Storm Forecast
Valid: Tue 06 Jul 2010 06:00 to Wed 07 Jul 2010 06:00 UTC
Issued: Mon 05 Jul 2010 22:54
Forecaster: KOROSEC
A level 1 was issued for parts of Northern Italy towards northwestern Balkans mainly for excessive convective rainfall, large hail and strong wind gusts.
A level 1 was issued for much of Ukraine, extreme NE Romania, northern Moldova and across Central Russian Upland mainly for excessive convective rainfall and isolated large hail.
A level one was issued for Baltic states, western Belarus, eastern Poland and eastern Slovakia mainly for excessive convective rainfall and marginally large hail.
SYNOPSIS
A progressive trough continues moving eastwards across central Europe while becoming negatively tilted. It then slowly transforms into upper low by Wednesday morning and merges with another upper low over eastern Europe. Another deep trough with a strong surface cyclone and an attendant frontal system approaches UK. A weak upper-level low located west of Marocco on Monday slowly shifts northwards. Despite the improving shear over SW Iberia, strongly capped environment will again preclude initiation of deep convection there.
At surface, a weakening/diffuse cold front moves SE-wards from central Europe towards eastern Europe and northern Balkans where convective activity and well organized severe storms will be possible.
DISCUSSION
... north Italy towards northwestern Balkans ...
Hot and moist airmass with 10-13 g/kg mixing ratios is placed ahead of an approaching trough/diffuse surface front across northern Mediterranean and northern Balkans states. It seems that around 1000-1500 J/kg of MLCAPE (locally over northern Italy even exceeding 2000 J/kg) will be available by the time of storms intiation. Weakly capped environment should hold the convection until the early afternoon hours when CINH erodes. Initiation is first expected along the southern Alpine flank where convergence will be placed. Storms will then move SE-wards into better environment. At this time, moderate mid-level jet streak across the Alps provides some QG forcing and deep-layer shear of 15-25m/s which should support organized severe storms. Organized multicells and a few rotating storms will be possible, especially where LL easterly/backing flow could enhance SR helicity. With rather high LL moisture inflow and around 15 K of delta theta-E, a threat for excessive rainfall and strong wind gusts will exists. The stronger cells could support large hail as well, especially if they manage to be more discrete and therefore more organized, likely acting as supercells. Towards the late afternoon, a cluster of storms/a small MCS is possible from the earlier activity, moving southeast. Parts of northern Italy were included into level 1 especially for excessive convective rainfall threat given the high PWAT and delta theta-E values.
Some uncertainities exist for the storm's coverage, where local models and ECMWF have larger coverage than GFS and WRF. A level 1 was extended eastwards across SE Austria, E Slovenia and W Hungary as it seems better ascent beneath the left-exit jet region will be enough to root deep convection and threat for well organized storms also over the western Pannonian plain. Areas including NE Italy and much of Slovenia will be closely monitored for a possible upgrade into level 2 tomorrow if higher probabilities for more widespread coverage of organized severe storms exist than is currently anticipated.
... Baltic states, western Belarus, eastern Poland and eastern Slovakia ...
Ahead of a moving surface front, around 1000 J/kg MLCAPE builds up. It seems that at least some forcing will exist and storms are expected to form along the moving surface convergence in late morning hours. While limited shear exists, likely multicells with excessive rainfall and some marginally large hail will be possible. A clustering into a large system or two later in the afternoon/evening hours is possible along the moving trough axis.
Baltic region will mostly see daytime driven convective activity, slow moving and pulsating storms as shear remains beneath 10m/s. A threat for mainly excessive convective rainfall exists there. A level 1 was therefore placed where this threat seems maximized.
... Ukraine, extreme NE Romania, northern Moldova and central Russian Upland ...
Another day under the large upper-level vortex and with high LL mosture and instability over these areas. With only weakly capped airmass and very limited shear, numerous multicells or larger clusters are expected to be on going by the noon and continue until the evening hours. Their slow moving and rather explosive pulsating nature should pose a threat for excessive convective rainfall and local flash floods, as well as some isolated strong wind gusts. Deep layer shear seems slightly better over Eastern Ukraine and Central Russian upland which could result in better organized storms, posing a threat for isolated large hail event or two.
