Storm Forecast
Valid: Sun 14 Jun 2009 06:00 to Mon 15 Jun 2009 06:00 UTC
Issued: Sat 13 Jun 2009 23:53
Forecaster: SCHLENCZEK
A level 1 was issued for SE Finland and NW Russia mainly for tornadoes, large hail and severe gusts.
A level 1 was issued for NE-central France, S Belgium / Luxembourg and W Germany mainly for large hail and severe gusts.
SYNOPSIS
On Sunday, a strong southwesterly flow will establish over SW-central Europe between an upper ridge over the central Mediterranean and a trough near the British Isles. According to GFS and WRF, very warm and moist air should be advected into east-central France and western Germany during the period which will lead to moderate instability.
Another low pressure system, initially located over the N Baltic Sea, will lead to unsettled conditions over parts of Finland, the Baltic States and W Russia. Ahead of its cold front, very warm air is advected northward towards extreme SE Finland. As the occlusion process continues, the potential of severe convective weather will gradually decrease.
A small upper jet streak stretches from SE Spain towards NW Italy. Some instability is in place and thunderstorms may develop.
DISCUSSION
...NE France, S Belgium, Luxembourg, SW and W Germany...
Diurnal heating as well as LL moisture advection will lead to MLCAPEs around 1,5 kJ/kg over eastern France and southwestern Germany on Sunday afternoon. At upper levels, a strong SWerly flow is present and leads to 15 - 25 m/s deep layer shear in the entire LVL1 region. It is still uncertain if a surface low will develop over W Germany (which is shown by WRF 12Z ). If so, LL winds will back especially over large portions of Rheinland-Pfalz and this will significantly enhance directional shear and SRH in that particular region. Even without the development of a SFC low in W Germany, SRH3 will reach values around 150 mē / sē which is sufficient for rotating updrafts. A capping inversion should preclude widespread initiation at first but the cap is forecast to weaken in the evening hours. First storms will probably become supercellular, posing a threat of large hail and damaging gusts as there are quite high values of DCAPE. Later on, isolated storms may merge into one or two large MCSes with heavy rainfall and severe gusts being the main threat. Especially extreme E France and W Germany have to be monitored as an update may become necessary.
The severe threat may continue into central and eastern Germany during the night hours but this scenario is rather uncertain. This may also be included in a possible update.
...SE Finland and NW Russia...
In an environment with 10 - 15 m/s deep layer shear, CAPE in order of 1 - 2 kJ/kg is present. Some forcing along the frontal boundary and near local convergence zones should be sufficient for convective initiation. Most storms will be organized multicells and there may be also a few supercells, capable of producing large hail and severe gusts. Especially in the eastern part of the LVL1 area, tornadoes may be possible as strong LLS is in place and the LFC heights will stay rather low.
