Extended Forecast
Valid: Thu 14 Aug 2008 06:00 to Fri 15 Aug 2008 06:00 UTC
Issued: Tue 12 Aug 2008 21:29
Forecaster: TUSCHY

SYNOPSIS

A potent upper trough over NW Europe moves to the east and dictates the weather over most parts of Europe. A hot airmass advects northeastwards from N-Africa and very hot conditions impend the central Mediterranean. Along a wavy, quasi-stationary front, running from SE-France to extreme NW-Russia, thunderstorms are forecast and as strengthening wind field arrives during the evening hours, organized thunderstorms can be expected south of the Alpes. Unsettled but warm conditions exist over NE Europe under the influence of a departing upper trough.

DISCUSSION

... N/N-CNTRL Italy, Slovenia and Austria ...

Downstream of an eastward moving upper trough, still placed over NW Europe during the evening hours, strong WAA is on its way tot he NE , overspreading those areas during the day with rich BL moisture in place during the evening and night hours. At the same time, a plume of steeper mid-level lapse rates approaches those areas during the evening hours, so regarding instability release, widespread 500 - 1000 J/kg MLCAPE can be expected with foci over N-CNTRL Italy and the northern Adriatic area, decreasing over Austria. An intense jet rounds the base during the day and will arrive during the evening hours from the SW, enhancing DLS values in the lowest 6km to 30 - 35m/s. As winds veer throughout the atmosphere, resulting in very high SRH-3 values, rapid storm organisation can be expected and supercells will likely produce large hail and severe wind gusts. The main severe thunderstorm event will start during the evening hours, but as a few weak short-waves already cross the area during the day, a few thunderstorms during the daytime hours can't be ruled out.

Instability release decreases over S/E Austria but overall conditions are fine for thunderstorm development and this event could consist of numerous surges with the most active one also during the night hours, as thunderstorms spread NE-wards from NE-Italy/Slovenia. DLS increases constantly to near 30m/s during the early morning hours over S-Austria and a few large hail events can occur. In addition, latest GFS run showes a rapid increase in LL shear to more than 10m/s / near 200m^2/s^2 SRH-1. Later outlooks have to evaluate the tornado risk, which could be augmented, if storms from the south stay surface-based.

A level-2 was issued for those areas, where latest model runs had persistent signals of supercells with an isolated significant hail threat but modifications will be needed in later outlooks.

... Finland and extreme western Russia ...

A NE-SW elongated trough slowly lifts to the east/northeast and a combination of a humid BL airmass and cool mid-levels result in widespread 500 - 800 J/kg MLCAPE. LL shear is enhanced with some directional shear and as LCLs stay low, there is the risk of a few tornadoes. Parts of this highlighted area may need an upgrade later-on.

... NE Spain and the area N of the Balearic Islands ...

As the trough axis approaches during the evening hours with intense forcing, thunderstorms are forecast to develop, spreading very fast to the east as DLS increases to 35m/s. Large hail, severe wind gusts are possible with those thunderstorms.