Storm Forecast
Valid: Wed 25 Jun 2008 06:00 to Thu 26 Jun 2008 06:00 UTC
Issued: Tue 24 Jun 2008 22:05
Forecaster: GATZEN

SYNOPSIS

A subtropical high over northern Africa ridges into central Mediterranean, while low geopotential extends from Scandinavia to eastern Atlantic. At the northern flank of the ridge, a very strong jet stream is located from northern Bay of Biscay to the Baltic States. At lower levels, an intense frontal boundary will be located from Bay of Biscay to central Germany and further to the Black Sea.

DISCUSSION

Southern Germany, northern Alpine region, Czech, Slovakia, Austria

South of the main frontal zone, a weak upper short-wave trough travels eastward over north-western Mediterranean. Models indicate that a mid-level jet streak will eject northward into southern Germany during the period, providing some QG forcing. At low levels, both GFS and ECMWF indicate that a low will develop over Germany that supports intense warm air advection along the warm front that will likely be located from western Alps to central Germany during the day. While dry air mass will be present over northern Germany, it seems that rich low-level moisture that will remain north of the Alps will advect northward. Latest observations show that convection goes on in the range of the frontal boundary underneath the upper jet streak, and may likely merge into an MCS moving into south-western Germany until WED, 6 UTC. During the day, initiation is most likely south of the warm front, where low-level convergence is expected. Current scenario is that thunderstorms will spread eastward during the day underneath the cyclonic flank of the upper jet streak. Given quite strong forcing, thunderstorms may merge into an MCS moving eastward into southern Poland and Czech Republic. To the south and east of the main MCS, more isolated cells are forecast from eastern France to Germany, northern Alpine region, Austria, and Czech in the afternoon hours. Given moderate vertical wind shear, large or very large hail is not ruled out with the stronger storms. Additionally, severe wind gusts may occur. Along the frontal boundary, locally large SRH values and stronger DLS will be more favorable for rotating and long-lived updrafts, while limiting factor is uncertainty of low-level moisture as well as daytime heating and resulting CAPE. This may lead to more elevated convection and limited severe threat. However, models seem to agree that sufficient instability will develop, and this may result in supercells capable of producing large hail, severe wind gusts and local flash flooding. There is also a threat of tornadoes especially in the range of the frontal boundary where low LCL heights and rather high SRH values are forecast. Convection is expected to spread eastward into southern Poland and Slovakia during the night hours.

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