CONVECTIVE FORECAST
VALID 06Z THU 10/06 - 06Z FRI 11/06 2004
ISSUED: 09/06 22:58Z
FORECASTER: DAHL

There is a slight risk of severe thunderstorms forecast across France ... S Benelux ... Germany ... S Poland ... the Chech Republic ... Slovakia ... Austria ... Hungaria.

General thunderstorms are forecast across the Iberian Peninsula ... central Europe ... SE Europe.

General thunderstorms are forecast across the NW British Isles.

SYNOPSIS

Strong SWLY upper flow has established over WRN parts of Europe ahead of Atlantic upper long-wave trough ... with downstream upper ridge cresting over central Europe. Over W Russia ... another upper trough is present ... progged to close off into a cut-off low on Thursday. This upper flow regime is slowly translating eastwards ... with the slightly decreasing amplitude. As the Atlantic trough reaches the British Isles late in the period ... kinematic profiles over western and central Europe will strengthen some. Plume of weakly ... locally moderately ... unstable air mass is curving from Iberia across France and Germany into the Balkan States with the main wavy low-level baroclinic zone aligned roughly parallel to the upper flow. Weak/extensive high pressure area will persist across southern Europe.

DISCUSSION

...slight-risk area...
Thermodynamic profiles within most of the theta-e plume are suffering from relatively weak mean lapse rates ... and predominant mixed-parcel mixing ratios of less than 10 g/kg. This has resulted in CAPEs in the 500 to 1000 J/kg range in the Wednesday afternoon/evening launches. However ... widespread cloudiness/convection has not allowed for homogenious boundary layer heating ... and produced various cold pools and precip ... so that large variations in BL moisture ... BL wind field and BL temperatures have been present ... with Wednesday's soundings being unlikely to have resolved the entire spectrum of variations that have been present.

GFS is offering CAPE in excess of 2000 J/kg over N France/S Benelux and over the N Balkan towards Thursday afternoon ... while MESO ETA advertises CAPEs in the 1000 to 1500 J/kg range ... which appears to represent the maximum CAPE values that will be present tomorrow somewhat better than GFS. Given widespread mid/upper cloudiness and convective debris ... average MLCAPEs may only range from 800 to 1000 J/kg on Thursday.

Kinematic setup will improve as upper flow increases over western and central Europe ... with 500 hPa flow in excess of 15 to 20 m/s overspreading the unstable air mass. GFS 12Z simulates 0-3 km SRH's of 100+ J/kg to be present roughly along the main 850 hPa theta-e gradient at the NRN edge of the theta-e plume ... possibly associated with regions of low-level WAA. However ... various outflow boundaries have been laid out by Wednesday and Wednesday night's convection ... and the low-level wind field will likely exhibit strong spatio-temporal variations ... aided by the complex terrain across much of the region ... probably promoting 0-3 km SRH's well in excess of 100 J/kg locally/temporally.

GFS and GME show various ... relatively small ... 300 hPa CVA maxima which cross the NRN parts of the theta-e plume during the day ... partly being accompanied by mesoscale SFC wave lows that move eastwards along the front ... which will be potential foci for convective development. Also ... small-scale BL features such as outflow boundaries ... and orographic forcing may prove instrumental in initiating TSTMS.

Altogether ... capping seems to be weak enough to expect relatively large TSTM coverage. Though large-scale setup is somewhat marginal ... anticipated variations of the kinematic/thermodynamic fields suggest that storm environments may locally be more than adequate for severe TSTMS. Main threat will be large hail and severe straight-line winds with /partly bowing/ multicellular storms. Also ... supercells may occur ... posing additional threat for a few tornadoes. If thermodynamic fields are stronger than currently anticipated ... an upgrade to MDT may be necessary on Thursday.

...N British Isles...
As upper cold pool associated with the Atlantic upper trough overspreads the N British Isles ... sufficiently deep convective mixing should occur to allow for a few TSTMS during peak-heating hours. Deep shear should be on the order of 15 to 20 m/s in the SRN portions of the TSTM area ... and a few brief marginally severe hail/wind events may occur. Weak thermodynamics precluding a SLGHT ATTM.

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