Storm Forecast
Valid: Sat 11 Jun 2011 06:00 to Sun 12 Jun 2011 06:00 UTC
Issued: Sat 11 Jun 2011 04:20
Forecaster: VAN DER VELDE
A level 1 was issued for central Sweden and Norway mainly for a chance of excessive convective precipitation.
A level 1 was issued for northern Italy and southern Alpine region mainly for a chance of excessive convective precipitation and isolated large hail.
SYNOPSIS
The weather pattern is messy with several lows on the map, notably an upper low over UK and Netherlands, a surface low pressure area over northern Italy, and large area of weak low pressure extending over eastern Europe and Scandinavia. All are filled with unstable airmasses. High pressure ensures stable conditions over France and the Iberian Peninsula today.
DISCUSSION
...northern Italy and southern Alpine region...
Quite large MLCAPE, ample upper lift and slow storm motion can cause large storms persistent enough to dump excessive amounts of rain in some locations and cause flash floods. The vertical shear is quite weak, but near the mountains likely just strong enough (about 6-10 m/s) to sustain multicell convection.
Isolated large hail may occur.
...central Sweden and Norway...
Storm motion parallel to a boundary may cause training cells with a slight potential of producing excessive rain, also aided by orographic moisture lifting. Near this boundary is also enhanced shear and SREH (100-200 mē/sē) but most is to the south, offset from the unstable air. Nonetheless, sufficient shear could exist for maintaining multicellls.
...UK, Benelux, Germany...
Vertical wind shear is mostly weak today in Europe, except over the Benelux/German region, but this is confined mostly to the higher levels(>6 km, 15-25 m/s) and parallel to the cold front in N Germany. Over Germany also in mid levels there is good shear, but MLCAPE values are rather marginal there (some 150 J/kg), reducing large hail chances. Low level shear (0-1 km) is too weak anywhere for tornadoes, although under the UK/NL upper low isolated spout-type tornadoes/funnel clouds could develop. This is aided by moist profiles, weak flow, and steep low-level lapse rates and low-level CAPE.
