rapid development into a squall line over northern parts of the area (Lithuania into Ukraine) with a threat of widespread severe gusts.


...Germany and Poland...

Instability has been indicated by GFS to occur in the sunny zone between cold front and back-bent occlusion. Convection will grow in a zone with decent low level shear due to high windspeeds at 850-925 hPa (45-65 kts). Severe convective gusts are likely, especially if storms will group into a line. Though deep layer shear likely circles around this area as it usually does, a small region may profit from the shear and shallow mesocyclones may occur in storms, with a possible tornado as result and perhaps marginally severe hail.