Storm Forecast
Valid: Tue 30 Sep 2008 06:00 to Wed 01 Oct 2008 06:00 UTC
Issued: Tue 30 Sep 2008 03:12
Forecaster: VAN DER VELDE

SYNOPSIS

Low pressure is in control of the northern half of Europe, with its center near southern Norway. A moist, cool airmass is advected into southern Scandinavia and the Baltic Sea, becoming unstable combined with the warm sea surface temperatures.
A strong jetstream and sea level pressure gradients are present at the southern flank of the low over UK into Germany.
An other area of interest is the Tunisia-Sicily region, where considerable instability coexists with moderate shear conditions.

DISCUSSION

...Denmark, SW Sweden and S Norway...

The eastern North Sea is where GFS predicts the largest instability, and low level buoyancy. Given continuous unstable conditions, steep lapse rates, humid profile with theta-s of 10 degrees over warm sea surface of 16 degrees, waterspouts may appear here and there (see Schleswig, Goteborg and Stavanger soundings of 00Z, as well as Leba and Visby) The Baltic Sea may actually be included, but GFS is not showing much buoyancy there, but a good convergence line.

...Netherlands, northern Germany...

A wave is forecast to pass over this area after 00Z, with a strong PV anomaly behind it. Deep enough instability appears to be associated with it. A threat of a tornado is present, because DLS, LLS and SREH are reaching well into critical values: 30 m/s, 13 m/s and 150 m2/s2 respectively. Marginally severe convective gusts can also occur, around 35 kts (17 m/s).

...Tunisia, Sicily...

A low pressure area affects this region. A high 12 g/kg mixing ratio should be present in the boundary layer, supporting large instability, but 2-4 km lapse rates seem not very steep. Moderate shear (20 m/s DLS, 10 m/s LLS, 200 m2/s2 SREH3) supports organized multicells/MCS and marginal supercells. Chances seem best for large amounts of precipitation, but large hail and waterspouts could occur as well.