Storm Forecast
Valid: Sat 05 Sep 2009 06:00 to Sun 06 Sep 2009 06:00 UTC
Issued: Sat 05 Sep 2009 05:47
Forecaster: KOROSEC

A level 1 was issued for Adriatic sea towards southern Balkan peninsula mainly for large hail, strong winds, excessive rainfalls and lesser extent for tornadoes.

A level 1 was issued for parts of Romania and Ukraine mainly for large hail, strong winds and excessive rainfalls.

A level 1 was issued for SE Spain mainly for large hail and strong winds.

A level 1 was issued for areas from eastern Denmark towards the Baltic sea mainly for waterspouts.

SYNOPSIS

A deep trough continue its progress eastwards across the north-central Europe during the forecast period. A cold front is extending from Baltic states towards the southern Balkan peninsula. Frontal boundary is then curved WNW-wards towards the central Italy and Adriatic sea during the day, moving southwards and reaching southern Balkan by Sunday morning. Widespread convective activity is expected along this front. The main trough over southern Scandinavia transforms into an upper-level cut off low during the forecast period.

DISCUSSION

... Adriatic sea into southern Balkan peninsula ...

Convective storms will continue developing along the progressing cold front. With upper 10s to low 20s (Adriatic sea) surface dewpoints a moderate instability with MLCAPE near 1000 J/kg will become available ahead of the front, well overlaping with shear near 15-20m/s in the 0-6km layer. Storms will be capable to produce large hail, damaging winds and especially excessive rainfalls. Strong SW moisture flux will lead into strong orographic efects onto the mountainous terrain of SW Balkans and flash flood risk will be locally possible.

Especially over SW Balkans and Adriatic sea, strong Scirocco SE-erly winds will enhance SR helicity up to 250m^2/s^2, as well as LL shear to near 10m/s. Higher CAPE is also simulated over the warm waters of Adriatic sea, locally reaching close to 2000 J/kg. Storms in these areas will tend to be better organized with low-level rotating updrafts as well. Therefore a couple of tornadoes 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.

... parts of Romania and Ukraine ...

During the late morning hours, the trough axis approaches and large scale ascent ahead of it will initiate storms along the frontal boundary. About 500-1000 J/kg of MLCAPE will result by diurnal heating and steepening lapse rates aloft. Within the right jet entrance, near 15m/s of deep layer shear seems likely. Up to 200m^2/s^2 of SREH3 should be available along the front as well. While GFS tends to have higher instability than ECMWF, both simulate good overlaping of instability and shear/SREH. Therefore, organized storms including strong multicells and a few supercells will be possible. The main threat will be large hail and excessive rainfalls. Given the aforementioned enhanced SREH, LL mesocyclones could also form. But limited LL shear gives only low chances for a funnel/tornado formation.

... SE Spain ...

Several hundreds J/kg of MLCAPE seems likely to release in the afternoon as result of returning moisture from the sea onshore. GFS shows a convergence mostly along the mountains and storm initiation is expected there. Near 15-20m/s of deep-layer shear seem enough supportive for a couple of severe storms and therefore level 1 threat level was issued for these areas. Given the high values of delta theta-E, strong wind gusts are possible, as well as few large hail events.

... eastern Denmark towards the Baltic sea ...

Polar airmass within the large trough overspreads these areas while the trough slowly cuts off into an upper-level low in the evening hours. Still warm waters of North and Baltic sea and steep lapse rates within the polar airmass will result in several hundreds J/kg of MLCAPE in weakly sheared environment. Numerous showers and thunderstorms will form ahead of the trough axis, mostly during the daytime hours. Slow moving storms and high LL lapse rates suggest that a couple of funnel clouds/waterspouts could form. A low-end level 1 threat was introduced for these areas.