Storm Forecast
Valid: Wed 08 Aug 2018 06:00 to Thu 09 Aug 2018 06:00 UTC
Issued: Tue 07 Aug 2018 20:32
Forecaster: PUCIK
A level 2 was issued across N Spain mainly for large to very large hail and damaging wind gusts.
A level 1 was issued across E Spain mainly for large to very large hail and severe wind gusts.
A level 2 was issued across S France mainly for large hail, excessive rainfall and severe wind gusts.
A level 1 was issued across S France, Italy, the Alpine range, Germany, W Czech Republic and W Poland mainly for large hail, excessive precipitation and severe wind gusts.
A level 1 was issued across Central Sweden mainly for severe wind gusts.
A level 1 was issued across NE Turkey, Caucasus region mainly for large hail and excessive precipitation.
SYNOPSIS
In between of a deep trough situated over the Atlantic and an extensive ridge over Central-East Europe, a widespread area experiences a WAA advection regime. A plume of enhanced lower tropospheric moisture will have reached N Scandinavia by the end of forecast period. A pronounced short-wae trough will begin affecting W Iberia by 18 UTC and will cross Bay of Biscay and parts of extreme W France by 06 UTC Thursday. A cold front will accompany the passage of the short-wave. Earlier, a weakening cold front is forecast to cross Denmark and Germany. An isolated to widespread thunderstorm activity is forecast in a large belt from Spain through France, Germany to N Scandinavia.
DISCUSSION
... Spain ...
Combination of steep lapse rates and abundant lower tropospheric moisture will result in CAPE values locally exceeding 2000 J/kg, particularly over Ebro valley, where thermal low over Central Spain induces easterly flow advecting moisture from the Mediterranean. In the afternoon hours, moderate to strong vertical wind shear is forecast, ranging from 10 to 20 m/s increasing from south to north. In such setup, strong multi to supercells are forecast with threats of large to very large hail and severe wind gusts.
Towards the late evening and night hours, over N Spain, an increase in both DLS and SRH is forecast, as well as of convective coverage as the short-wave trough approaches. Here, in environment very conducive for long-lived supercells, the overall threat will be higher compared to the rest of Spain and thus a Lvl 2 is warranted.
... France ...
A rather complex forecast scenario will unfold over the region with scattered afternoon storms erupting over Massif Central and the Alps. These will be organized into multicells in weak to moderate vertical wind shear with threats of isolated downbursts, large hail or local flooding.
Towards the morning hours, in conjuction with the approach of the short-wave and the front, widespread initiation is simulated by models over Bay of Biscay and SW France. In strongly sheared environment, these storms will likely first form on the cool side of boundary, in the elevated form, posing risks of large hail and excessive rainfall. As storms move east and cluster into a large MCS, there will be a chance for storms to become surface-based with a threat of severe wind gusts. Lvl 2 highlights an area with the highest combined threat posed by the late night and morning activity.
... Italy ...
Mostly disorganized storms in weak vertical wind shear will pose threats of isolated large hail, downburst or a flash flood risk in the environment of abundant CAPE.
... Germany, W Czech Republic, W Poland ...
Considerable uncertainty regarding both the lower tropospheric moisture and the convective coverage can be found in the models. A convergence zone, connected to the weakening cold front, will serve as an initiation point. Vertical wind shear is forecast to increase in the afternoon hours, with DLS values ranging from 10 to 15 m/s. Some well organised multicells may be capable of large hail, severe wind gusts (deep boundary layer suggests strong evaporational cooling potential) and excessive precipitation.
... Sweden ...
A lvl 1 is issued for the region, where model output hints on a development of a convective line in environment of strong vertical wind shear.
