Storm Forecast
Valid: Thu 16 Sep 2010 06:00 to Fri 17 Sep 2010 06:00 UTC
Issued: Wed 15 Sep 2010 21:36
Forecaster: GATZEN

A level 1 was issued for Belarus and the surroundings mainly for tornadoes.

A level 1 was issued for south-western Iberia mainly for excessive rain.

SYNOPSIS

An intense trough is placed over Scandinavia. Several vort-maxima travel rapidly around its periphery. The most intense will cross Poland, Belarus, and western Russia during the period. Cold air has spread into most of Europe. A moist and slightly warmer air mass is expected over eastern Europe. Over the Mediterranean, two troughs are present over the western Iberian Peninsula and over the Aegean Sea. Warm air spreads into the west Mediterranean and Turkey to the east of both troughs. Colder air is present over Iberia and from the central Mediterranean Sea to the Aegean.

DISCUSSION

Belarus and surroundings

The intense short-wave trough will cross Belarus during the afternoon. An associated 40 m/s mid-level jet streak crosses southern Belarus and is associated with strong DCVA over the northern parts. This will lead to an ageostrophic low-level flow that helps to maintain a moist boundary-layer east of the trough axis and surface cold front. Dewpoints of 13°C are currently observed over Belarus and will likely be present during the period as well. On Thursday, QG forcing is expected and neutral lapse rates are likely. Given the moist boundary-layer and some diurnal heating, weak CAPE will likely develop in the noon and afternoon hours.

Although the surface trough is not well developed as indicated by latest models, some low-level convergence is likely. When sufficient instability is available this forcing will likely lead to showers and thunderstorms. These will rapidly organize in the strongly-sheared environment (10 /15 m/s 0-1/0-3km bulk shear) and are forecast to be capable of producing tornadoes as indicated by curved low-level forecast hodographs. Large hail is expected to be unlikely as instability is weak and convective clouds are expected to be rather shallow. Isolated severe wind gusts are also forecast. Storms will move north-eastwards and are forecast to weaken quickly in the evening hours.

Western Iberia

Iberia is affected by a mid-level trough that is present to the west. With southerly winds, a warm air mass originating from the Atlas mountains spreads into the west Mediterranean Sea. Farther west, a moist maritime air mass is advected into western Iberia. This air mass is slightly unstable in the range of the mid-level trough, and diurnal heating is forecast to lead to increasing instability. Showers and thunderstorms are forecast that will move north-eastwards with the moderately strong south-westerly flow. The main threat will be excessive rain along the south-western parts given the persistent convective activity and upslope flow. Rather strong vertical wind shear and favourably curved hodographs will also support mesocyclones capable of producing large hail and tornadoes.