Storm Forecast
Valid: Tue 27 Aug 2019 06:00 to Wed 28 Aug 2019 06:00 UTC
Issued: Mon 26 Aug 2019 21:53
Forecaster: DAFIS
A level 2 was issued for E Spain for large or very large hail, severe wind gusts, excessive precipitation, and tornadoes.
A level 1 was issued for E Spain and N Algeria for large or very large hail, severe wind gusts, and excessive precipitation.
A level 1 was issued for UK for excessive precipitation, large hail, severe wind gusts, and tornadoes.
A level 1 was issued for Denmark, E Germany, W Poland, Slovakia and parts of Czech Republic and Hungary mainly for severe wind gusts and excessive precipitation.
Two level-1 were issued for S Germany, Austria, Croatia, Bosnia, and Herzegovina and Montenegro mainly for excessive convective precipitation.
A level 1 was issued for parts of Russia mainly for severe convective wind gusts.
SYNOPSIS
Two major troughs affect the weather in Europe. One dissipating trough over Central Europe with an axis from Germany towards Italy provides lift to unstable air masses in Central and East Europe, while a long-wave trough over Spain creates favorable conditions for severe storms. An embedded short-wave trough will cross the UK on Tue 27/08, creating a jet-streak. Near the surface, the frontal activity is weak or absent, except a fast-moving cold front in W Russia.
Very warm air masses have reached the North Sea and W Scandinavia (almost 8-9 degrees above the 1979-2010 avg at 850 hPa) due to the interaction between the low-pressure systems in Western Europe and the high-pressure system in Eastern Europe with a center over the Baltic States on Tue 27/08.
DISCUSSION
... Spain and Algeria ....
Strong PVA associated with the trough which is crossing the Iberia Peninsula results in a large-scale lift of very unstable air masses. With 10-15 g/kg PBL mixing ratios and steep mid-level lapse rates, NWP models produce excessive MLCAPE values, locally exceeding 3.000 J/kg. Even at the areas with lower CAPE, the overlap of strong instability and 15-20 m/s DLS suggest that storms will be able to organize in clusters and some of them will become supercells producing all kinds of severe weather, especially in the Balearic Islands. Large or very large hail will be the main threat, but also excessive precipitation (also small hail in large quantities, apart from rainfall). Low LCLs and veering low-level winds increase the probability of tornadoes.
In the mainland of Spain storm activity should stop in the late afternoon and big clusters of storms will continue propagating east until the early morning of Wed 28/08.
Algeria is also a candidate to receive large hail in the early afternoon, mainly on the Atlas mountain range.
.... United Kingdom ....
As the short-wave trough from the west will cross the country, the confluent flow over land where mixing ratios are calculated to exceed locally the 10 g/kg and 6-7 K/km mid-level lapse rates will result in some hundreds of CAPE. DLS in the order of 15-20 m/s in the afternoon, will be reduced to 10-15 m/s in the early night, with 0-3km bulk shear of the same order. One or two supercells may form in the late afternoon able to produce large hail, severe wind gusts, and tornadoes. Veering wind profiles and low LCLs with 0-1km bulk shear close to 10 m/s increase the probability of tornadogenesis.
.... Denmark, E Germany, W Poland, Slovakia and parts of Czech Republic and Hungary ....
Warm and moist air-masses under a weak wind flow will feed diurnally driven storms. A level-1 area has been issued for the areas with the least convective inhibition where weak storm motions and high PWAT can lead to flash floods. Moreover, in W Poland the much drier PBL may lead to some microbursts in the afternoon.
.... S Germany, Austria, Croatia, Bosnia, and Herzegovina and Montenegro ....
A pool of warm and moist air masses can be found in this part of the Balkans, where we expect diurnally driven storms and a few elevated storms during the night of Tuesday. Slow storm motions increase the threat of flash floods.
.... Russia ....
As a cyclone is moving east NW of Moscow, a cold and dry air intrusion is forecast. The strong mid-level flow can easily be translated to the surface during the storms that are expected before 12z, producing locally severe convective wind gusts.
