Storm Forecast
Valid: Mon 11 Jul 2016 06:00 to Tue 12 Jul 2016 06:00 UTC
Issued: Mon 11 Jul 2016 04:41
Forecaster: VAN DER VELDE
A level 2 was issued for E France, N Switzerland, S Germany, N Austria, Czech Republic and Poland mainly for large hail and severe convective wind gusts.
A level 1 was issued for NE Spain mainly for large hail.
A level 1 was issued for Belarus, Lithuania and Latvia mainly for chances of tornadoes.
SYNOPSIS
A low pressure system near the Shetland Islands produces a trough with tight pressure gradient in the mid levels over western Europe through the Baltic region, causing strong mid/upper level winds. A weak surface cold front under this gradient from Spain to Lithuania is the trigger for deep convection, however the absence of marked convergence zones in low levels and weak forcing from the trough suggest a broad region with isolated to scattered storm initiation.
DISCUSSION
...France to Poland...
Some 12 g/kg mean mixing ratio over the lowest 1000 m should be present according to GFS between S France and Latvia. Moderate lapse rates overlap from E France to Czech Republic, and strong lapse rates are present over Spain and the region between Austria and Belarus. Weakly capped MLCAPE of 1500 J/kg is forecast by GFS from SE Germany to NE Poland. In the presence of 17-22 m/s 0-6 km shear, hodograph curvature and not too strong forcing, discrete supercells and some clusters of multicells are the likely storm mode along the warm side of the cold front, mainly from E France into central Europe. LCL heights are forecast lowest by GFS over France into Germany, and a moderate 1500-2000m over Poland, which aids broad updrafts and chances of large or very large hail. Severe downdraft winds can cause damage. Microburst potential is indicated by delta-theta-e (buoyancy generated by evaporational cooling) over 20K centered over/around Czech Republic. Slightly enhanced 0-1 km shear could be present over E France with somewhat elevated tornadogenesis chances as result.
...Belarus, Lithuania, Latvia...
Although MLCAPE is a lot weaker (<400 J/kg) along the warm front passing over this region, SREH and 0-1 km shear are enhanced to 250 mē/sē and 7-12 m/s respectively, increasing the odds of tornado production by storms in the low LCL environment. Precipitable water is much greater also in the Baltic region and N Belarus than in central Europe, with chances of excessive local rainfall but storm motion vectors should mostly keep this from happening.
...Spain...
In the hot dry air with LCL above 2500m, weak MLCAPE is indicated by GFS. Storms will probably struggle to develop due to entrainment, even when capping is rather weak in the afternoon. Helped by orography this may be most likely over E/C Spain, and wind shear is enough to turn storms into supercells, which then may produce an isolated large hail or severe wind gust event.
