Storm Forecast
Valid: Wed 13 Apr 2016 06:00 to Thu 14 Apr 2016 06:00 UTC
Issued: Tue 12 Apr 2016 21:16
Forecaster: PUCIK

A level 1 was issued for eastern France mainly for large hail.

A level 1 was issued for southeastern Germany and northwestern Austria mainly for large hail and excessive precipitation.


SYNOPSIS

Situation will be dominated by an extensive cyclonic vortex centered over the Atlantic, with a southwesterly jet-stream stretching from its southern base towards Italy and Balkans area. Vortex is connected with another one over northern Scandinavia. In between, over much of western and central Europe, low geopotential heights are observed. In the prevailing westerly to southwesterly flow, several short-wave troughs will propagate from the main cyclonic vortex. At the same time, a ridge is observed over the southeastern Mediterranean.

Abundant DMC activity is forecast over Europe, especially in conjuction with the presence of lower temperatures at mid-troposphere and thus steeper lapse rates. Low-level moisture is still relatively poor, with dewpoints mostly below 10 deg C. Thus, marginal CAPE values are forecast at best. Nevertheless, some areas will see an overlap of instability with moderate to strong DLS and thus deserve a closer look.


DISCUSSION

... Eastern France ...

A shallow trough at mid-troposphere is forecast to approach the region towards 15 UTC. It is possible that abundant precipitation will be present in the morning and noon hours, likely giving way to some sunshine before 12 UTC. Thanks to the lapse rates around 7 K/km, CAPE on the order of few hundreds J/kg will be realised into scattered showers and thunderstorms. With 500 hPa flow around 15 m/s, 15 to 20 m/s of bulk DLS are forecast by most of NWP. In such conditions, multicells or even one or two short-lived supercells are likely. Main threat will be marginally large hail, also owing to the quite low height of 0 deg C isotherm.

... Southeastern Germany to Northwestern Austria ...

With the approach of trough at lower troposphere and a WAA regime, NWP simulates abundant precipitation ahead of the cold front that will pass the region in the evening hours. Models are in strong disagreement regarding the presence (or absence) of the latent instability, due to the lack of abundant low-level moisture. The highest chance for some isolated severe storms will be just north of the Alpine range, where strong DLS is forecast (above 20 m/s). In case that an isolated supercell manages to form, isolated large hail events will be possible. However, it is likely that convection will quickly cluster with an attendant threat of local excessive precipitation.

... Northern Italy ...

Strong DLS will be observed also over this region, but models disagree on the degree of initiation outside of the Alpine range. It is likely that some DMC will form especially towards the evening hours, but chances of severe seem too low to warrant a Lvl 1 atm.

... Belarus to Ukraine ...

Scattered to widespread coverage of showers and tstms is forecast over the region under the mid-tropospheric trough and cold mid-tropospheric temperatures. Despite weak DLS (mostly below 10 m/s), thunderstorms may form multicell clusters, stronger of which will be capable of large amounts of small hail, or possibly even marginally large hail. Coverage of such events should not warrant a Lvl 1.