Severe storms expected across E Ukraine, The Alps and S Scandinavia



  • Valid: Thu 05 Sep 2019 06:00 to Fri 06 Sep 2019 07:00 UTC
    Issued: Wed 04 Sep 2019 23:12
    Forecaster: GATZEN

    • A level 2 was issued across the southern Alps mainly for large hail and severe wind gusts.
    • A level 2 was issued for the northern Black Sea region mainly for large or very large hail and severe wind gusts and to lesser extent tornadoes excessive precipitation.

    photo:Estofex;desc:Severe Storms;

    Synopsis

    A mid-level trough has spread into north-west Europe. At its southern periphery, a vortex splits from the westerly’s and digs into the Ligurian Sea. The northern portions of the trough will lift across Scandinavia and the Baltic Sea. Downstream, mid-level vortices are located across the Ionian Sea and the northern Black Sea region.

    Discussion

    Southern Alps

    Ahead of the approaching mid-level trough, large-scale lift affects a moist and slightly unstable air mass. CIN is already weak and the potential of storms will increase during the day, also in response to diurnal heating. Storms are forecast to form over the Alps and will move towards the north-east. Long straight-line hodographs are in place ahead of the trough, promoting spitting storms and multicells. These will be capable of large hail and severe wind gusts. Storms may merge to a larger mesoscale convective system in the afternoon when frontogenetical forcing increases. This may cause a higher wind gust threat, before storms will become gradually elevated and spread east- and southward.

    Eastern Ukraine to northern Black Sea region

    Rich low-level moisture and steep mid-level lapse rates overlap near the center of a mid-level vortex. Warm air advection from the east will support some large-scale lift, and thunderstorms are likely along a warm front. Low-level hodographs indicate strong curvature and increasing length close to the Black Sea, where organized storms are most likely. With around 15 m/s deep layer vertical wind shear and 1000 J/kg mixed-layer CAPE, severe multicells and supercells are forecast, capable of large or very large hail and severe wind gusts.

    Additionally, excessive precipitation is forecast given moist profiles and relatively slow storm motion. Storms may even produce a tornado or two due to low cloud bases. Clusters of storms may merge along the warm front and may go on through-out the night.

    Southern Scandinavia

    Weak CAPE but deep layer shear of 15 to 20 m/s set an environment for potentially organized thunderstorms. A cold front will be associated with strong frontogenetical lift sufficient for convection initiation. Storms will quickly move north-eastward and may merge to a linear cluster along the cold front. Main threat of these storms will be some severe wind gusts.

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