Storm Forecast
Valid: Mon 16 Aug 2010 06:00 to Tue 17 Aug 2010 06:00 UTC
Issued: Sun 15 Aug 2010 22:14
Forecaster: DAHL

A level 2 was issued for E and central Poland ... Slovakia ... N Hungary for large hail, damaging winds, heavy rain, and tornadoes.

A level 1 surrounding the level 2 was issued for eastern central Europe for the entire facet of severe weather (see text for details).

A level 1 was issued across E Spain mainly for severe wind gusts and large hail.

A level 1 was issued for N and W Germany ... Denmark ... the Benelux countries mainly for severe rainfall.

SYNOPSIS

A large and rather intense upper cut-off low has settled over central Europe and will slowly begin to merge with an approaching
Atlantic upper upper trough late in the period. Perturbations at the periphery of the upper low maintain a compact SFC low which should stall over NW Germany/Benelux on Monday, undergoing slow weakening. A very moist and quite unstable air mass remains in place east of the upper low.

DISCUSSION

... eastern parts of central Europe ...

It seems that a rather complicated convective scenario will unfold on Monday, with potentially quite severe outcome. However, some uncetainties exist.

It seems that a very unstable air with MLCAPEs locally exceeding 3000 J/kg will be in place from E Hungary across E Slovakia into E Poland. Farther west, CAPEs will likely be weaker, probably ranging between 500 and 1000 J/kg.

The shear profiles will become quite impressive across W Hungary, W Slovakia, and central Poland ... i.e., west of the plume of most the unstable air.
Consequently, there seem to be three regimes ... i) rather weakly unstable but favorably sheared, ii) strongly unstable and weakly sheared, and iii) a small overlap of both regimes. The storm coverage in the strongly sheared westernmost regime is uncertain, with models offering both isolated cells and upscale growth into a large MCS.

This suggests that supercells and line segments capable of large hail, damaging winds, and possibly a few tornadoes may occur over W Hungary, W Slovakia and central Poland. Farther east, the mode should shift towards multicells which will primarily produce severe wind gusts and heavy rainfall, though some hail may also occur. Between these regimes, a "lucky" cell may profit from strong instability and strong shear, with fair chances of becoming an intense supercell capable of the entire facet of severe convective weather.

Which of these three regimes will dominate the convective scenario is uncertain at the moment.

... N and W Germany ... Denmark ... Benelux ... N France ...

Thunderstorms will likely persist in the wrap-around moisture across N/W Germany, Benelux, and N France. This activity will have the potential of supporting heavy convective rainfall. Over N Germany, a small overlap of instability with the 20 m/s 0-6 km bulk shear isotach is simulated, so that a marginally severe wind gusts and maybe some hail could occur.

... E Spain ...

Scattered thunderstorms will likely form over eastern Spain in the afternoon hours. 20 m/s DLS suggest that well-organized multicells and/or supercells may occur. Main threats are severe wind gusts and large hail.