CONVECTIVE FORECAST
VALID Mon 18 Jul 06:00 - Tue 19 Jul 06:00 2005 (UTC)
ISSUED: 17 Jul 21:55 (UTC)
FORECASTER: GROENEMEIJER

There is a moderate risk of severe thunderstorms forecast across eastern France, Switzerland, northern Italy, southern Germany and western Austria

There is a slight risk of severe thunderstorms forecast across the moderate risk area including central Germany, parts of central and southern France, a larger part of northern Italy, Austria and a part of the Czech Republic

SYNOPSIS

Monday at 06Z a southwesterly jet streak ahead of a mid/upper- trough moves eastward over the western Mediterranean and the southeastern France. Ahead of the trough, a cold front replaces the deep elevated mixed layer with an originally polar air-mass. further northeast a near0stationary low-pressure system is located over the Baltic Sea.

DISCUSSION

...Alpine area...
Forcing for upward motion is expected to increase across southeastern France during the moring and affect areas to the east later on. Around 1000 J/kg of MLCAPE is expected to develop where strong solar heating occurs. During early afternoon storms are expected to initiate across eastern France...apart from storms tapping elevated instability that may already bw in place. Additional storms are expected to form over much of Switzerland, northwestern Italy, southern Germany and also across northeastern Italy later on.

30 m/s of deep-layer wind shear is expected to be present over southeastern France and Italy, and slightly lower values further north. As a result, storms may quickly develop into supercells, yielding a threat of large hail, strong downbursts and perhaps a tornado. Some threat of stronger tornadoes is expected across northern Italy and extreme southeastern France, where about 200 m2/s2 of storm-relative helicity is forecast and low-level shear should be the strongest.

Strong forcing suggests that large storm clusters are likely to form that probably turn into bowing MCS's moving eastnortheastward across northern Italy, and across Switzerland and southern Germany. Given steep low-level lapse rates ahead of the systems, quite some potential for damaging winds will be available. During the evening and overnight, parts of the Czech Republic, Austria and western Hungary could be affected by the storms as well.

...far northeastern France, eastern Belgium, Luxembourg and central and northern Germany ...
Lesser forcing is expected across far northeastern France, eastern Belgium, Luxembourg and central and northern Germany resulting in a lower storm coverage and less clustering than further south. However, the forecast ~20 m/s of deep-layer shear and 500-1000 J/kg MLCAPE appears sufficient for a couple of organized storms, possibly including a couple of supercells, that yield some threat of large hail and local severe winds.

...central Finland ...
500-1000 J/kg of poorly-capped MLCAPE will likely become available north of a diffuse and stalled frontal boundary across southern Finland. Surface-based storms will likely initiate again during the early afternoon. Given that around 10-15 m/s deep-layer shear in place, some well-organized multicells may form, that when back-building become rather slow-moving, so that high local rainfall accumulations may result. Additionally, some marginally large hail and gusty winds appear possible.

...Baltic Sea, southeastern Sweden, western Baltic States...
Some chance of (water)spouts is forecast across these areas in the neighbourhood of a vertically-stacked low pressure system that has soundings associated with it showing large low-level bouyancy and provides ample vertical vorticity.

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