Extended Forecast
Valid: Tue 04 Jun 2019 06:00 to Wed 05 Jun 2019 06:00 UTC
Issued: Sun 02 Jun 2019 07:28
Forecaster: GROENEMEIJER

A level 1 was issued across East Romania, Moldova and parts of South Ukraine, mainly for very heavy rainfall and large hail.

A level 1 was issued across parts of North France, Luxembourg, East Belgium, East Netherlands and Northwest Germany primarily for hail and tornadoes.

DISCUSSION

+++ note: the low probability thunder line has been omitted +++

East Romania, Moldova, South Ukraine...

A cut-off low over the southern Balkan peninsula is slowly moving northeastward during the day. Ahead of it, a southeasterly flow advects humid and unstable air into the area. A subtle vorticity maximum rotating around the low is expected to create modest upward vertical motion across the area during the day. 1500 and 2500 J/kg of weakly to uncapped CAPE is expected to build, widespread convection is expected to develop. As wind shear is weak to moderate, storm propagation should be slow and very high local accumulations of rain will be possible, creating a flash flood risk. Some large (2-5 cm) hail will also be possible as well as a modest risk of severe wind gusts. NWP guidance suggests that storms may gradually cluster.

North France, Luxembourg, East Belgium, East Netherlands and Northwest Germany...

A strong southwesterly mid-/upper-level flow is present across western Europe, that is associated with a front that represents the western edge of a warm and humid air-mass across East France and much of Germany. There is consensus among ECMWF, GFS and ICON-EU that a frontal wave is forecast to translate northeastward across France during the afternoon, reaching Northwest Germany by the evening. The wave is expected to provide lift that will result in scattered convective initiation near the front during the late afternoon as approximately 1000 - 1500 J/kg of mixed-layer CAPE will be available.

Relatively strong (~20 m/s) deep-layer shear, suggesting that a few supercells will form that should be capable of producing large (>2 cm), and possibly very large (> 5 cm) hail. Moreover, fairly large hodographs boasting 150-200 m2/s2 of 0-1 storm-relative helicity are expected ahead of the wave, with 0-1 km shear near 10 m/s, indicating that there is some risk of tornadoes as well.