Storm Forecast
Valid: Wed 17 Aug 2011 06:00 to Thu 18 Aug 2011 06:00 UTC
Issued: Tue 16 Aug 2011 19:40
Forecaster: KOROSEC
A level 1 was issued for S Finland, extreme NE Europe and W Russia mainly for large hail, strong winds and excessive convective rainfall.
A level 1 was issued for central France mainly for isolated large hail and strong wind gusts.
SYNOPSIS
A ridging omega-block pattern dominates south-central Europe with a zonal flow established to its north. A large upper vortex remains centered over NE Atlantic sea. Similar as during the previous days, a short-wave trough rounds across the Baltic states with a SFC front extending southwards across extreme eastern Europe. Yet another short-wave trough crosses S Sweden. A weak upper low affects extreme S Balkans. Elsewhere, hot summer conditions prevails.
DISCUSSION
... S Finland, extreme NE Europe and W Russia ...
A potent short wave trough across the Baltics continues trailing further NE and serves as a focus for yet another active convective day along/ahead of the SFC front. This surface front moves into western Russia by Thursday morning. Moderate mid-level jet rounds its base, providing around 10-15 m/s of deep layer shear. With very humid and hot BL airmass, moderately strong instability is in place and conditions are again favorable for explosive convection once the weak capping will be eroded by midday. Quite some QG forcing will be in place, so rather widespread activity will take place, initiated mainly along the old pre-existing outflow boundaries and local topography features. Storms will gain organization into multicells as well as a few supercells. Those could pose a threat for large hail, damaging winds and intense rainfall/flash flood events. A few larger clusters are likely to form later in the afternoon/evening hours. A tornado threat is unlikely given the non-existent LL shear, though a spout type funnel/tornado cannot be completely ruled out given the quite high LL CAPE/lapse rates and weak LL wind field in place, especially around the Baltic States and gulf of Finland.
... central France ...
On the western flank of the strong ridge across the Mediterranean, a plume of strong EML advects across Spain into south-central France. At surface, a warm front advects northwards across France. Meanwhile, a moisture recovery is expected from the western Mediterranean into France as SFC cyclogenesis takes place over western France during the day. GFS again overestimates the SFC dewpoints against the other models, but its likely that around 1000 J/kg is reasonably expected across the area. Right jet entrance region provides some upper level divergence and some forcing will become available. Despite quite strong capping inversion, it seems that a few isolated storms will probably form. Given the moderate 15-20 m/s deep-layer shear and around 100-200 m^2/s^2 of SREH3, overlaping with moderate instability, well organized storms could form. Capable of producing large hail and locally some strong to severe winds gusts given the high LCL heights and dry mid-levels. Further south into extreme N Spain a possibility for an isolated severe storm or two exists, even the capping seems quite strong there. But seem quite uncertain to warrant an extension of a level 1 so far south attm. Later towards the evening/overnight, some elevated convective activity is possible further north along the advecting warm front as LLJ jet slightly intensifies.
... Greece and surrounding areas ...
A weak upper low rotates over the extreme southern Balkans today, resulting in mainly daytime driven convective activity. Moderate instability overlaps with only marginal shear, so well organized DMC is unlikely. Storms are again expected to form along the local complex topography and daytime driven convergence zones moving inland from the surrounding seas. However, locally some intense rainfall/flash floods threat, strong wind and hail is possible, but too isolated activity to warrant a categorical threat level 1.
... southern Sweden ...
Another weak short-wave trough crosses this area on Wednesday where cold mid-levels results in a few hundreds J/kg of MLCAPE, but in almost non-sheared environment. So mainly daytime driven weakly organized storms are expected to take place, diminishing after sunset when instability vanishes. A few small hail events cannot be ruled out, as well as a waterspouts or a funnel cloud given the low-topped cells and favorable LL lapse rates. Though remaining sub-severe, so no threat level is needed attm.
