Storm Forecast

Storm Forecast
Valid: Mon 11 Jun 2012 11:00 to Tue 12 Jun 2012 06:00 UTC
Issued: Mon 11 Jun 2012 11:05
Forecaster: GATZEN

A level 2 was issued for eastern Belarus and western Russia mainly for severe wind gusts, tornadoes, and large hail.

A level 2 was issued for western Belarus and western Ukraine mainly for excessive precipitation.

A level 1 was issued from the central Balkans into western Ukraine mainly for large hail.

A level 1 was issued for southern France mainly for severe wind gusts.

A level 1 was issued for north-western Spain and northern Italy mainly for large hail.


A broad and deep trough is placed over northern and western Europe. A very strong jet stream curves around the troughs base across the Iberian Peninsula and the west Mediterranean Sea. An intense vort-max will travel into France with the strong mid-level flow today. Ahead of the long-wave trough, a well-developed frontal boundary with embedded frontal waves will affect eastern Europe.


Western Ukraine to eastern Belarus and western Russia

Ahead of the European trough, a short-wave trough moves northward across eastern Europe. At 09 UTC, a frontal boundary extending from western Ukraine to the eastern Baltic States formed a frontal wave centered over the western Ukraine. It will move northward during the afternoon and provides strong QG forcing. Latest models indicate that a low-level jet currently over Belarus will spread into western Russia, where the warm front will progress northward.

Latest soundings indicate the presence of a deeply mixed elevated air mass across a broad region of eastern Europe. The boundary layer is characterized by rather rich low-level moisture especially along the frontal boundary from western Russia to western Ukraine and further into the central Balkans. Latest satellite images show clear regions from the western Ukraine to Belarus, while thunderstorms have developed near the frontal wave across north-western Romania and south-western Ukraine as well as along the nose of warm air across the northern Baltic States.

Along the frontal boundary, moderate to strong instability release is expected during the next hours. The current MCS is forecast to move north-eastward into the Ukraine and southern Belarus. The system will be affected by moderate vertical wind shear. At the leading edge of the gust front, severe wind gusts are forecast due to the strong winds at 700 hPa. The main threat will be excessive precipitation given the propagation nearly parallel to the frontal boundary and the strong forcing. Large hail and a tornado are not ruled out.

Further north, additional storms are forecast to develop in the broad warm air advection regime from eastern Belarus to western Russia. During the following hours, initiation of new cells near the warm front is expected. Coverage of storms will increase ahead of the approaching trough axis. The strong vertical wind shear at low to mid levels and favorably veering profiles will allow rapidly organizing storms. Supercells are forecast capable of producing large hail and tornadoes. Severe wind gusts are not ruled out. In the evening hours, the threat of severe wind gusts may increase as the MSC moves into eastern Belarus, where it may merge with more isolated cells. During the night, convection will weaken, but storms can go on along the leading frontal boundary well through-out the night.

Central Balkans

The delta of the strong Mediterranean jet stream will enter the Adriatic Sea during the afternoon hours. QG forcing can be expected across the central and northern Balkans due to DCVA and warm air advection.

The affected air mass is characterized by steep mid-level lapse rates over the central and southern Balkans, while rich low-level moisture is only indicated along the frontal boundary over the central Balkans. Current thinking is that storms will develop in the afternoon hours due to upslope flow over the mountains. Storms will organize given strong deep layer vertical wind shear that will increase in the evening hours. Supercells are forecast capable of producing large hail. Severe wind gusts and a tornado are not ruled out. Storms are expected to decay during the night.

Southern France and north-western Spain to northern Italy

In the wake of the frontal boundary, a moist adiabatically mixed maritime air mass is advected into southern France. Across northern Italy, lift at the cyclonically-shear flank of the mid-level jet will provide QF forcing and steepening lapse rates are forecast. The boundary-layer moisture is rather rich and will allow for CAPE in response to diurnal heating.

Showers and thunderstorms are forecast during the day over abroad region of France into northern Italy. The threat of organized storms is expected to increase in the southern portions of the area given rather strong deep layer vertical wind shear. Fast propagating cells will pose a threat of severe wind gusts especially over southern France, where a low-level jet will evolve during the afternoon. The strong low-level vertical wind shear poses also a threat of tornadoes, but rather weak low-level moisture seems to limit this threat.

Over northern Italy and north-western Spain, storms that form will profit from strong deep-layer shear. Supercells and multicells are forecast with large hail the main threat. Severe wind gusts are not ruled out. This convection may go on well into the night across northern Italy given the forcing ahead of the new trough axis entering the region from the west. Excessive precipitation is therefore not ruled out.

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