Storm Forecast
Valid: Sat 15 Aug 2015 06:00 to Sun 16 Aug 2015 06:00 UTC
Issued: Fri 14 Aug 2015 21:24
Forecaster: DAFIS
A level 2 was issued for East Spain and the Balearides Islands mainly for excessive rain, large hail, severe wind gusts and tornadoes.
A level 1 surrounds the level 2 area for the same threats but with less coverage.
A level 1 was issued for parts of Denmark, Germany, Czech Republic and Poland mainly for excessive rain and large hail.
A level 1 was issued for the Alpine region of North Italy, SE Austria, Slovenia and North Croatia - West Hungary mainly for excessive rain, large hail and severe wind gusts.
A level 1 was issued for East Ukraine mainly for excessive rain, large hail and severe wind gusts.
SYNOPSIS
A complex pattern takes place in Europe, with many fronts at the most parts of the continent. A longwave trough extends from Iceland to the West Mediterranean Sea with a jet streak placed in South Spain - NW Africa. Scandinavia is under ridge conditions, a shortwave trough is over Ukraine and the upper low in the SE Mediterranean that caused very unusual weather conditions (for this time of the year) in Italy and Greece, vanishes during Saturday.
At the surface, two low pressure systems swirl over Iceland and Germany, whilst another one in NW Russia results in strong vorticity advection which creates deep layer shear but convection is very limited due to weak lapse rates. Such pattern will remain mostly quasi-stationary during the forecast period without any major changes in the position of the main frontal zones.
DISCUSSION
.... East Spain and the Balearides Islands ....
Steep low and mid-level lapse rates atop moist boundary layer are expected to contribute to the development of moderate to high CAPE values over this area. Southeasterly low level flow due to sea breeze, should advect quite moist airmass from the Balearic Sea into East Spain, with rather low LCLs likely. With westerly jet-streak at 500 hPa overlying the region, we do not expect much curvy hodographs, but deep layer wind shear (DLS) might actually well exceed 25 m/s.
As SREH is simulated to be locally over 300 m²/s², isolated supercells capable of large hail, damaging wind gusts and tornadoes (waterspouts) are possible. LLS about 10m/s should also support the development of LL rotation of the storms, so that waterspouts might form before 0900 UTC. In North Africa, strong DLS may help any storms to become severe but CI may be limited due to sporadic CAPE signals until the afternoon hours. Later on, WRF produces a line of storms at the convergence zone near the coast under strongly shear environment, so DMC is expected.
.... Denmark, Germany, Czech Republic and Poland ....
At 06Z, a strongly tilted cold front will be situated over Germany with a slow down of its NEward shift. North parts of Germany and South parts of Denmark should be affected by DMC early in the morning with 0-3km wind layer shear exceeding 15m/s. Later in the day, as the front moves N-NEwards, dew points of about 20°C in NE Germany and Poland, with MLCAPE values of more than 2000J/kg locally, will feed the development of one or two MCSs with excessive rain (PW > 40mm) and large hail being the main threats. Isolated storms over the North Czech Republic could produce excessive rain as the DLS is predicted below 15m/s and the cells will be stationary.
.... Alps and eastern parts ....
In these areas, moderate to high CAPE values and DLS are juxtaposed but local convergence zones within the moist BL, may result in storms able to produce excessive rain and locally large hail. The highest severe risk probably exists in SW slopes of the Alps (Piemonte), Trentino and after 18z at the areas extending from NE Croatia to SE Austria where low and high resolution models predict a zone of CI under moderate LLS and SREH over 250 m²/s².
.... East Ukraine ....
Steep lapse rates and low level moisture advected by the Black Sea result in MLCAPE of 2 to 2.5 kJ/kg locally among the upper air low. DLS may exceed 15m/s, so DMC is forecast for this area, where excessive rain and large hail is expected. We may also receive severe wind gusts reports as mid - level dry air prevails (Tuapse sounding) and LCLs seem to be rather high according to GFS.
