Storm Forecast
Valid: Sun 17 Apr 2016 06:00 to Mon 18 Apr 2016 06:00 UTC
Issued: Sun 17 Apr 2016 04:57
Forecaster: TASZAREK
A level 1 was issued for SW France and NE Spain mainly for severe wind gusts nad large hail.
A level 1 was issued for N Italy and SE France mainly for severe wind gusts, large hail and in lesser extent for tornadoes.
A level 1 was issued for W Belarus, E Lithuania and NE Poland mainly for severe wind gusts, large hail and tornado threat.
SYNOPSIS
A synoptic pattern dividing Europe into warm and moist air mass on SE and cooler and drier air over NW continue on Sunday. A jet streak similar as on Saturdays pattern, extends along thermal boundary from Iberian Peninsula, trough S France, Austria, Poland and Belarus. Within this area, a weak thermodynamic instability will develop thanks to the diurnal heating over N Iberian Peninsula, Pyrenees, S France, N Italy, Slovakia, SE Poland and Belarus. Along this line, a low CAPE/high shear thunderstorms capable of producing severe weather will be possible. A broad area with few hundredths J/kg of CAPE will develop in a warm section over E and SE Europe. However, due to a presence of a capping inversion and lack of large-scale forcing, probability for DMC in this area is rather low. Weakly sheared environment also limits threat for severe convective weather phenomena.
DISCUSSION
...N Italy...
A good overlap of steep lapse rates and rich boundary layer's moisture resulting in a CAPE up to 400-600 J/kg is located in the southern foot of the Alps. Due to a passage of a weakly pronounced short wave and a meso-low forming on the French/Italian border, this area will receive a sufficient large-scale lift to initiate convection. Developing updrafts in an environment of 15-20 m/s MLS, ~ 25 m/s DLS and nice veering vertical wind profile (3km SRH up to 300-400 m2/s2) will most likely transform into supercells. Although convection may remain low-topped, a severe wind gusts and large hail up to 3-4cm is possible to occur in such environment. Thanks to increased LLS (~ 8-12 m/s) along with SRH up to 1km, a tornado event in the late afternoon hours within isolated supercells cannot be ruled out. CI is expected to take place around 15 UTC. Thunderstorms should fade in the late evening hours when the thermodynamic instability will drop to 0.
...Pyrenees...
A passage of a weakly pronounced short-wave will help to initiate thunderstorms in the CAPE ~ 600-800 J/kg and DLS ~ 25 m/s around 12 UTC. Although the forecast hodographs seems to be not very favorable for supercells, given high DLS, a threat for rotating updrafts capable of producing large hail up to 2-3 cm and local severe wind gusts will exists in the afternoon hours. Severe weather threat should drop after 19-21 UTC when convective cells will no longer benefit from thermodynamic instability.
... SE Poland, W Belarus, E Lithuania...
Within a passage of a shortwave trough with well pronounced moist warm section(mixing ratios ~ 10 g/kg), a CAPE up to 1000-1200 J/kg (thanks to the diurnal heating) will develop in the afternoon hours. Convection should start on the SE part of Poland and towards NE continue to cluster. Due to persistent lifting signal, moderate CAPE and rich boundary layer's moisture, a multicell cluster in the late afternoon hours over Lithuania/Belarus border cannot be ruled out. Thanks to overlap of 25 m/s DLS with 1000 J/kg CAPE and 200-300 m2/s2 3km SRH, an supercells capable of producing large hail up to 3-4cm and severe wind gusts are also possible. It is worth to highlight that almost entire area where CI will take place will remain under an increased LLS up to 10 m/s and 1km SRH up to 150 m2/s2. Due to such favorable veering wind profile, a tornado threat will exist over entire lvl 1 area from 15 to 18 UTC. After 18 UTC, convection should transform into elevated, and thus the severe weather threat will drop.
