Storm Forecast
Valid: Thu 03 Jul 2008 06:00 to Fri 04 Jul 2008 06:00 UTC
Issued: Wed 02 Jul 2008 14:09
Forecaster: GATZEN

SYNOPSIS

Western Europe is affected by an intense trough. Its axis is expected from Ireland to south-eastern France on THU 12Z and will continue moving north-eastwards. Along the periphery of the upper trough, strong jet streaks exceeding 40 m/s at the 300 hPa level are forecast. To the east, a subtropical ridge amplifies over Europe and Scandinavia, where a closed high is expected to form as the trough axis moves into Central Europe. Over eastern Europe, another trough is present. At lower levels, dominating feature is a well-developed frontal boundary that moves across most of Germany and northern Alpine region during the day.

DISCUSSION

Southern Germany into northern Austria and Czech Republic

Cold front of west-European trough will enter Germany in the morning hours. Air mass east of the cold front is forecast to be unstable given rather rich low-level moisture and relatively steep lapse rates. Thunderstorms are likely along the cold front over the western portions of Germany and will spread eastward during the day. Given some QG forcing ahead of the approaching trough axis, models indicate cyclogenesis east of the frontal boundary and a surface low may form over central Germany during the day. Low-level convergence as well as low-level vertical wind shear is expected to overlap with high instability especially over southern Germany in the afternoon and evening hours. As DLS will be rather weak, thunderstorms along the cold front may be organized as clusters, but enhanced low-level vertical wind shear may be sufficient for more upright updrafts along the leading gust front over southern Germany. Models do indicate that a cold pool will form over southern Germany, and given strong low-level jets in the rear of the gust front, chance for severe wind gusts is expected to increase. Well-developed gust front may make its way into northern Austria and Czech Republic in the evening hours, where models also indicate strong low-level winds. Expect that wind gusts will exceed 25 m/s at numerous places, a level 2 is warranted. Isolated large hail is also not excluded given high instability and forcing, although weak vertical wind shear is a limiting factor.

Northern Germany

Along the cold front, convection is expected to spread eastward, where dry and well-mixed boundary-layer will be present. This will also lead to an attendant threat of dry downbursts, and isolated severe wind gusts are forecast. Convection will likely weaken in the evening hours due to decreasing instability, and storms are forecast to become more elevated.

North-western Italy region, south-eastern France

At the southern edge of the trough axis, upper jet stream ejects into north Mediterranean during the day. Given some QG forcing along the trough axis, convection may develop that will profit from increasing DLS, and isolated large hail is expected. However, forcing will be very limited and cap may be too strong for initiation. During the day, weak cold air advection will also limit low-level forcing, and thunderstorms may decease.

British Isles, northern France

Latest GFS and WRF indicate quite strong instability in the range of the trough axis due to daytime heating, and showers and thunderstorms are forecast to form. Given weak vertical wind shear, some spouts may form especially over Ireland during the day.

Northern Baltic States region

Upper cut-off low will provide strong DLS that will overlap with unstable air mass to the east. Along the frontal boundary expected to the north and east of the cut-of low, forcing will likely be strong enough for initiation. Supercells are not ruled out as SRH values are forecast to reach more than 100 J/kg in the lowest 3 km. Tornadoes are forecast to be most likely over western Russia, where low-level buoyancy will be strongest. Isolated large hail and severe wind gusts are not ruled out. Convective activity will likely weaken during the night hours.

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