CONVECTIVE FORECAST - UPDATE
VALID 13Z WED 05/05 - 06Z THU 06/05 2004
ISSUED: 05/05 12:53Z
FORECASTER: DAHL

There is a moderate risk of severe thunderstorms forecast across Greece and the NW Aegean Sea.

There is a slight risk of severe thunderstorms forecast across the S Balkan States ... W Turkey and the Aegean Sea.

General thunderstorms are forecast across W ... central and SE Europe.

SYNOPSIS

Intense jet streak at the W periphery of the upper low centered over the British Isles is rapidly digging into the central Mediterranean ... Downstream ... intense vort max currently over the Ionian Sea ... will quickly lift northeastwards ... thereby affecting the S Balkan States ... the Aegean Sea and W Turkey until Thursday early morning. At low levels ... extensive SFC low anchored over the British Isles is covering entire Europe ... with weak cyclogenesis at its periphery underway over the Ionian Sea ahead of the vort max ... fostering advection of steep mid-level lapse rates from the N Sahara into the central Mediterranean regions.

DISCUSSION

...Greece ... Aegean Sea .. Turkey ... S-central Mediterranean Sea...
TSTMS have initiated over N Greece ... apparently at the nose of the Saharan theta-e plume. Shape of the thermodynamic profiles over this regions is uncertain ... but it looks that rich BL moisture is in place with SFC depoints around 15°C ... which is capped by steep lapse rates associated with an EML. Also ... dry upper-level air has overspread the northern portions of the SFC cold front currently medirionally oriented over the central Ionian Sea ... and the nose of the 850 hPa theta-e plume ... allowing for strong solar heating of the warm-sector air mass over N Greece. This suggests that ample instability will develop especially over N Greece over the next few fours ... with MLCAPEs expected on the order of 1500 J/kg.

500 hPa flow is progged to increase to 25+ m/s ... with SSWLY 850 hPa flow increasing to 20+ m/s over the next hours. SSELY SFC flow will likely be augmented locally ny the complex terrain ... yielding shear profiles more than adequate for severe thunderstorms

Additional TSTMS should develop during late afternoon/evening over the E Ionian Sea and N Greece along the SFC cold front. However ... models indicate mesoscale region of somewhat weaker mid/upper flow to overspread this region ... limiting deep-layer shear somewhat. Nonetheless ... low-level kinematic setup will likely support rotating updrafts ... posing threat of large hail ... damaging wind gusts and a few tornadoes. TSTMS may evolve into a linear MCS with imbedded bows/short line segments late in the evening/night ... with main the threat shifting towards damaging wind gusts.

Storms farther N in the WAA regime ... will profit from increasingly benign low-level shear profiles ... and potential for supercells will increase. Large hail will be the main threat with this activity. If storms become SFC-based ... a tornado or two cannot be discounted.

...Northern Mediterranean Sea...
TSTMS will likely accompany strong vort max overspreading the northern Mediterranean late in the period ... chance of an isolated severe wind event and of an isolated tornado or two exists given strong shear and low LCL heights. However ... severe threat is too low for a SLGT.

Otherwise ... threat of organized severe TSTMS is quite low owing to weak kinematic and thermodynamic profiles.

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