Storm Forecast
Valid: Wed 06 Jul 2011 06:00 to Thu 07 Jul 2011 06:00 UTC
Issued: Tue 05 Jul 2011 22:09
Forecaster: PUCIK
A level 1 was issued for Southeastern France, Northern Italy and Slovenia mainly for large hail and severe wind gusts.
A level 1 was issued for Southwestern Germany mainly for large hail.
A level 1 was issued for Northeastern Poland, Western Belarus, Eastern Baltics and parts of Russia for excessive precipitation.
A level 1 was issued for Central Ukraine mainly for excessive precipitation, large hail and to lesser extent for tornadoes.
SYNOPSIS
At midlevels, a large cyclonic vortex is observed over Atlantic, centered over the British Isles. The vortex will slowly progress eastwards and two vorticity maxima are forecast to rotate around it. Strong flow surrounds the vortex, especially at its southern and southwestern flank. Another, albeit shallower, vortex has been stagnant over Eastern Europe for several days as of today and should be centered over Ukraine, slowly filling and moving northwards. Between these two features, insignificant ridge of high pressure is simulated.
Closer to the surface, situation is very similar with two lows dominating the weather pattern over much of Europe. Complex frontal system lies over Eastern Europe, weakening as the low fills in during the forecast period, but with an important warm conveyor belt on the eastern, northern and northwestern flank of the low. To the west, a cold front will slowly progress across Western Europe.
The best conditions for thunderstorms will prevail over Southeastern and Eastern Europe, where moist and warm airmass at low levels, in conjuction with cool mid-levels act to destabilise conditions. Another focus for thunderstorms will be a prefrontal region ahead of the progressing cold front mentioned above.
DISCUSSION
... Northeastern Spain ...
Both GFS and ECMWF simulate built up of some marginal to weak CAPE and thanks to the strengthening flow aloft, overlaping with moderate to strong wind shear. Nevertheless, at the moment, initiation seems to be unlikely owing to the very high CIN values and threat too low to warrant a Level 1.
... Southeastern France / Northern Italy / Slovenia ...
Models agree on the development of moderate degree of instability, with most common values of MLCAPE above 1000 J/kg in this region. Diffluent flow and slight PVA advection suggest some synoptic support for the destabilisation and local convergence zones tied to the orography are expected to initiate thunderstorms. The highest coverage of storms is expected over Northwestern Italy. With strenghtening flow aloft, moderate DLS is predicted with values ranging from 15-20 m/s, the westernmost parts even exceeding 20 m/s. Ahead of the cold front over Southeastern France, ageostrophic component of the flow might result in enhanced SREH values. In such setup, locally well organised convection is forecast, including possibility of brief supercells with threat of predominantly large hail. Enhanced Delta Theta-E values also point to the possibility of marginally severe wind gusts with stronger downdrafts. Thus, a Level 1 is introduced for the region.
... Southwestern Germany ...
Similar conditions to Northern Italy are forecast for the region, possibly with slightly lower CAPE values but the storm coverage is more questionable over this area, with ECMWF and Aladin producing very little precipitation over the area, in contrast to WRF and GFS. Moreover, less of an overlap between strong shear and instability will exist. A marginal Level 1 is introduced for a slight threat of a large hail but if initiation proves to be less likely during the day an update regarding the Level termination might become necessary.
... Northeastern Poland / Western Belarus / Eastern Baltics / parts of Russia ...
In the warm and very humid conveyor belt of the low, rather weak easterly to northeasterly flow prevails. Very high relative humidity at lower levels, combined with high effective precipitable water values point to the possibility of excessive rainfall, especially if rather slow storm motion is taken into the account. Therefore, a Level 1 is introduced for a belt, where local threat will exist.
... Central Ukraine ...
Ahead of the surface cold front, warm and humid airmass is located. As a mid and upper level PVA max crosses the region, destabilisation is forecast, along with strengthening wind field. In resultant, a favorable overlap between moderate instability and moderate to strong wind shear might develop (locally over 20 m/s of DLS). High coverage of storms is expected, possibly in form of a large multicellular complex with threat mostly of an excessive precipitation. Stronger cells, especially in case that supercells manage to develop, might produce large hail. Towards the evening hours, low level shear is also forecast to strenghten, especially over the northern parts of Level and together with low LCLs, point to a slight threat of tornadoes.
