CONVECTIVE FORECAST
VALID Sun 17 Jul 10:00 - Mon 18 Jul 06:00 2005 (UTC)
ISSUED: 17 Jul 09:45 (UTC)
FORECASTER: DAHL

There is a slight risk of severe thunderstorms forecast across central France.

SYNOPSIS

Upper trough off the SW-European Atlantic coast will phase with vigorous N-Atlantic trough ... and reach the Iberian Peninsula and WRN France by early Monday morning. This will promote mid/upper ridging to spread into the central/northern Mediterranean regions. Not much of a change expected over ERN Europe ... with stationary broad upper longwave trough covering most of E Europe ... and a quasistationary upper cutoff cyclone over the Baltic Sea. Striking feature at low/mid levels is impressive mixed layer covering E Spain and the western Mediterranean Sea ... supporting potentially large CAPEs once sufficient BL moisture has accumulated beneath the mixed layer. However ... depth of low-level moisture across SW Europe is somewhat uncertain ATTM.

DISCUSSION

...France...
On Sunday 00Z ... edge of SW European EML plume has been present over SRN portions of France per radiosonde data. Numerical guidance is suggesting that this plume will be reinforced and spread across south and central France later today. Indications are that moisture will remain somewhat inhomogeneous ... but that locally about 13 - 14 g/kg mean mixing ratios will be realized ... which should support CAPEs on the order of 1000 to 1500 J/kg. Current thinking is that isolated TSTMS will form in the late afternoon hours over central and S France in region of weak pressure falls/low-level convergence. Storms may merge into larger clusters in the late evening hours ... and may be sustained through much of the night over N France where low-level WAA should be maximized. Shear profiles are expected to weaken over NRN France during the day ... and remain moderately strong over the south with 20 to 25 m/s. Low-level shear should remain quite meager though small-scale augmentations may occur. Current thinking is that a few severe TSTMS may develop ... especially towards the south of France ... with main threats being large hail and severe straight-line winds. The possible MCS over N France in the overnight hours should not exist in particularly impressive kinematic environment ... and severe threat should be limited ... though an isolated marginally severe hail/wind event could occur.

Kinematic and thermodynamic profiles will also be favorable for severe TSTMS farther E across N Italy ... but indications are that air mass will become increasingly capped courtesy of mid-level warm advection and subsidence in association with mid/upper ridging.

...N UK...
Latest GFS runs are coming up with weak CAPE across the NRN UK ahead of the cold front/trough. 00Z ascents from within the prefrontal air mass do not show any convective potential ... and main DCVA-forced UVV's - acting to destabilize the atmosphere - will not arrive until early Monday morning. Current thinking is that convective activity across the UK will be insignificant through this period ... though situation will be monitored for potential destabilization.

...Balkans...
Vort maxima at the periphery of the mean E-European long-wave trough should again support widespread TSTM development in weakly capped air mass. About 15 m/s deep shear ... rather deep CBLs and about 1000 J/kg CAPE should be common by afternoon ... being supportive of isolated hail/wind events ... possibly approaching ... or briefly exceeding ... severe levels.

...Eastern Europe and Scandinavia...
Weak low-level shear ... low LCL's and weak/no CINH ... and low-level buoyancy suggest that any misoscale vertical vorticity may be concentrated into a tornado in the time scale of a single convective updraft. Though sources of misovortices cannot be identified for such a large area with such a sparse observation network ... a few non-mesocyclonic tornadoes could occur. Threat is insufficient for a categorical outlook though.

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