Storm Forecast
Valid: Fri 05 Sep 2014 06:00 to Sat 06 Sep 2014 06:00 UTC
Issued: Thu 04 Sep 2014 18:01
Forecaster: TUSCHY

A level 1 was issued for parts of the Balkan States, the Alps and SE Germany mainly for a few excessive rainfall events. An isolated tornado event is also possible.

The same for S/CNTRL Italy.

A level 1 was issued for NE Spain mainly for an isolated large hail and severe wind gust threat.

SYNOPSIS

Split flow / high-over-low pattern persists over Europe. An anticyclone is centered over Lithuania/Latvia and slides E/SE towards Belarus. A weakening cyclonic vortex hovers over the Adriatic Sea and another vortex can be found over NE France (although models differ if this one will be closed at all). A sharp trough north of Scotland chokes off the westerlies and drifts south as a closed cold-core low. A few non-severe thunderstorms fire within its vicinity.

DISCUSSION

Lowering thickness along the western and southern fringe of the high over Belarus atop a seasonable moist boundary layer with numerous weak mid-level disturbances cause a belt of enhanced shower and thunderstorm activity. This area runs from Benelux to Italy to the N-Aegean Sea. Weak steering flow supports slow moving storms with heavy rain and marginal hail. Effective PWs aoa 30 mm exist over the S Balkan States and that's where a rainfall level 1 was added. Mesoscale BL moisture pooling along convergence zones may increase chances for an isolated spout-type tornado event.

Same for SE-Germany and parts of the Alps, where another level 1 was issued.

Overnight convection is forecast west of Denmark over warm SSTs. Latest data keeps the main activity just offshore.

S/CNTRL Italy will be another area of concern. Slow moving storms could dump lots of rain in a short amount of time with local flash flood problems. Strong updrafts could also induce a few strong waterspout events along the coasts.

Overlap of moist marine air beneath steep mid-layer lapse rates is forecast over NE Spain as a thermal low over CNTRL Spain exhibits its diurnal intensification cycle. Easterly BL flow beneath 25-30 kt westerly flow at 500 hPa offer some directional shear, so an isolated better organized storm is possible. Large hail and localized downburst events are possible. We went a bit offshore with the level 1 to account for an evening cluster, which comes off the E-Pyrenees.