Storm Forecast
Valid: Tue 20 Jul 2010 06:00 to Wed 21 Jul 2010 06:00 UTC
Issued: Mon 19 Jul 2010 21:04
Forecaster: KOROSEC
A level 1 was issued for south-central England mainly for weak tornadoes.
A level 1 was issued for northern Ukraine, southern Belarus and northern Romania mainly for excessive convective rainfall, large hail and lesser extent for strong wind gusts.
SYNOPSIS
Weak geopetential heights are spreaded across much of Europe. Centered over western Black sea, a weak upper low serves as a focus for daytime driven activity over the Balkans. Another, more defined upper low slowly moves into western UK.
At surface, a cold front is placed NE-SW oriented across UK and another cold front remains rather slow SE-wards moving over the western Russia.
DISCUSSION
... south-central England ...
As the deep trough which now transformed into an upper cold-core low approaches British Isles during the day, a cold front slowly moves eastwards. Ahead of this front, warm and rather moist airmass advects towards central England. It seems that some hours of diurnal heating will be enough to yield a few hundreds J/kg of MLCAPE in the afternoon. Placed right under the jet-streak, around 20 m/s of deep-layer shear and around 10 m/s of LL shear will be available for organized convection. Backed LL flow should enhance SREH3 up to 100-150 m^2/s^2 and could support some rotating updrafts. Given these kinematics in place, a couple of low-topped supercells with threat for weak tornadoes cannot be ruled out.
... northern Ukraine, southern Belarus and northern Romania ...
A very strong instability in place due to high BL layer moisture and hot air over much of ESE Balkans towards the western Russia. A weakly capped environment will again allow widespread convective activity. The initiation is quite tricky to forecast over these areas, but given the numerous old outflow boundaries in place, storms are expected to form along them, as well as along the weak convergences zones around mountainous terrain. High MLCAPE of around 1500-2000 J/kg but weak shear and slow storm motion support threat mainly for excessive rainfalls/flash floods as well as some strong wind gusts and large hail. A level was placed where this threat is maximized. The similar activity will also be along the frontal convergence across western Russia, but again only briefly organized slow moving multicells/small clusters are expected given the weak shear.
... south-central Italy, western and Dinaric Alps ...
A 50% probability thunder line was placed mostly over the moutainous areas where convection is more likely. Recovering moisture and strong surface heating results in moderate instability within the environment of only minor or zero shear (DL shear of around 5 m/s only). Pulse storms could be expected along the convergences across Apeninnes and Dynaric alps. The main threat seems to be locally intense rainfalls and some strong wind gusts. Activity will quickly diminish towards the sunset.
... NE Spain, Pyrenees and SW France ...
With a weak low pressure area over Spain, some backed flow will be advecting moisture into NE Spain and SW France. A more favorable kinematic environment seem to be enough for better organized storms especially across the Pyrenees mountains during the day. MLCAPE of around 1000 J/kg and environment with 10-15 m/s of deep layer shear should support multicells or a small cluster of storms there. Given the low coverage, a threat level 1 was not issued at the moment, but more organized storms may pose a risk for some isolated large hail and strong wind gusts. Towards the Wednesday morning, some elevated convection is possible in SW France ahead of the approaching front.
