Storm Forecast
Valid: Tue 08 Aug 2006 06:00 to Wed 09 Aug 2006 06:00 UTC
Issued: Mon 07 Aug 2006 21:38
Forecaster: TUSCHY

SYNOPSIS

A broad and very dynamic pool of low geopotential heights is still placed over most parts of Europe.... While one trough is forecast to dig southward over the central Mediterranean, another trough will continue to lift out towards the NNE over eastern Europe....
An intense cold front should reach Scotland and Ireland during the night hours... Right now, there are no indications of any significant convective activity along this front and hence don't want to include this area in a TSTM area.

DISCUSSION

... N-Algeria and Tunisia...

The first well pronounced influx of cooler mid-level air over the still very warm western Mediterranean will occur during the next 24 hours .
An intense upper-level jet core ( winds up to 110 kt ), which crossed Ireland, United Kingdom and even NW France yesterday, will continue its southward shift.... A yet not well defined upper - level trough over western Europe will continue to amplify due to the arrival of the upper - level jet.
Latest sounding datas (Brest 12Z ), wind profilers and IR/WV loops indicate, that models like GFS do a good job with the jet location...
Due to the strong amplification towards the south, baroclinity / a strengthening gradient in the geopotential height fields will support the development of another intense jet max along the tip of this trough ( over N-Algeria/Tunisia ).
The whole jet configuration will support a quick shift from a positive towards a neutral trough axis location.... This fast displacement of the trough axis makes it possible, that a pool of cool air (-15°C at 500hPa ) will cross the distance SW France - N-African coast in about 24 hours, which in turn will be favorable for a broad area with moderate to high instability release ( remembering the SSTs of 25-27 °C south and east of Majorca ).

The first area of interest will be the level - 1 area.... During earlier cases, TSTM development over N-Africa was affected a few times by the very dry continental airmass further towards the south.... Streamline analysis indicates only a shift from the NW towards the W of the mid-upper level wind field and no development of a significant low-level depression.... So right now, there are no indications of any influx of desert air.
Intense forcing and a slight cool down of the mid-levels should support isolated to scattered TSTM development over the mountainous areas of N-Algeria and Tunisia....
Still very warm 850hPa temperature will be present ( mainly over Algeria) // and hence a pretty stout cap //, but indications are that they will also cool down during the late afternoon hours mainly over Tunisia.... If this in fact verifies , scattered TSTMs will develop / go on over N-Tunisia in an environment with 20-25m/s DLS.... There will be mainly a severe wind gust risk, especially, when a line of storms could form.

Further towards the north, instability values up to 2000 J/kg SBCAPE will be possible.... Strong NNW flow ( with a possibly well developed Mistral ) should suppress any significant convection north of Majorca and the question will be, how far towards the south this desiccated airmass will be advected.... Increasingly warm SSTs and very steep lapse rates should support the development of scattered TSTMs in the highlighted areas... This will be a typical high CAPE- weak shear environment with an isolated large hail and mostly sub-severe wind gust threat... Although not impressive, conditions could even become fine for an isolated funnel / tornado report ( mainly along mesoscale boundaries ).

....Most parts of the Ukraine and extreme S-Russia...

A developing low-level depression (over N-Ukraine ) downstream of a slowly NNE-ward shifting upper-level trough will be the focus for scattered TSTM development.... The main activity will be east of our area of responsibility ( due to the displacement of the strongest DLS ).
Still...a small area over NE Ukraine has up to 15m/s DLS and 10-15m/s low-level shear in an environment with low LCLs..... Even high-resolution global models indicate a well defined backing wind field and hence conditions will be favorable for a few tornadoes, severe wind gust and large hail reports.... Main uncertainty will be the exact placement and strength of the low-level depression and therefore only a level-1 was issued, but the area could be upgraded later-on.

Further towards the west, enhanced LL shear / 0-1km SRH values still indicate the possibility for one or two tornadoes ( in an environment with pretty low LCLs ), but weaker DLS should restrict the large hail/ severe wind gust threat.