Storm Forecast
Valid: Mon 11 Sep 2017 06:00 to Tue 12 Sep 2017 06:00 UTC
Issued: Sun 10 Sep 2017 20:30
Forecaster: DAFIS

A level 2 was issued for Italy, S Croatia, Bosnia and Herzegovina, Montenegro, Albania and Greece mainly for severe wind gusts, large hail, excessive precipitation and tornadoes.

A level 1 was surrounds the level 2 area for the main threats with lower coverage.

A level 1 was issued for E Austria, Czech Rebublic, Hungary, E Slovakia, Poland and Belarus mainly for excessive rainfall, severe wind gusts and large hail.

SYNOPSIS

A very interesting weather pattern has formed over Europe, with numerous mid-level waves, strong instability in the southern parts and organized baroclinic systems near the surface. During Monday, a cut-off low will be formed over Italy with a wrapped jet stream around the center of the system, increasing the deep layer shear to extreme values. Mediterranean Sea has the highest SST of the year now, and very moist air masses from Ionian and Adriatic Seas will be advected on-shore. Another long-wave trough over North Sea results in some instability and a quasi-stationary front near the surface in E Europe creates favorable conditions for convective phenomena.

DISCUSSION

.... Italy, Croatia, Bosnia and Herzegovina, Montenegro, Albania and Greece .....

During the early morning of Monday, we expect a cold front to move eastwards from Italy, where a first round of organized thunderstorm activity will take place, possibly in a form of a squall line. Even though storms will move fast, flash flood events cannot be ruled out. Locally strong convergence zones at the coasts of Adriatic Sea and strong SW mid-level flow will steer the storms, which will propagate to the east. GFS predicts a tropical-like plume of air masses with mixing ratios up to 18 g/kg and 2-3 kJ/kg MLCAPE. DLS will reach extreme values both over land and sea, increasing the probability of very strong storm-cells able to produce all kinds of severe weather. Apart from 25-35 m/s DLS, 0-3km shear will also reach extreme values up to 30 m/s, showing a conducive environment for supercells, producing severe to extremely severe wind gusts. The storm mode over the sea is expected to be linear, but more isolated cells over the land can produce large hail. Tornado threat is also increased due to strong LLS overlapping with high SBCAPE. Moreover, waterspouts are expected at the cold sector of the front.

.... E Austria, Czech Rebublic, Hungary, E Slovakia, Poland and Belarus ....

A quasi-stationary front over this area partially overlaps with a mid-level jet streak, resulting in organized storm activity, mostly driven by diurnal heating. Global models show rather weak mid-level lapse rates, so CAPE only locally exceeds 1 kJ/kg. Slow-moving storms may produce excessive precipitation and more isolated cells can produce large hail and severe wind gusts. In addition, strong LLS will increase tornado threat between 12z and 15z, as long as the storms will be surface-based. Non-severe storms are expected to continue during the night due to elevated convection.