Valid: Sun 03 Aug 2014 06:00 to Mon 04 Aug 2014 06:00 UTC
Issued: Sun 03 Aug 2014 07:34
Forecaster: VAN DER VELDE
A level 2 was issued for E Germany, W Poland, E Denmark, S Sweden and SE Norway mainly for excessive convective precipitation, large hail and severe wind gusts.
A level 1 was issued for SE Germany, N Italy, Austria, Czechia, W Slovakia and W Hungary mainly for excessive convective precipitation.
A level 1 was issued for N Spain, S France, Italy, W Balkan mainly for large hail.
A level 1 was issued for NE Ireland and NW UK mainly for tornadoes.
A low pressure area is centered over Scotland. Its cold front has advanced into France and western Germany while a warm sector with high MLCAPE values of 1500-2500 J/kg is bounded by drier air to the east of central Poland to Romania, with very steep lapse rates and high LCLs. This warm sector and its CAPE is funneled into a occlusion front converging over NE Germany, Denmark and S Norway. Over central Europe slow storm motion and weak shear and upslope winds toward the Alps contribute to efficient precipitation producing storms.
Upper shortwave troughs cause ascending motion over SW France and W Balkan during afternoon and evening, Italy during the morning and early afternoon, and central France to Belgium during the night.
...E Germany, W Poland...
Strong CAPE due to very steep lapse rates from surface to 600 hPa resides in this region. The decent deep layer shear (10 m/s 0-6 km) ensures healthy multicell systems developing in a convergence region near the German/Polish border. 1500-2000 m LCLs aid in the updraft strength. Large and very large hail can result.
As written for upstream areas, high CAPE - moderate shear environment also is in place over this region, with large hail threats, but may additionally consist of advected mesoscale convective systems posing a more significant precipitation and severe wind gust threats. WRF models produce strong signals for nocturnal MCSes even moving deep into southern Norway. Additionally, supercells are also likely given 15 m/s deep layer shear and some 200 mē/sē 0-3 km SREH. Over western Sweden also 0-1 km shear will be elevated over 10 m/s which can help tornadogenesis.
...N Spain, S France, Italy...
15 m/s deep layer shear should help organize rotating updrafts which can grow large hail, however, lapse rates have decreased to mediocre values, leaving low buoyancy, particularly in the higher levels (mixed phase region). This and the low LCLs in most places are counterproductive to hail. It may be best in northern Italy during the morning and early afternoon, while waterspouts are also possible.
A region within the low rounded by the occlusion front seems to have a mix of CAPE, slow storm motion, weak shear and high vertical vorticity which can locally be spun up in a spout-type tornado or two.