Storm Forecast
Valid: Mon 14 Apr 2008 06:00 to Tue 15 Apr 2008 06:00 UTC
Issued: Sun 13 Apr 2008 21:03
Forecaster: GROENEMEIJER
...Corrected small errors 22:02 UTC...
SYNOPSIS
Monday at 06:00... a longwave trough with several embedded shortwave troughs is located over western Europe. One shortwave trough extends from the North Sea over northwest France into the Bay of Biscay. Downstream of this feature, a westerly jet streak over northern Spain into the western Mediterranean will move eastward. A shortwave trough further downstream has its axis from central Italy via Sicily to northwest Lybia. Over southeastern Europe a Saharan mixed layer is flowing northward, its western edge being formed by a front stretching from northeast Lybia to the eastern Peloponnese to eastern Bulgaria. A frontal wave and subsequent cyclogenesis is over Bulgaria in the second half of the forecast period as the Italo-Lybian shortwave starts to interact with the frontal zone.
DISCUSSION
...Sardinia...
Numerical guidance suggests that the mid/upper jetstreak will intensify and its left-exit region with associated upward vertical motion will cross Sardinia during the late morning and early afternoon. With rather moist low-levels and near moist-neutral stratification in place beforehand, some 400-800 J/kg of uncapped CAPE could easily result. Convective storms are expected to develop during the latter half of the morning. Given that near 25 m/s deep-layer shear is being forecast, some cells may develop rotating updrafts. This could result in some hail - possibly exceeding the severe threshold. As low LCL and LFC levels are forecast, and low level shear is supportive, the development of an isolated tornado cannot be ruled out.
...Low Countries, Lower Saxony, the Rhineland, northern France...
In a weak northwesterly flow regime, rather moist air is expected to destabilize in reaction to solar heating and a subtle shortwave approaching from the North Sea. As a consequence, about 300-600 J/kg of CAPE will likely form. Cloud bases and LFC are expected to be particularly low, suggesting that near-ground upward parcel accelerations will be strong and a few weak, spout-type tornadoes may occur. Overall cool conditions will also favour rather widespread small hail, including some hail in the 1-2 cm range. Convective activity will gradually diminish after dark.
...Northern Dinaric Alps/ western Pannonian Plain...
Parts of Slovenia, SE Austria, W Hungary, Croatia and Bosnia will also see rather intense diurnally-drive convection, despite shear being weak. Some hail approaching the severe limit of 2 cm is possible in stronger storms. The development of an isolated weak spout-type tornado cannot be ruled out either.
...NW Turkey, Tracian Plain into the Danube Delta...
Currently numerical guidance from GFS and AFWA MM5 consistently produce very little, if any, convective precipitation over the area and very little CAPE. If more moisture is present at the top of the boundary layer than currently forecast, some elevated (thunder-)storms may form producing some hail. Overall severe weather threat however appears low.
