Storm Forecast
Valid: Tue 10 Aug 2010 06:00 to Wed 11 Aug 2010 06:00 UTC
Issued: Mon 09 Aug 2010 20:18
Forecaster: KOROSEC
A level 2 was issued for the eastern Belarus and extreme NW Russia mainly for large hail, damaging wind gusts, excessive convective rainfall and lesser extent for tornadoes.
A level 1 surrounding the level 2 was issued for the west-central Ukraine, the rest of Belarus and extreme northwestern Russia mainly for large hail, damaging winds, excessive convective rainfall and lesser extent for tornadoes.
A level 1 was issued for Netherlands, northern Belgium, Denmark, extreme SW Sweden and southern Norway mainly for excessive convective rainfall, strong wind gusts and lesser extent for tornadoes.
A level 1 was issued for eastern Spain mainly for large hail and damaging wind gusts.
A level 1 was issued for northern UK mainly for funnel clouds/spout-type tornadoes.
SYNOPSIS
A large long-wave trough over north-central Europe slightly weakens while staying stationary during the forecast period. From the NE Atlantic sea, a rather intense upper low moves into northern UK. Its frontal system affects NW Europe and moves towards southern Scandinavia. Elswehere, several near-surface frontal/convergence zones are placed where severe convective activity is expected.
DISCUSSION
... Belarus, Ukraine and extreme NW Russia ...
Yet another day of active severe storms is expected over these areas. The quasi-stationary surface front will be the focus for numerous storms with widespread activity. Ahead of the NE-wards moving short-wave trough a large-scale ascent will support widespread initiation. High instability with MLCAPE-a 1000-1500 J/kg is expected, well overlaping with moderate deep-layer shear of 15-20 m/s across the level 2 area. This environment seems favorable for another round of well organized multicells, as well as a few supercells where storms will be able to stay more isolated. Large hail (locally very large hail possible), damaging winds and excessive convective rainfall are the primary threat. Given the around 15 m/s of 0-3km shear, but very low LL shear, tornado threat seems to be quite limited against the previous days. Clustered storms will bring a local flash flood threat.
... Netherlands, northern Belgium, Denmark, extreme SW Sweden and southern Norway ...
A frontal system associated with a PVA maximum/deep upper low moves across the North sea in the afternoon. Convective activity is expected mostly along or just ahead of the surface cold front, where several hundreds J/kg of MLCAPE will be available. In rather highly sheared environment, a couple of low topped supercells will be possible, bringing the threat for strong wind gusts. Near 10 m/s of low-level (mostly) unidirectional shear and very low SREH limits the tornado threat, but a tornado or two cannot be completely ruled out given the amount of LL shear and locally enhanced helicity.
In the evening hours, storms will likely cluster into one or two larger systems/MCS and move across Denmark and into SW Scandinavia overnight on Wednesday. With still marginal instability available and at least 20 m/s of deep-layer shear, a well organized MCS with bowing segments is possible. For this reason, a level 1 was also extented towards the southern Norway and extreme SW Sweden.
... eastern Spain ...
Beneath the nose of the upper ridge, marginal to moderate instability seems to build up during the day over eastern half of Spain. Strong surface heating should overcome/erode the cap in the mid afternoon hours and isolated storms should initiate, mostly aligned to local topography. An organized severe convection can be expected given the around 10-15 m/s of deep layer shear which should pose a threat for large hail and strong/severe wind gusts with the strongest cells. A level 1 was issued to cover the marginal threat as widespread activity is not expected.
... northern UK ...
Placed under the upper low, moderate LL CAPE/lapse rates seems to build up during the day. With very weak wind field in place and LCLs around 1000m ASL, numerous funnel cloud or spout-type tornadoes (waterspouts) can be expected.
