Storm Forecast
Valid: Tue 09 Aug 2016 06:00 to Wed 10 Aug 2016 06:00 UTC
Issued: Mon 08 Aug 2016 22:03
Forecaster: DAFIS
A level 1 was issued for parts of W Russia, Belarus and SE Poland mainly for severe wind gusts, large hail and tornadoes.
A level 1 was issued for the N Italy, S Austria and Slovenia mainly for large hail,severe wind gusts and to a lesser extend excessive precipitation.
A level 1 was issued for Spain mainly for large hail and severe wind gusts.
A level 1 was issued for S Balkans mainly for excessive precipitation and to a lesser extent large hail.
SYNOPSIS
The main feature during this outlook is the positive tilted, amplifying longwave trough that its axis extends from Scandinavia towards Iberian Peninsula and is slowly moving towards the east. The mid-level low pressure system over the Balkans will perish until Wednesday morning, but steep lapse rates persist over the unstable air masses. On the surface a vigorous low pressure system with sharp pressure gradients moves through Scandinavia with its cold front extending from NW Russia all the way south to Italy.
DISCUSSION
.... W Russia, Belarus and SE Poland ....
As the frontal boundary near the surface moves E-SE during Tuesday, in the warm sector moist air masses create some hundreds of CAPE, up to 1500 J/kg according to GFS. Indications of moderate DLS (15-18 m/s) but very localized SREH suggest that an isolated supercell may form with a primary chance of large hail. Along the convergence zone, a linear convective system may form later in the afternoon, taking into account the 0-3 km flow that aligns almost parallel to the baroclinic zone. There, 0-1 km shear and SREH0-1km seem enhanced after 15z especially in NE Belarus and Russia where models suggest a favorable environment for rotating updrafts in the most discrete cells with chances for large hail, severe wind gusts and tornadoes.
.... N Italy, S Austria and Slovenia ....
As the cold front meets the steep terrain of the Alps, it stalls and the complex wind field near the surface may result in numerous of convergence zones, where warm and moist air masses pre-exist. NWP models predict meager CAPE values, higher in NW Italy, but moderate to strong DLS and SREH increase the chances of large hail. Furthermore, there are strong signals in GFS model for excessive precipitation in N Italy as PW reaches 40mm.
.... Spain ....
As the amplifying trough crosses the Iberian Peninsula, it shifts east and enters the West Mediterranean during the end of the forecast. Tds near 18°C suggest a moist PBL in NE Spain and NWP models forecast marginal CAPE of 400-600 J/kg with a weak cap, but CAPE increases during the late afternoon hours North of Balearic Island where organized DMC development is more promising. Air masses that will overcome the cap over continental Spain may become severe as bulk shear 0-6km exceeds 20 m/s with SREH0-3km over 200 m²/s². Moreover, steep mid level lapse rates increase the large hail potential.
.... Balkans ....
We expect diurnally driven thunderstorms, except from the early morning storms in NW Aegean where the main threat will be waterspouts near the coasts as the SST-T850hPa difference is more than 12°C, the LCL heights will be below 800m and LLS has values between 6-8 m/s. Later in the afternoon, pulse storms are forecast to remain almost stationary, except from N Greece - FYROM and south-most parts of Greece, and excessive rainfall will be the main risk. Given the dry PBL - high LCLs and 15-17 m/s of DLS in South Greece, large hail is expected within the most organized cells. Activity will fade after sunset.
