CONVECTIVE FORECAST
VALID 06Z SAT 29/05 - 06Z SUN 30/05 2004
ISSUED: 28/05 19:35Z
FORECASTER: DAHL
General thunderstorms are forecast across the Iberian Peninsula.
General thunderstorms are forecast across the north-central Mediterranean and eastern Europe.
SYNOPSIS
Southern portions of extensive Atlantic upper low are progged to affect the Iberian Peninsula and France late Saturday evening/night. Downstream ... upper ridge will stretch from western France across the North Sea into the NE Atlantic on Saturday 06Z ... with its southern parts moving eastwards into central Europe by Sunday 06Z. Upper low over Scandinavia is progged make only little southeastward progress during the period ... and a weak upper low is expected to persist over the north-central Mediterranean and the Balkan states ... with weak disturbances present at its periphery. At low levels ... ahead of the Atlantic upper trough ... plume of subtropical/Atlantic moisture will spread across much of Iberia and western France during the period. Otherwise ... large-scale setup will not undergo much of a change owing to weak large-scale low-level flow.
DISCUSSION
...Iberian Peninsula...
West-Iberian 12Z launches indicate deep/rich moisture relative to locations farther east ... possibly owing to the advent of subtropical air. There is no indication of significant warming at mid-levels ... and air mass should destabilize with insolation until about mid day ... resulting in MLCAPEs in the 500 to 1000 J/kg range and weak CINH. Weak mid-level ridging may initially suppress initiation ... but as DCVA regime overspreads the region late in the day ... widespread TSTMS should develop. Current thinking is that TSTMS may struggle to form in somewhat drier environment and less favorable positioning beneath weak mid/upper ridge over E Spain ... with increasing chances of TSTM development towards the west. Peak activity will likely occur after about 19Z along the W edge of the 850 hPa theta-e plume ... and spread into central Iberia during Saturday night. Large-scale shear will be quite meager ... but local ... mainly orographic ... modifications of the low-level shear profiles ... may favor an isolated rotating updraft or two with an attendant threat for large hail. Allover severe threat should be too low for a SLGT.
...Italy...
Storms will likely form again over Italy ... and the Balkan States in the vicinity of the upper low. Exact positioning of weak vort maxima at its periphery is somewhat uncertain ATTM. Given this uncertainty ... will include all of Italy in a TSTM outlook though GFS' position of upper vort max would suggest TSTMS only over the south of Italy.
...Balkan States...
Over the Balkans ... ongoing weak low-level dry advection may weaken thermodynamic profiles some ... nonetheless ... TSTMS should form again aided by upslope flow and regions of weak ascent at the E periphery of the upper low. An isolated severe TSTM event cannot be excluded if cells favorably interact with orography and/or outflow boundaries or other small-scale BL features ... but resulting severe TSTM probabilities are too low for a SLGT.
...Central Sweden...
Scattered showers with a few TSTMS may form beneath upper low over central Sweden ... Indications are that low-level air mass will be too cold/dry for convection deep enough to allow for large TSTM coverage ... and a TSTM outlook is not warranted ATTM.
...Finland ... Baltic States ... Belarus...
Upstream ... somewhat stronger thermodynamic profiles ... i.e. nearly neutral with ELs at around 400 hPa ... are present ... and insolation along with DCVA-related forcing for UVVs will likely promote development of scattered TSTMS again. The stronger cells may produce small hail given low WBZ heights ... but severe TSTMS are unlikely. Chance of stronger storms will likely increase towards the S over Belarus into W Russia given more CAPE ... but chance of severe remains below SLGT criteria.
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