Large Hail, Severe Wind Gusts and Tornado Warning Issued for France and Belgium



  • Valid: Tue 18 Jun 2019 06:00 to Wed 19 Jun 2019 06:00 UTC
    Issued: Mon 17 Jun 2019 21:42
    Forecaster: DAFIS

    A level 2 was issued for parts of France and Belgium for large hail, severe wind gusts and tornadoes.

    A level 1 was issued for France, Belgium and Luxemburg mainly for large hail and severe convective wind gusts.

    A level 1 was issued for parts of the Netherlands, Germany, Denmark, and Sweden for large hail, excessive precipitation and severe convective wind gusts.

    A broad level 1 was issued for the Balkans, S Austria, S Switzerland and N Italy mainly for large hail and excessive precipitation.

    A level 1 was issued for Turkey mainly for large hail and excessive precipitation.

    A level 1 was issued for parts of Finland, Sweden and W Russia for severe convective wind gusts.

    photo:ESTOFEX;link: http://www.estofex.org;desc: Storm forecast valid Tue 18 Jun 2019 06:00 - Wed 19 Jun 2019 06:00 UTC.;

    SYNOPSIS

    A high-pressure system over Poland limits convection in a large part of E Europe, but more to the south, in the Balkans, the environment continues to be conducive for diurnally driven thunderstorms. In W Europe, a trough is found in NE Atlantic with several short-wave impulses in its periphery, one of them is expected to cross Scandinavia and move over the northern flank of the ridge towards Russia, reducing the geopotential and increasing the mid-level flow as a strong temperature gradient is building up.

    Another short-wave trough is expected in the late afternoon of Tuesday 18/06 coming from the Atlantic and its track will cross N France and Benelux, providing a strong lift to unstable air masses. In fact, this area is expected to receive the most intense thunderstorms, also due to the Spanish plume that brings steep mid-level lapse rates.

    In the Mediterranean, a ridge is intensifying with an axis from Algeria towards Italy and will suppress any convection in the Iberian Peninsula, Sardinia, Corsica and N Africa. On the other hand, the continental parts of Italy, the Balkans, Turkey and Cyprus will experience locally strong thunderstorms due to the abundant moisture close to the surface and steep mid-level lapse rates.

    DISCUSSION

    France and Belgium

    The latest model output of GFS model (12z - 17/06) shows an overestimation of dewpoints over France, with the most pronounced differences with the observations in Central and SW France. A more realistic analysis from the IFS model shows 12-14ºC dewpoints. This differences apparently have an impact on CI in the forecast fields, as GFS produces less CIN than IFS. Following the latter model, we expect thunderstorms in France to initiate late in the afternoon as the approaching vigorous short-wave trough from the west will provide the necessary additional lift.
    Any storm that will form inside the level-2 area will be able to become quickly a supercell due to the strongly sheared and helical environment. IFS forecasts more than 1500 J/kg MLCAPE overlapping with 15-20 m/s DLS and comparable 0-3km bulk shear, with more than 150-200 m2/s2 SREH0-3km. This environment will be ideal for thunderstorms to produce large to very large hail and severe wind gusts. Moreover, strong low-level shear and veering winds create looped forecasting hodographs with nearly 100 m2/s2 SREH0-1km and adding the low LCLs in all available NWP models, tornadoes cannot be ruled out, but this will depend on the convective mode. AROME model (12z run) shows a QLCS in N France, but also some discrete supercells which may produce tornadoes.

    rest of France, Belgium, Luxemburg, the Netherlands and Germany

    Very steep mid-level lapse rates create fat CAPE profiles and NWP models forecast excessive CAPE, mostly over France, with values exceeding locally 2000 J/kg. Storms will be able to produce large hail, more than 2-3 cm in diameter and severe wind gusts. In particular, vertical thermodynamic profiles over Germany, S Belgium and E-NE France show mid-level dry slots and high LCLs, increasing the probability of severe convective gusts at the surface, as strong evaporation cooling of downdrafts may accelarate them to high speeds.

    Denmark, Sweden, Finland and W Russia

    Denmark and S Sweden will be under the right exit of a mid-level jet stream, where a strong lift is expected and pre-existing unstable air masses will form thunderstorms which may cluster in a few MCSs. DLS will fluctuate between 10-20 m/s, but CAPE does not seem very impressive, reaching only locally 400-500 J/kg. A level 1 was issued mainly for severe convective wind gusts (and maybe a landspout given the strong LLS and low LCLs), as well as for large hail if an MCS form.

    In N Sweden, Finland and W Russia the environment is not much different but mid-level lapse rates are higher. Local severe wind gusts are also expected.

    Balkans, N Italy, S Switzerland, S Austria and Turkey

    A broad level-1 area was issued for a large part of SE Europe due to the abundant instability with very steep lapse rates and high PWAT. Storms should initiate in the late morning as the unstable masses near the surface are weakly-capped and slow storm motions are expected to keep diurnally-driven thunderstorms almost stationary, or at least with slow propagation speeds, producing excessive precipitation. In addition, large hail is well possible due to steep lapse rates and high cloud bases.


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