Storm Forecast
Valid: Mon 16 Oct 2006 06:00 to Tue 17 Oct 2006 06:00 UTC
Issued: Mon 16 Oct 2006 02:42
Forecaster: VAN DER VELDE

SYNOPSIS

Blocking high pressure area shifts from southern Scandinavia to Poland. Southwestern Europe becomes affected by a large low pressure area full of deep convection. An outbreak of cool air over the warm Black Sea along and behind a cold front will cause storms.
The Mediterranean/Ionean Sea upper longwave trough/surface low system continues to produce mesoscale convective systems in its region of warm air advection and good shear conditions.

DISCUSSION

...Portugal, western Spain...

A continuation of the situation that started yesterday, with the storms now moving deeper inland. GFS does not let MLCAPE continue far inland and solar heating is not strong anymore. The likely effect is a dilution of the coverage of storms over land. However, with more than 20-25 m/s DLS and more than 10-15 m/s LLS, storms may become supercells with a chance of large hail, perhaps some severe gusts, and tornadoes (LCL very low, under 500 m per GFS). Note that the forecast instability is best in the southern part of the level 1 region, whereas LLS and 0-3 km SREH (>200 m2/s2) are more enhanced over the northern half of the region.

...Ionean Sea into southern Aegean Sea...

In baroclinic conditions involving low level warm air advection and a slow-moving midlevel vorticity maximum near southern Greece, large storm systems continue.

The available MLCAPE is in the higher hundreds to over 1000 J/kg. DLS can amount to over 20 m/s, but these values do not overlap the model CAPE area - but 0-3 km SREH >150 or 200 m2/s2 partly does. Hence some storms can develop mesocyclones and enhance their potential to produce large hail. With 20 m/s winds at 3 km in MM5, there is indication of severe gust potential. Waterspouts are not ruled out. LCL heights are forecast to be lower than 1000 m, but LLS is not going to exceed about 8 m/s, limiting for a more serious tornado.

...Black Sea...

A (upper) low over the warm sea is expected to cause a lot of activity. Since moderate to strong values of DLS around the upper low overlap some CAPE, mostly off the map to the northeast, chances are that a few storms develop rotation that can induce tornadoes/waterspouts and large hail. Not much LLS will be present for a strong threat though.

...northwestern France, southwestern UK...

Not included in a thunder area, but some isolated lightning strikes have been located near the Channel with mininal signs of convective clouds. GFS and Hirlam do develop an area of convective precipitation, MM5 does not. Will likely remain very isolated in nature.