Storm Forecast
Valid: Wed 28 May 2014 09:00 to Thu 29 May 2014 06:00 UTC
Issued: Wed 28 May 2014 13:05
Forecaster: PUCIK
A level 1 was issued for N Italy, Slovenia, W Hungary, E Czech Republic, Slovakia, S Poland, Ukraine, Belarus, NE Romania and parts of Russia mainly for excessive precipitation and to the lesser degree for marginally large hail and severe wind gusts.
A level 1 was issued for E Algeria and Tunisia mainly for large hail and severe wind gusts.
A level 1 was issued for Central Spain mainly for large hail and severe wind gusts.
SYNOPSIS
Not much of a change has occurred to the synoptic situation since the last period. Rather weak geopotential fields are forecast over much of Central Europe, apart from benign low at mid and upper troposphere, that is centered over Austria as of Wednesday 06 UTC. It is forecast to slowly fill in, without any significant movement. Another low will slowly sag southwards from Finland toward the Baltic States. Perhaps a more active pattern is forecast over the southern extent of the forecast area, where a trough will cross over the western Mediterranean. To the south, over extreme N Africa and the S Mediterranean, strong mid to upper tropospheric flow is simulated.
DISCUSSION
... Italy, Slovenia, Western Hungary, Slovakia, Czech Republic, Poland, Ukraine, Belarus, Romania ...
Soundings from Tuesday 12 UTC and Wednesday 00 UTC reveal continuing pattern featuring moist boundary layer with low LCLs, skinny CAPE profiles, rather weak steering flow and precipitable water values between 25 and 35 mm. No major change is expected to occur in the following hours. Marginal to moderate CAPE will quickly develop as daytime heating commences and CI should not be an issue with no capping layer present. Most of the development will likely be tied to the
A/ orography
B/ convergence zones. The most prominent one is simulated from Bohemia towards S Poland, Belarus and further NE-ward.
With weak flow, chaotically organised multicell clusters are forecast (parts of the Czech Republic and S Poland may see slightly enhanced wind shear thanks to the position to the north of the mid-tropospheric low), tied to the local convergence zones and outflow boundaries. In case that training pattern develops, excessive precipitation will be likely thanks to the environment favouring highly effective rainfall. Especially in the areas that already experienced heavy rainfall, pronounced flash flood risk will be present. Besides the heavy rain, marginally large hail may occur with stronger cells.
... Western Russia (east of the Baltic States) ...
Being situated on the forward flank of the low, stronger mid-tropospheric flow will allow for moderate to strong degree of vertical wind shear, with DLS values between 15 and 20 m/s. However, only marginal CAPE is forecast, so that some low topped multi / supercells may produce some marginally large hail and severe wind gusts besides the locally excessive precipitation.
... Eastern Algeria / Tunisia ...
As the trough crosses region, strong DLS is forecast with marginal to moderate CAPE. Rather favourable overlap of instability and shear should prove sufficient for well organised DMC, including some supercells, capable of large hail and/or severe wind gusts. Possible storm clustering towards the evening might result in an excessive precipitation event.
... Central Spain ...
In the strong northwesterly flow aloft, DLS between 20 and 30 m/s is simulated by models, already sufficient for well-organised DMC, including supercells. However, models are not very optimistic regarding the degree of instability - both ECMWF and GFS produce CAPE on the order of hundreds J/kg. PVA along with some low level convergence should aid in the iniation of isolated to scattered DMC with stronger cells possibly capable of large hail and severe wind gusts (taking into the consideration high LCLs in this region). Towards the coastline, isolated excessive precip event is not ruled out either!
