Storm Forecast
Valid: Sat 16 May 2015 06:00 to Sun 17 May 2015 06:00 UTC
Issued: Fri 15 May 2015 19:43
Forecaster: DAFIS

A level 1 was issued for north Bulgaria and south Romania for marginal hail and severe wind gusts.

A level 1 was issued for Italy, parts of Tunisia and NE Algeria mainly for severe wind gusts, large hail and excessive rainfall.


SYNOPSIS

The main synoptic characteristic for today's outlook is the cut-off low pressure system and its symmetric cold-core vortex that is dragged over the quite cold central Mediterranean with SSTs of roughly 17-18oC. Southern parts of France, around gulf of Lyon, will experience wind gusts up to 25m/s due to LL convergence of NW flow in the area. During the day, a cold front will cross Italy favoring the development of thunderstorms in mainland parts mainly during the evening. Moreover, some persistent and well organized storm cells are forecast to affect northern Sicily's shore during the night of Saturday. For Bulgaria and southern Romania, LL convergence is forecast as warm and unstable air masses move NE and very steep lapse rates will favor the development of rapidly forming storm cells. We have to mention the significant amount of dust load from Sahara desert over south Italy and Balkans that will probably affect the convective initiation.

DISCUSSION

... Central Mediterranean ...

The moving depression pushes a cold front east which comes ashore the central and south Italy during the early morning of Saturday. For the area of Sardinia there is not much shear/CAPE and moisture to work with, so pulsating storms are expected, which will grow upscale into numerous disorganized clusters with heavy rain and gusty winds. Sardinia could see excessive rain, both due to prolonged upslope flow and later-on also due to slow moving thunderstorms (placed beneath the center of the vortex). Also in Tunisia and NE Algeria, to less extend, excessive rainfall is expected due to unstable air masses approaching from Mediterranean, pushed by the aforementioned depression. During the night of Saturday and early morning of Sunday, 25-30m/s DLS, 1000j/kg MLCAPE, 300m2/s2 SHR3 overlap, so supercells are expected to form with low-level rotating updrafts as well. Therefore a couple of waterspouts can form, especially near the intersections of pre-frontal convergences where even higher SREH can build. A threat for few large hail events and strong winds will exist with the strongest cells as well. In NW Italy a strong SE moisture flux will lead into strong orographic effects onto the mountainous terrain so excessive rainfall will be locally possible.


... Bulgaria and south Romania ...

A weak mid-layer impulse lifts to the NE atop BL mixed layer mixing ratios of about 7-10 g/kg. The highest CAPE values are simulated over Bulgaria, where the best overlap of low-level moisture and EML is likely and diurnal heating and the presence of a very humid airmass, with dew points over 18°C shown by models for the region, should lead to the release of 1500-2000 J/kg of MLCAPE. The low-layer lapse rates steepen to 18-20 K/km indicating superadiabatic conditions. A few short-lived thunderstorms are forecast but large values of CAPE suggest that any well organized cell will have a potential to produce large, or even very large hail and severe wind gusts. The activity wanes after sunset.


..... Rest of Europe ..........

For the rest of Europe either instability or shear or both are too weak for long-lived, organized convection so no severe risk is forecast. Although, the moist BL with steep lapse rates during the evening in Serbia/Bosnia and Herzegovina and MLCAPE of about 1000J/kg are good indicators of marginal thunderstorms whilst strong wind gusts might occur with wet microburst activity over this area.