CONVECTIVE FORECAST
VALID 06Z THU 19/08 - 06Z FRI 20/08 2004
ISSUED: 18/08 20:11Z
FORECASTER: GATZEN

There is a slight risk of severe thunderstorms forecast across southeastern France, northern Italy, Alpine region, southern Germany, Austria, Czech Republic, central Poland, Baltic states

There is a slight risk of severe thunderstorms forecast across northern France, southern Benelux, northwestern Germany

General thunderstorms are forecast across western and central Europe, southwestern Russia, Black Sea, southern Ukraine

SYNOPSIS

Intense upper long-wave trough present over western Europe, while North-African upper high ridges into eastern Europe ... yielding a deep very strong southwesterly flow from Iberian Peninsula to Central Europe and further to eastern Scandinavia. Several embedded vort-maxima are analyzed that move NE-ward. At lower levels ... warm airmass is expected southeast of a cold front from central Spain to eastern France, and northern Poland on Thursday, 12Z.

DISCUSSION

...Southern France, northern Italy, Alpine region, southern Germany, Austria, Czech Republic, Poland, Baltic states ...
Southeast of the frontal zone ... warm airmass is expected to destabilize due to diurnal heating. Latest soundings show steep lapse rates yielding CAPE of several hundred J/kg. Aloft ... very strong upper jet will lead to QG UVM as upper long-wave trough expands SE-ward. Expect that convection will form along and SE of the frontal boundary. Strong deep layer wind shear will be adequate for mesocyclones. Large hail and severe wind gust will be possible with any supercell that forms. As low-level wind shear will be relatively weak ... tornado potential is limited ... however ... locally low LCL heights and enhanced SRH due to orography and/or outflow boundaries will lead to enhanced tornado potential. Focus of severe activity is not clear today ... it is expected that strongest forcing/instability will be present from the western Alps/northern Italy to central Poland ... where upper short-wave is expected. A MCS or two may develop over this region. Severe wind gusts should be the main threat if MCSs will form. Over the Baltic states/northern Poland ... another focus of severe convection is forecast due to strong DCVA at the nose of the upper jet streak.

...Northwestern Europe ...
At the cyclonic flank of the upper jet streak ... several vort-maxima are expected to move NE-ward ... At lower levels ... convectively mixed airmass as indicated by latest soundings is present that will destabilize during the day. Although deep layer wind shear will decrease in the range of the trough axis ... relatively strong low-level wind shear is expected over the region. Underneath of mentioned vort-maxima ... thunderstorms should form ... that will likely organize into small bows/ mesocyclones due to rather strong vertical wind shear ... capable of producing strong wind gusts and isolated large hail/a few tornadoes. Best potential seems to materialize over northern France, Benelux, and NWrn Germany, where tornadoes will be most likely. It is not ruled out that several tornadoes may form including one or two strong tornadoes. Isolated large hail and severe wind gusts are also forecast.

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