Storm Forecast
Valid: Thu 28 Oct 2010 06:00 to Fri 29 Oct 2010 06:00 UTC
Issued: Wed 27 Oct 2010 17:52
Forecaster: GATZEN

A level 1 was issued for southern Turkey mainly for excessive rain.

SYNOPSIS

A ridge over south-western Europe amplifies on Thursday. Downstream, two troughs migrate eastwards. The northern trough crosses Scandinavia and the Baltic Sea. The southern trough slows down over western Turkey. The boundary layer airmass is dry over a region from the Iberian Peninsula across the north Mediterranean and the Alpine region into eastern Europe. This dry air is also advected into the central and southern Mediterranean with northerly low-level winds in the wake of a cold front that moves eastward to the south of Turkey. A tongue of moist low-level air is present ahead of this front. Another tongue of moist maritime air is situated from the Bay of Biscay to the southern Baltic Sea along a frontal boundary. Steep lapse rates originating from northern Africa are expected over the east Mediterranean. Additionally, rather good lapse rates are forecast near the trough centres where cold mid-level air masses are present.

DISCUSSION

Turkey

A mid-level cut-off low moves slowly eastward and enters Turkey in the morning hours. A negatively-tilted short-wave trough will affect the western Turkey until noon. At low levels, a cold front moves eastward. Strong low-level convergence is forecast that will result in quite strong lift. The affected airmass is characterized by a moist boundary-layer as indicated by latest soundings. The steep lapse rates over the east Mediterranean are forecast to decrease near the front, but some CAPE will likely be available.

Current thinking is that a cluster of storms will continue to affect the south-western Turkish coast in the morning hours. The strong deep-layer vertical wind shear will support back-building storms. Upslope flow, strong low-level lift, and the rich boundary-layer moisture are expected to raise the potential of excessive rain. The threat of large hail is expected to be rather marginal as the storms will likely cluster. Isolated tornadoes are not ruled out along the leading cold front where the low-level vertical wind shear will overlap with weak positive low-level buoyancy.

Later in the period, cool low-level air masses will spread eastwards in the wake of the short-wave trough, and storms are forecast to weaken. Farther west, showers and thunderstorms near the trough centre are forecast to be mostly non-severe as the vertical wind shear will not support organized convection.

North Sea

A narrow cold-frontal rain band is forecast to develop over the southern North Sea and enters Denmark in the morning hours. Latest models indicate weak instability given a tongue of moist low-level air present over the southern North Sea. Mid-levels are forecast to cool to the north of a westerly jet streak that enters Denmark and the southern Baltic Sea. This will result in equilibrium level temperatures below -30°C for the most unstable parcel as indicated by the latest GFS model run.

Some thunder is forecast along the narrow cold-frontal rain band over Denmark. Marginally hail may be possible. A tornado is not ruled out along the leading gust front as low-level vertical wind shear is expected to veer. However, the weak low-level buoyancy will limit this potential. Farther east, decreasing low-level moisture will limit the potential of thunderstorms.