A severe threat 2 has been issued for SE Germany mainly for severe wind gusts, large hail and excessive precipitation

A Severe Threat 1 had been issued for CRTL France and SW Germany and parts of Be-Ne-Lux mainly for large hail, excessive precipitation and to a lesser degree for severe wind gusts.

A Severe Threat 1 had been issued for parts of E Europe, mainly for excessive precipitation and large hail

On Monday an upper trough will slowly translate towards central Europe with increasingly upslope flow on its forward flank. QG and diabaticly-induced low level pressure falls reinforced by leeside cyclogenetic effects will lead to the formation of low pressure area from central France to S Germany. Within an potentially unstable airmass, organized DMC gets likely.
Additionally, locally severe convection will be possible alongside a weak cold front from E Poland to N Romania

…CRTL France to SW Germany…

Warm front north to the low pressure area will strengthen in response to WAA and differential heating. NWP guidance suggests initially elevated morning-convection may become surface based south to the warm front during noon/afternoon. Despite somewhat uncertain cloudiness within the warm sector, 800-1200 J ML CAPE is forecast between Paris and the Saarland. Given DLS of around 15 m/s, storms are expected to organize into multicells, with some mesocylonal structures possible with the 100-200 m2/s2 0-3 km helicity along the warm front. Main threat will be excessive precipitation due to training effects, but also a large hail events will be possible with any more confined updraft.

…S Germany…

Strong sfc heating will lead to temperatures between 25 and 30 °C over most parts of Bavaria and Baden-Württemberg. While a lag of sfc moisture is simulated close to the Alps as a result of Foehn, dew points around 15 °C are likely a little more to the North. Owed to Föhn induced EML, ML lapse will locally exceed 7 K, resulting in ML CAPE of 1000-2000 J/kg mainly across Bavaria. With increasing DCVA, CI is anticipated over Baden-Württemberg in the afternoon initially along medium mountain ranges like the Schwäbische Alb.
Backing low-level flow in combination with strengthening ML wind results in the generation of up to 300 m2/s2 0-3km helicity. With moderate DLS of 15-20 m/s, 1 or 2 supercells are possible especially if storm mode stays more discrete.
Later on, confidence is high that cold pool interaction with the 0-3km shear-vector will lead to the formation of a QLCS, as also suggested by nearly all mesoscale models. Such a system will rapidly propagate into Bavaria in the evening, producing swaths of severe wind gusts especially if low level inverted-V Föhn-profiles are also incorporated (most probable with a more southerly track of the system). Therefore a 15 % wind line has been introduced.
Besides severe wind gusts, a few hail events are also possible with the initial stage of the storms and generally over Bavaria, where wet-bulb-zero is lowest.

…E Europe…
Along an eastward moving cold front, DMC will develop withing the diurnal cycle. 1000 J/kg and DLS around 10 – 15 m/s will favor multicell capable of producing excessive precipitation and some hail events. Severe potential will move outward the forecast area during the evening.

Model consistency, additional remarks

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A severe Threat 2 has been issued for parts of Slovenia, extreme northern Croatia, southeastern Austria and western Slovakia mainly for extremely excessive precipitation, large hail and to a lesser degree for severe wind gusts.

A severe Threat 1 has been issued for parts of central Europe mainly for (extremely) excessive precipitation, large hail and/or hail accumulations.

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Model consistency, additional remarks

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A severe Threat 1 has been issued for parts of central Europe mainly for (extremely) excessive precipitation, large hail and/or hail accumulations.

A severe Threat 1 has been issued for parts of central France mainly for excessive precipitation, large hail and/or hail accumulations.

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Model consistency, additional remarks

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Update 1 for Convective Outlook for 2018-04-29

A severe Threat 1 has been issued for eastern France, SW Germany and parts of Be-Ne-Lux mainly for severe wind gusts, large hail, excessive precipitation and a tornado event

A severe Threat 1 has been issued for parts of eastern Germany mainly for excessive precipitation and an isolated large hail event

A Severe Threat 1 has been issued for North Italy, mainly for large hail, excessive precipitation and to a lesser degree for severe wind gusts

A lead upper level trough extends from the Norwegian Sea to western Iberia yielding a south-westerly flow pattern across central Europe. At lower levels, lee cylogenesis north to the Pyrenees creates a week surface low across southern France during the next hours. Coupling with the upper trough results in a baroclinic development. As the emerging low pressure system travels northeastward in a gradually destabilizing atmosphere, well organized convection is likely during Sunday afternoon and night.

…E France, Be-Ne-Lux, Germany…

Prefrontal CI is currently in progress south to Reims (Fr). This convection should organize into the expected linear MCS (see original Convective Outlook). Some further, more isolated cells may trigger in front of the approaching system somewhere along the french/belgian borderline.

Concerning the pre-storm environment, 12 UTC soundings confirm a relatively moist BL from E France to SW Germany (specific moistures > 10 g/kg), but mid-level lapse rates seem to be less steep than expected. In addition a lot of debris cloudiness can be observed within the warm sector by the help of satellite data. Although CAPE is still expected to increase up to locally 1000 J/kg, we downgraded to a high end Severe Threat 1. This is for the following reason:

As the lapse rates (and thus CAPE) are less steep than predicted, very strong cold pool organization gets unlikely. This reduces the chance for significant severe wind gusts. In addition, the lower instability does not justify a 15 % hail line anymore (which is necessary for a Severe Threat 2).

There are no significant changes upon the other thunderstorm/threat areas.

…N Italy…

Diurnal heating will lead to CAPE between 500 and 1000 J/kg within a moderate shear environment with veering hodographs (SRH exceeds up to 150 J/kg). In the late afternoon single and multicell convection will trigger along the Alps and somewhere on the Padan plain. The latter is somewhat uncertain but especially UKMO EURO 4 suggest a single supercell storm north of Parma. Overall severe potential satisfies a brief Severe Threat 1

…Parts of eastern Europe/Balkans…

Scattered disorganized storms will initiate within the diurnal cycle. Locally heavy precipitation will be the primary threat, followed by medium size hail. Activity will rapidly diminish after sunset.

Model consistency, additional remarks

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A Severe Threat 1 has been issued for parts of Central Europe (including Germany and Poland) mainly for severe wind gusts, large hail and excessive precipitation.

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Model consistency, additional remarks

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