Storm Forecast
Valid: Sun 16 Jun 2013 06:00 to Mon 17 Jun 2013 06:00 UTC
Issued: Sun 16 Jun 2013 03:43
Forecaster: VAN DER VELDE

A level 1 was issued for France mainly for large hail.
A level 1 was issued for Alpine regions to Czechia mainly for large hail.

SYNOPSIS

A low pressure system over southern Scandinavia dominates the north side of the map with convective conditions in the cool airmass. Its cold front moves in the late morning and early afternoon into Latvia, Estonia and southern Finland. At 03Z It curves all the way back to Czechia and westward to western France with cool air at the north side. But the thermal boundary slowly starts to assume warm frontal characteristics. The main driving force is an active low SSW of Ireland which sets up a southerly low level flow over Iberia and France, quickly advecting warm air to the north. By the end of the forecast period the warm air reaches Belgium.
As is common in the onset of these situations, GFS and WRF models quickly produce strong low.level moisture out of nowhere, resulting in dewpoints over 20°C and SBCAPE values soaring to 1500.-2500 J/kg. In reality the moisture increase is not so dramatic and takes more time. The advection of steep lapse rates suggests CIN will limit the extent of convective development. There is only weak low-level forcing present over central France and eastward, so that local orography is almost the only triggering factor. With the exception of western France during the night.

DISCUSSION

...southern Scandinavia, Baltics...

Near the center of the low, cell motion is slow, shear is weak and capping absent. Typically land/waterspout type tornadoes are observed under such conditions. A vorticity maximum is produced by GFS at the southeast coast of Norway which may be a focus for spin-up.
The cold front over the northern Baltic region can produce convective wind gusts but likely not severe, also low.level shear can be locally marginally favorable for a isolated tornadic event.

...France...

Taking into account inflated moisture in GFS the chance of storms is estimated lower, but even ECMWF produces decent CAPE. Triggering of a few storms is likely over the Massif Central, which given the 15-25 m/s 0-6 km shear and 100-200 m²/s² 0-3 km SREH can develop into supercells. Large hail is then the primary threat.
Over western France an elevated MCS can likely be initiated early on Monday, tracking northward. There is ample QG lifting and possible coupling of a southeasterly low level jet north of the Pyrenees with the upper jet. It may not profit from the full amount of SREH but large hail and perhaps severe wind gusts (squall line) cannot be ruled out.

...SE Germany, N Austria, Czechia...

00Z soundings show 40 kts mid level winds and potential for good afternoon MLCAPE due to low level lapse rates. The mid level lapse rates seem to stay weaker which may limit the hail threat somewhat, but the convective mode should be discrete supercells given the lack of linear forcing factors and the presence of 15-20 m/s DLS and up to 200 m²/s² of SREH.

...Russia...

The stationary frontal zone bending east from Belarus is under the influence of moderate shear (some large hail chance) but storm motion parallel to the trigger may spoil the healthy environment for storms. GFS reflects this by weak lapse rates in the unstable region and higher to the south.