CONVECTIVE FORECAST
VALID 06Z SAT 24/04 - 06Z SUN 25/04 2004
ISSUED: 23/04 21:57Z
FORECASTER: DAHL

General thunderstorms are forecast across the central Mediterranean and the the W Balkan States.

SYNOPSIS

Upper ridge is progged to bild over western portion of Europe ... while SEWD progressing short-wave trough over east-central Europe is closing off into an upper cut-off low early in the day ... stalling over the eastern Alps during Saturday afternoon. Upper low over the western Mediterranean ... will continue east ... and merge with the central European upper low towards Sunday early morning. At low levels ... high pressure will dominate the western parts of Europe ... weak low-pressure system will accompany Mediterranean upper low.

DISCUSSION

...N Italy ... N and W Balkan States...
Southward progression of low level polar air mass associated with central Eurpean upper low ... will initially be blocked by the Alps ... and removal of the warm air mass S of the Alps will occur from the NE late on Saturday. QG forcing for upward vertical motion ahead of the upper feature will overspread N Italy and the N Balkan States during the day ... which will aid TSTM initiation along the SWWS progressing SFC frontal boundary ... and ahead of the SFC front along orographic features. Air mass is expected to remain weakly capped ... with relatively deep/dry convective boundary layers ... and little CAPE. This suggests that strong evaporative cooling will occur in the downdrafts ... with an attendant threat for quite gusty winds and small hail with the TSTMS. Greatest TSTM coverage should occur over N Italy where forcing for vertical motion will likely be strongest. Though cold-pool formation may briefly promote bow-echo-like structures ... organized severe TSTM threat appears to be quite low owing to weak CAPE and marginal shear.

...South-Central Mediterranean...
Low-level moisture is much more ample over the S-central Mediterranean as revealed by Friday's 12Z ascents from LIEE and LICT. Nose of Saharan EML plume is progged to overspread the S-central Mediterranean Sea during the period ... which will likely improve the thermodynamic profiles ... which are currently characterized by near-neutral lapse rates. Also ... 500 hPa flow is expected to increase to 25+ m/s late in the day over the S-central Med.

Main focus for TSTM development should remain the cold front which should trail from the low center over the Tyrrhenian Sea into the S-central Med on Saturday midday. Given strong deep-layer shear ... increasingly favorably mid-level lapse rates ... and a nearly saturated pre-frontal boundary layer ... chance of a few tornadic supercells exitsts. Also ... marginally severe outflow winds/hail may occur. However ... allover setup is too marginal for a SLGT.

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