Storm Forecast
Valid: Wed 01 Apr 2015 06:00 to Thu 02 Apr 2015 06:00 UTC
Issued: Wed 01 Apr 2015 01:42
Forecaster: PUCIK

A level 1 was issued for parts of BENELUX, Germany, Austria, W Poland, Czech Republic, W Slovakia, Hungary and W Romania mainly for severe wind gusts and to the lesser degree for tornadoes.

A level 1 was issued for Ukraine to E Belarus mainly for severe wind gusts and to the lesser degree for tornadoes.

SYNOPSIS

An outbreak of arctic maritime airmass is ongoing over much of western and central Europe in the wake of the large trough. Prevailing northwesterly flow will overspread a belt from the Atlantic towards northern Balkans. In this belt, unstable conditions will prevail with scattered to widespread low topped showers and thunderstorms. Also thanks to the strong pressure gradient between a high centered over the Atlantic and a low centered over the Baltic states, strong background flow with widespread gusts over 20 m/s and isolated gusts over 25 m/s is forecast.

DISCUSSION

... BENELUX, Germany towards Hungary ...

12 UTC Tuesday soundings from Lerwick and Torshavn document well the arctic airmass which will advect over the whole region. In the 800 to 600 hPa layer, lapse rates of 7.5 to 8 K/km are forecast, close to wet-adiabatic due to the limited amount of low-level moisture. As soon as the daytime heating commences, quick destabilisation will result in few tens to few hundreds J/kg of MLCAPE. With virtually no CIN, uncapped parcels will quickly result in scattered to widespread DMC. The highest chance of thunderstorms will be present over eastern half of Germany, Poland and western Czech Republic.

Largely unidirectional shear profiles are forecast, with most of the shear confined to the lowest 1-2 km as 850 hPa flow stays around 20 m/s. An exception will be W to central Germany and BENELUX, where 20 to 35 m/s of DLS is forecast. Here, a higher chance of sustained supercells will exist, increasing the probability of tornado occurrence.

In the whole area, fast moving, low-topped DMC is forecast, capable of severe wind gusts, especially if clusters organize into linear segments. Hail may be common with any shower or thunderstorm, but limited moisture and low CAPE will likely preclude. In case that updrafts will be able to utilize the high degree of LLS, tornadoes may occur as well. As mentioned above, they are more probable over the western part of area, where stronger DLS will exist.

A large Lvl 1 is introduced, with lack of concentrated lift limiting the threat of widespread severe wind producing squall line and thus precluding Lvl 2.

... Ukraine towards Belarus ...

A plume of steep lapse rates is forecast to wrap around the occluding low, also covering this region. With situation similar to the other Lvl 1 area, environment characterised by marginal CAPE along with strong LLS will pose a risk of severe wind gusts and perhaps a tornado in case that supercells form. A limiting issue may be that higher DLS values will overlap with marginal CAPE only in the narrow belt.