Forecast Update
Valid: Sun 28 Mar 2010 11:00 to Mon 29 Mar 2010 06:00 UTC
Issued: Sun 28 Mar 2010 11:01
Forecaster: TUSCHY

A level 1 was issued for W-Turkey mainly for an isolated large hail and tornado event.

SYNOPSIS

A major cyclonic vortex is centered over N-Europe with two troughs to its south (one west of the Bay of Biscay and the other one over SE-Europe). Ridging is preset in-between over S/SW-Europe and no significant thunderstorm risk is forecast over Europe. However, showers and thunderstorms will occur over numerous spots, discussed below.

DISCUSSION

... Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, parts of Albania, Serbia, Macedonia and parts of Greece ...

A flat mid-/high-level ridge builds in from the WSW during the forecast with large-scale NVA present. Therefore, no upper support is seen for initiation and the focus shifts to the convective temperature. Forecast soundings and 00Z sounding data indicate a temperature of roughly 13-15°C and we're on the best way to surpass this level with temperatures now (9Z) running between 10-14°C. Also, first CU fields are seen, so shower/thunderstorm initiation will probably occur during the following 2-3h.

00Z soundings indicate a shallow moisture layer, which gets mixed out during the day, but steep lapse rates at all levels still support deep updrafts, supportive for lightning production. Deep layer shear remains below 20 m/s over most parts, despite Slovenia and W-Croatia, where 20-25 m/s are forecast, as mid/upper jet approaches from the west. Isolated large hail and strong wind gusts are possible, but we see no reason to issue a level 1 for that risk due to the modest CAPE and modest shear but also due to decoupling of strongest shear and best CAPE in the highlighted area. The thunderstorm risk diminishes after sunset.

...W-Turkey...

Large-scale upper trough crosses the Aegean Sea and is about to move over W-Turkey with already rapidly increasing convection along the coast/W-Turkey, as surface cold front moves ashore. This front becomes more diffuse due to the rough orography and therefore the risk for organized storms diminishes during the afternoon hours (also due to weak shear beneath the trough axis). An isolated large hail event and strong wind gusts are forecast. A level 1 was included but this one will expire after 18Z.

Behind the cold front, CAA is underway and models indicate a significant increase in LL CAPE build-up, especially over the SE Aegean Sea. However, the air mass is dry/continental and needs some time for moistening, so we have some concerns regarding the final degree of thunderstorm coverage. For now we went with a 15%-thunderstorm area along the coast, where coastal convergence could locally increase LL mixing ratios. An isolated waterspout is possible in this fetch and we issued a low-end level 1 for that risk.