Storm Forecast
Valid: Wed 01 Oct 2008 06:00 to Thu 02 Oct 2008 06:00 UTC
Issued: Wed 01 Oct 2008 05:39
Forecaster: PUCIK
SYNOPSIS
Dominant feature of the day will be a large surface low affecting most of the northern and central parts of Europe, only slowly moving to the east. By the end of forecast period, it will have deepened sligtly with center over the Baltic sea. Its strong pressure gradient will likely induce widespread wind gusts, especially across the southern parts of the Northern Sea, Great Britain, BENELUX and Germany. A cold front, associated with the low will stretch from the northern France to Poland and continue east/southeastwards. At midlevels, a deep trough has settled over the region of the surface low. It is dominated by a cold airmass, yielding high mid-level gradients due to the warming effects of the sea. Strong jet-stream will spread on its southern flank to the east, with 40 m/s at 500hPa level. Trough is forecast to deepen, especially over the the E Atlantic / British Isles and move to the SE . Another shallow trough will slowly fill over the Algeria/Tunisia region.
DISCUSSION
...Northern sea, coasts of Denmark, S Norway, Netherlands...
Slightly unstable conditions are forecast over the Northern sea, with MLCAPEs locally higher than 500 J/kg. Moreover, profiles should remain uncapped with significant low level buoyancy and lapse rates. Moist environment over the sea will lead to the low LCLs of developing storms. Therefore, threat of waterspouts will be present and a Lvl 1 is warranted. Highest risk is anticipated over the western coast of Denmark, where GFS simulates strong convergence signals, as well as strong mid-level forcing, supporting the storm development.
...N Germany, N Poland...
Models count only with very little instability available for the storms, with MLCAPEs around 200 J/kg. However, very strong mid-level forcing is expected, which could help in the storm development in spite of the meager instability. Strong low level wind field is forecast across the region, especially by the noon with 20 m/s of shear in 0-3 km layer and 15 m/s of shear in the lowest km. 850hPa windspeeds should be approximately 20 m/s. 00Z soundings support above mentioned predictions, as slightly unstable profiles are observed over the region as well as strong LLS. Current thinking is that either a strongly forced convective line or a series of separate cells will move over the region, with threat of isolated severe gusts, exceeding 25 m/s. Also thanks to the favourable LLS, moist boundary layer and considerable SREH present 0-1 km ( values exceeding 200 J/kg), one or two tornadoes are possible. The highest threat will exist around 09-12Z, across N Germany when strongest forcing and wind fields will be available.
...SE Ionian Sea, W Greece coast...
Both surface and mid-level trough will support the TSTM initiation. Moderate instability is predicted across the region with MLCAPEs locally above 1000 J/kg. Strong mid level flow will be induced by the trough, resulting in approximately 15 -20 m/s of DLS and 10 - 15 m/s of shear in 0-3 km layer, especially over the SW coast of Greece. Also, slight backing of the surface flow ahead of the trough will lead to the enhanced SREH. Environment seems to be supportive of well organised storms, mostly multicells, but supercell is not ruled out either. Marginally large hail is possible in stronger storms. Due to the significant LL Cape release, especially near the coast and low LCLs, few waterspout / tornado reports are expected. Also, thanks to the strong moisture convergence and widespread TSTM initiation, flash flooding threat will exist.
