Valid: Tue 07 Aug 2018 06:00 to Wed 08 Aug 2018 06:00 UTC
Issued: Mon 06 Aug 2018 19:54
A level 2 was issued for France, Belgium, the Netherlands and NW Germany mainly for severe wind gusts, large hail and tornadoes.
A level 2 was issued for N Spain mainly for large hail and severe wind gusts.
A broad level 1 area was issued for parts of Spain, France, Switzerland, Austria, Luxembourg, N Italy, Germany, the Netherlands, Belgium, and Denmark mainly for excessive precipitation, large hail, severe wind gusts, and tornadoes.
A level 1 was issued for W Russia mainly for large hail and severe wind gusts.
Several troughs are developing over Europe, especially to the western parts where the most interesting features can be found, destroying the strong ridge that brought new high-temperature records. On Tuesday, two main troughs will create favorable conditions for severe weather, one in W Europe denoted by 2 level-2 areas and a broad level 1, and another one in NE parts of the continent where less moisture and dynamics are forecast.
.... France, Belgium, the Netherlands and NW Germany ....
An approaching trough from the Atlantic with strong vorticity advection over a wide area with unstable air masses will lead to severe weather phenomena. First, France will be affected by storms that will be able to cluster in MCSs and supercells producing all kinds of severe weather. At the right exit of the mid-level jet streak the lapse rates may reach 8 K/km creating an overlap of 2-3 kJ/kg CAPE with 20-25 m/s DLS. In the afternoon and night as the storms will propagate NE towards Benelux, increasing low/mid-level shear creates some hundreds of SREH and storms can gain strong rotation, producing severe tornadic supercells. These storms will be able to produce large hail, severe wind gusts and tornadoes.
The level-1 area that surrounds the level-2 areas shows the locations of the storms where they may become severe. Locally large hail, severe wind gusts, excessive precipitation from slowly moving storms and landspouts / tornadoes are well possible especially during the late afternoon - night. Thunderstorm activity will continue overnight till the morning of Wednesday but with a limited threat for severe phenomena.
.... N Spain ....
Moist low-level air masses overlap with very steep lapse rates in N Spain. The strong cap will make it difficult for air parcels to reach their LFC driven only by diurnal heating, but local convergence zones (mostly near mountains) will provide the necessary lift to produce thunderstorms. NWP models forecast about 2-2.5 kJ/kg CAPE and locally enhanced DLS (15-20 m/s). Storms will be able to produce large hail and severe wind gusts.
.... W Russia ...
A short-wave trough brings cold mid-level air masses and increases the mid-level wind speeds, creating some 15-20 m/s DLS patches in NWP output which overlap with 800 - 1500 J/kg CAPE. Given the fact that dry air will penetrate the mid-levels large hail and severe wind gusts can be a serious threat. Moreover, 1-2 landspouts cannot be ruled out as LCLs will be very low and LLS in the order of 10 m/s.