Storm Forecast
Valid: Sun 29 Jul 2007 10:00 to Mon 30 Jul 2007 06:00 UTC
Issued: Sun 29 Jul 2007 10:17
Forecaster: DAHL

SYNOPSIS

Rather intense upper vort max is roundig the base of a quasi-stationary large-scale upper low which is centered over Scandinavia. This vort max will cross central Europe during the remainder of the period. Attendant to this feature is a wave cyclone, with the trailing cold front forecasted to curve from E Poland across Hungary into the pre-Alpine regions by Monday 06Z. Ample NWLY flow is epected in its wave in deep polar air mainly over the Benelux countries and Germany.
Otherwise ... quite warm but relatively dry air lingers over southern and eastern parts of Europe under largely quiescent SFC conditions.

DISCUSSION

... central Europe ... N Mediterranean ...

It does not seem that significant deep convection will develop in association with the central European frontal wave as GFS consistently fails to simulate deep instability along the front. Narrow/shallow lines of convection have formed along the cold front and in the warm sector in the past hours, however, and vertical motion in these lines could become strong enough to maintain sufficient charge separation for scattered lightning. However, best chance for SFC-based convection seems to exist along the front over eastern France in the evening hours. Shear profiles should be well sufficient for organized convection, including marginally severe hail, severe wind gusts and also the chance of tornadoes given 10 m/s LLS. The tornado threat will likely decrease towards the east where LLS will be weaker ... still, a few marginally severe hail events are conceivable also over NW Italy.

In the wake of this system, more or less cellular polar air convection will likely overspread the NRN parts of Germany in the evening hours, but it seems that loss of daytime heating will limit the CAPE, so that it appears somewhat unlikely that siginificant convective activity will develop, though a couple of strong showers, maybe weakly electrified, capable of strong wind gusts may well occur.

... Baltic-Sea region ... North-Sea coast ...

Latest soundings from the Baltic Sea region reveal nearly a saturated boundary layer and rather steep SFC-based lapse rates, resulting in strong low-level buoyancy. It seems that LL shear is somewhat strong for widespread waterspouts, still the thermodynamc profiles suggest that at least isolated spouts are possible. The chance of water spouts initially extends into the North-Sea coasts of N Germany and the Netherlands, but should gradually decrease there as the low-level flow increases. The water spouts may well occur outside the hunderstorm area with relatively shallow, non-electrified convection.