CONVECTIVE FORECAST
VALID 06Z SUN 28/03 - 06Z MON 29/03 2004
ISSUED: 27/03 21:56Z
FORECASTER: DAHL

General thunderstorms are forecast across the S Iberian Peninsula ... the SW Mediterranean Sea and S Italy.

SYNOPSIS

Potential Foci for convective development this period will be WAA regime over the SW and S-central Mediterranean ahead of deepening SFC low downstream from the eastward accelerating upper cut-off low W of the Iberian Atlantic coast ... and downstream vort max which will cross Greece ... the Aegean and W Turkey late in the period. Otherwise ... large SFC high pressure area lingers over wide parts of Europe ... NRN-stream short-wave troughs will affect the British Isles and Scandinavia ... but involved air masses are expected to be too stable to allow for significant convective potential.

DISCUSSION

...SW Mediterranean...
As cyclogenesis sets in over the SW Mediterranean early in the day ... SFC flow will veer to ELY directions across the S Mediterranean. Saturday's LICT and LIEE radiosonde ascents suggest modest increase in the low-level moisture. Indications are that this moisture will continue to increase during the day ... with dewpoints possibly climbing into the 10 to 13°C range. As this air mass is overspread by EML plume from the Sahara ... weak CAPE is advertised to develop by GFS. 60630 (Algeria) Saturday 12Z ascent may be representative of the air mass atop the S-Mediterranean BL on Sunday evening ... modified it does not reveal much CAPE ... and a formidable capping inversion. Nonetheless ... high-based TSTMS will likely form again over the Atlas ... and may advect into the S-central Med ... where low-level WAA may help sustaining the convection. Chances that storms root down into the boundary layer are rather low given low theta-e's/cool water surface temperatures. Shear in the cloud-bearing layer will likely be on the order of 30 knots ... and given steep lapse rates/dry mid-levels ... storms may produce strong downdrafts and some hail. Wind threat will likely be limited by stable SFC-based layer. TSTMS may merge into larger elevated clusters late in the period.

...SW Spain ... S Portugal...
Beneath the upper cold pool accompanying the the cut-off low ... scattered TSTMS should continue over the Ocean ... and spread into SW Iberia with daytime heating. It appears that NW edge of moderately strong 500 hPa flow may overlap with parts of this activity ... and a few marginally severe wind/hail events may occur especially over S-central Spain.

...Greece ... Aegean ... W Turkey...
At least two negatives exist for the Aegean region ... sustained lack of low-level moisture ... and UVV's crossing the region well N of where chances for weak instability exists. Hence ... confidence in TSTM development is quite low ATTM.

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