Storm Forecast
Valid: Mon 12 Sep 2016 06:00 to Tue 13 Sep 2016 06:00 UTC
Issued: Mon 12 Sep 2016 03:57
Forecaster: VAN DER VELDE
A level 1 was issued for NE Iberian Peninsula and S France mainly for large hail.
A level 1 was issued for N Morocco and N Algeria mainly for large hail and severe wind gusts.
A level 1 was issued for NW Iberian Peninsula mainly for excessive convective rain and tornado chances.
A level 1 was issued for Turkey mainly for excessive convective rain and large hail.
A level 1 was issued for SE France mainly for excessive convective rain.
A level 1 was issued for SE Italy region mainly for excessive convective rain and waterpout type tornadoes.
SYNOPSIS
A large mid level anticyclone over central Europe is making way for a long wave Atlantic trough. Steep mid level lapse rates are present over much of the European mainland, and low level moisture creates a few hundred J/kg MLCAPE between the Mediterranean and the line Denmark - Romania. However, lifting mechanisms are weak and subsidence affects the area, suppressing convection. The region of S Italy to Turkey is affected by two troughs generating storm activity. A slight trough is found in PV fields moving northward over Spain. GFS shows cyclogenesis at night over the Bay of Biscay with convective activity. In general, various WRF and large scale models struggle producing much precip signals across Spain, most of France and Germany while GFS shows weakly capped parcel layers. In case of Spain quite strongly so.
DISCUSSION
...NE Iberian Peninsula...
Isolated initiation is likely in the Ebro Valley region where moist air and steep lapse rates generate 1500 J/kg MLCAPE. With moderate vertical shear (>10 m/s) and LCL around 2000 m strong and rotating updrafts are likely to produce large hail and local severe wind gusts (20 K delta theta-e). A slight trough should help inititation. Storms may perhaps stay alive and shift to N Spain. At night GFS allows development of a MCS over Bay of Biscay, but this scenario is not found in other models except a French NMM.
...NW Iberian Peninsula...
The occluded front allows convection moving parallel to the front which can lead to training cells leaving excessive rain. Over land, 0-1 km shear is enhanced over 10 m/s and SREH over 200-300 mē/sē, allowing mesocyclones with tornado chance.
...N Africa...
High-based convection should get going in response to lift from an upper low moving eastward. The shear seems to be higher where the cap is stronger, but chances are good that strong storms develop with chances of severe wind gusts/dust storms, and large hail.
...Turkey...
Moderate shear, 2000m LCL, an incoming trough and some CAPE combine into a large chance of storms, with a slight threat of large hail and heavy precipitation.
...SE France...
Models consistenty produce convection, from upslope flow of moist Mediterranean air, and with weak storm motion these can produce excessive convective rainfall.
...SE Italy, Thyrrenian and Ionean seas, SW Balkan...
Waterspouts are quite likely under the low, although GFS 0-2 km CAPE does not look that strong. Slow storm motion is in support and can also create localized flash floods from convective rainfall.
