Storm Forecast
Valid: Sat 04 Jul 2015 06:00 to Sun 05 Jul 2015 06:00 UTC
Issued: Fri 03 Jul 2015 21:40
Forecaster: DAFIS
A level 1 was issued for parts of S Denmark, NW Germany, Netherlands, Belgium, Luxembourg and NE France for excessive rain, large hail and to a lesser extent weak tornadoes.
A level 1 was issued for the Alps for excessive rain, large hail and to a lesser extent severe wind gusts .
SYNOPSIS
A ridge is stretching from West Mediterranean towards South Scandinavia. A cold pool is placed over East Balkans and West Black Sea with rather high positive vorticity values and another low pressure system swirls NW of the United Kingdom and Ireland. A warm front is placed over North Germany in the morning, moving north, followed by a cold front later during the day and a occluded front during the second half of the day would be responsible for severe weather events in West Europe. Only level 1 is issued due to large differences and uncertainties between the NWP models.
DISCUSSION
....West Europe....
Storms in the East UK will continue to move NE during the morning and eventually will dissipate till noon. A very moist (mixing ratios ~12g/kg) and warm boundary layer stretches from NE France to NW Germany and along with diurnal heat, contribute to produce large values of MLCAPE around 2500 - 3000J/kg according to GFS and ECMWF latest runs (CAPE is lower in central France but DLS has a maximum value of 20m/s in the afternoon). During the late evening, southeasterly weak flow at 850hPa and a stronger southwesterly flow at higher levels (~20m/s) lead to a curved hodograph with almost 400mē/sē (GFS) or 300mē/sē (ECMWF) of SRH but in a limited area, so we stay with level 1. Moreover DLS of ~20m/s in NE France after 18z and 0-3km wind shear of 20m/s may lead to one or two well organized storm cells or supercells with large hail being the main threat, especially at Hainaut - Namur provinces of Belgium and Luxembourg. Also tornadoes are not ruled out but the probability is low due to high LCLs, above 1000m and there are big differences between GFS and ECMWF runs regarding to LLS. Elevated storms during the night should move NE to Germany and South Denmark with less risk of severe events.
During the early morning of Sunday, the SW parts of France (Poitiers - Bordeaux provinces) may face a severe threat due to very high values of DLS and SHER but uncertainties remain due to early morning stable conditions.
....Alpine region....
A very hot and dry boundary layer exists at the Alpine region and models forecast CAPE values that exceed 3000J/kg. DLS around 10m/s may support the development of some strong cells with isolated large hail and severe downbursts due to dry environment and high LCLs.
....East Balkans....
A mid/upper level low swirls in the area with some notably amounts of positive vorticity and high resolution NWP models forecast a large area of convective phenomena but with low risk of severe events due to lack of wind shear and low CAPE values that indicate pulsating storms.
