Extended Forecast
Valid: Fri 15 Aug 2008 06:00 to Sat 16 Aug 2008 06:00 UTC
Issued: Wed 13 Aug 2008 21:18
Forecaster: TUSCHY

SYNOPSIS

Active weather pattern continues as a strong upper-level trough shifts to the east over central Europe. Ahead of this feature, pronounced WAA builds NNE-wards, resulting in very hot conditions over the central Mediterranean and E-CNTRL Europe. At the surface, a quasi-stationary frontal boundary is still in place, running from the Alpes over CNTRL Poland to W-Russia, separating the hot airmass to its east from the much colder and drier one to its west. This boundary serves as the focus for widespread thunderstorm initiation. Hot and stable conditions prevail over E/SE Europe and most parts of the Mediterranean.

DISCUSSION

** A major severe-weather event is forecast for parts of central Europe and an outbreak of severe thunderstorms with tornadoes, damaging wind gusts and significant hail can be expected. **

As this event is more than 24h ahead there still exist some uncertainties, which have impact on the final degree of severe thunderstorm coverage but tomorrow's Severe Weather Day-1 Outlook will go into more details.

A potent and very dynamic upper trough crosses France during the morning hours and draws near the Alpine region during the afternoon hours. Accompanied by an extreme wind field, shear improves constantly south and later also east of the Alpes with awe-inspiring 35-40 m/s 0-6km bulk shear values over the northern central Mediterranean. During the afternoon and evening hours, shear also increases significantly E/NE of the Alpes, with 0-6km DLS values of 25-35m/s all the way to N-Poland. Regarding the shear profilers at LL, the final strength of a surface depression will be crucial and model pool still has a bad handling on this feature. However, latest GFS runs f.ex. showed 0-3km shear of 25-35m/s, LL shear of locally up to 20m/s and also very high SRH values, maximized over Poland, but also augmented all the way down to the N-Adriatic Sea. The highest values should be confined along a complex and undulating frontal boundary, retransforming into a warm front over Poland and a cold front over E-Austria/Czech Republic.

Very rich BL moisture and steep mid-level lapse rates along the front result in near 1000 J/kg MLCAPE, with locally higher MUCAPE values. Areas too far to the east of the frontal boundary stay capped, as very warm temperatures at 850hPa (22-25°C) are present in the warm sector. Another interesting point is abundant LL CAPE release along the boundary, which could be a backing mechanism for tornado development, which has to be monitored in the upcoming model runs.

Forecast soundings from central Italy to Poland indicate that the environment is prime for tornadoes/a few strong ones/large hail/a few damaging events included and severe to damaging wind gusts. Those areas were included into a level-2. Another concern is the flash flood risk, as background flow component is more or less parallel to the surface front east/northeast of the Alpes in addition to very high LL mixing ratios, which are also forecast along this boundary. Thunderstorm coverage and intensity will diminish during the night, although atmosphere should stay conducive for a few severe events mainly over the northern level areas and along the N-Adriatic Sea.