Thunderstorms brings excessive rain to Europe



  • Valid: Tue 30 Jul 2019 06:00 to Wed 31 Jul 2019 06:00 UTC
    Issued: Mon 29 Jul 2019 22:40
    Forecaster: DAFIS

    A level 1 was issued for UK and N France mainly for severe convective wind gusts, excessive precipitation, and tornadoes.

    A level 1 was issued for Germany, Switzerland, Austria, and N Italy mainly for severe convective wind gusts and excessive precipitation.

    A level 1 was issued for Poland, Czech Republic, Slovakia, NE Hungary, N Romania, SW Belarus and Ukraine for excessive precipitation, large hail and severe wind gusts.

    A level 1 was issued for mountainous parts of Georgia and SW Russia mainly for large hail.

    photo: ESTOFEX;desc: Storm Forecast valid Tue 30 Jul 2019 06:00 - Wed 31 Jul 2019 06:00 UTC.;

    SYNOPSIS

    A deep low enters the English Channel (995 hPa at 21z, 29/07) bringing gale-force wind gusts to UK and France. The strong ridge which brought unseasonably warm air masses up north to the Arctic is gradually breaking over the North Sea in the presence of two troughs. An embedded short-wave trough over Scandinavia will cross the Baltic States and Eastern Europe enhancing the upper-level wind field by producing a jet stream which will overlap with unstable air masses below. A large part of Europe will experience either diurnally driven storms or forced by strong PVA. Some rare active storms will reach the SE coast of Iceland in the early morning of Tuesday 30/07.

    DISCUSSION

    UK and France

    The deep cyclone entering the English Channel is expected to shift NE crossing UK on Tuesday 30/07. Non-convective gale-force wind speeds will be the main threat but numerical models also show a high probability for storms which will also be able to produce severe wind gusts. Complex vertical wind profiles in the UK create low confidence for well-organized convection, but storms may produce short-lived tornadoes given the strong low-level shear.

    Germany, Switzerland, Austria, and N Italy

    In the Alps, storms will form early in the afternoon of Tuesday 30/07 and flash floods are possible. Strong synoptic lift late in the afternoon and night will result in DMC events and even though CAPE is calculated to stay below 1000 J/kg, the increasing wind speeds in mid/upper troposphere will result in the tilting of storms and storm-organization in multi-cells. Excessive precipitation will be the main threat, especially in Germany.

    Poland, Czech Republic, Slovakia, NE Hungary, N Romania, SW Belarus, and Ukraine

    A wide area with warm air masses, rich in moisture (Tds 18-20oC), is found in Eastern Europe, under the heart of the weakening ridge. A cold front is approaching from Russia and the Baltic States, and the boundary is expected to receive the most intense thunderstorms. NWP models show widespread CAPE values of 1000-2000 J/kg and locally enhanced DLS exceeding 10-15 m/s. The main threat will be excessive precipitation given more the 30-35 mm PWAT and slow storm motion vectors, but in South Poland and the Czech Republic more steep lapse rates increase also the probability of large hail.

    Georgia and SW Russia

    The jet stream extending from Greece towards the Caucasus will lead to strong DLS locally exceeding 25 m/s. Storms are expected to fire up in the mountains given the low-level cap elsewhere and the absence of synoptic lift. Storms will be able to produce large hail.



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