Storm Forecast
Valid: Sun 10 Jun 2012 06:00 to Mon 11 Jun 2012 06:00 UTC
Issued: Sun 10 Jun 2012 04:27
Forecaster: PUCIK

A level 2 was issued for Central Ukraine mainly for large hail, severe wind gusts, tornadoes and excessive precipitation.

A level 2 was issued for E Hungary, W Romania, E Slovakia and extreme NE Serbia mainly for large to very large hail and severe wind gusts.

A level 1 was issued for E Austria, Hungary, E Croatia, Central Serbia and Central Romania mainly for large hail and severe wind gusts.

A level 1 was issued for Slovakia mainly for excessive precipitation and large hail.

A level 1 was issued for Central to SE Poland and N Ukraine to S Russia mainly for large hail, excessive precipitation and tornadoes.

SYNOPSIS

An active weather pattern is prevalent over parts of Europe with a short-wave trough stretching from Germany into Italy, slowly moving E and a ridge over Southern Russia. Between these two features, brisk SW flow remains over much of Central, South-Central and northern parts of Southeastern Europe. A plume of EML is advected NEwards by this flow, contributing to the moderate to strong instability over the warm sector of a shallow surface low pressure system. As the short wave approaches this area, a surface low is expected to deepen and elongate towards the areas of W Hungary, Slovakia, E Czech Republic and S Poland with strengthening southerly flow to the east.

Currently as of 03 UTC, a large MCS slowly drifts NEwards over N Romania and SW Ukraine with extensive cirrus shield. 00 UTC soundings revealed strong instability and steep lapse rates, as suggested by Beograd ascent and strong DLS in all of the sounding sites to the north.

DISCUSSION

... Serbia, E Croatia through Hungary, W Romania, Slovakia into Poland, Ukraine and S Russia ...

Relatively good agreement between the NWP exists regarding these factors that will dominate the weather situation

A/ Surface low enhancing S-ly low level flow over Serbia, Hungary, Romania into Slovakia, Poland and Ukraine

B/ Plume of EML covering the southern part of this region

C/ Moderate to strong instability over the region, especially for Serbia, E Hungary, NW Romania and SW Ukraine, where MLCAPE values might very well exceed 2000 J/kg

D/ Warm front lifting across Slovakia, Poland and Ukraine during the day

E/ Moderate to strong DLS thanks to the SW-ly flow aloft, with the best vertical wind profiles south of the warm front with strongly enhanced SREH and DLS possibly over 25 m/s

Several uncertainities remain in the scenario and those are:

1/ Persistence of the morning MCS over Ukraine and its influence on the development there

2/ Remnants of the convection after very active previous day over Hungary might limit insolation somehow

3/ Contribution of the old outflow boundaries

4/ The northernmost extent of the warm sector

Current thinking is that storms will rapidly develop during the day, especially near the lifting warm front, where one or more MCS development over Slovakia, progressing into Poland and further into Ukraine is well possible relatively early in the day. We expect that northern part of the region will likely have the excessive precipitation as a major threat with humid low levels and very likely clustering of cells. However, strong DLS with bulk values of 20-25 m/s along with enhanced SREH locally over 300 J/kg might also turn any more isolated complex into a supercell with threats of large hail, severe wind gusts. Towards the evening, strengthening LLS with favorably veered flow above might in case of isolated supercells along the warm front easily lead to a few tornadoes in this location.

Towards the south, at first a more isolated development is expected, likely tied to the approaching short wave in the western extent of Lvl 1 and to the topographic features to the east. Also, capping will likely be stronger than to the north, which might help keeping DMC rather isolated and some areas might not experience DMC till late afternoon. In moderate to strong instability and DLS in the range of 15-25 m/s with enhanced SREH in the backing flow thanks to the deepening sfc low, strong well organised DMC is expected. Supercells will be likely with cell interaction and clustering later on probably resulting in a one or more MCS, which might included bow-echo structures. Large to very large hail and severe wind gusts are forecast for the region. With wind shear approaching 20 m/s in 0-3 km layer, steep lapse rates and drier low to mid levels of troposphere, isolated wind gusts over 32 m/s are not ruled out, especially later in the period. It is possible that e.g. Eastern Hungary will not see storms till late evening, but persisting strong instability and increasing DLS should maintain the risk.

A large Level 1 is introduced for the region, covering uncertainities mentioned above. A level 2 is outlined for the area, where the best agreement exists and which is expected to experience the highest probability of extremely severe weather. As the scenario becomes better definied in the noon hours, an update to the forecast might become necessary.