Storm Forecast
Valid: Wed 06 Jun 2007 06:00 to Thu 07 Jun 2007 06:00 UTC
Issued: Tue 05 Jun 2007 20:37
Forecaster: GATZEN

SYNOPSIS

High over Scandinavia remains during the period. There are several weak upper cut-offs situated over northwestern Europe. A broad area with low geopotential is present from Balearic Islands to Adriatic, and Aegean. While a strong westerly jet is present at the southern flank of this upper low, easterly flow to the north of the low is weak.

DISCUSSION

Northern/central Italy, Alpine region and southern Germany into eastern/southern France, northern Spain

Latest soundings indicate low-level inverted-v-profiles with rather rich boundary-layer moisture and quite steep lapse rates especially below 600 hPa. This will result in CAPE during the day due to diurnal heating. Weak CIN is present, and convective initiation is expected in the range of low-level convergence zones/outflow boundaries of old convection or upslope flow regimes in hilly terrain. Quite strong buoyancy at relatively low levels will likely result in strong updrafts initially, while weak vertical wind shear is expected to inhibit organized convection over most places. Isolated large hail can not be ruled out with convective cells in the early mature stage, as well as a few strong downbursts in regions with well-developed inverted-v-profiles. Best potential for a few weakly organized multicells exists near the Alps where at least 10 m/s 0-6 km vertical wind shear is expected in the evening hours in the range of a weak upper wind maximum. However, chance for severe weather is expected to be very weak over a broad region, though. Intense precipitation and local flash flooding is forecast to be the main threat during the period.

Northern and central Turkey

Strong diurnal heating is expected over central Turkey during the day, resulting in a deep mixed layer up to the 600 hPa level. Ahead of the low geopotential over Aegean, an EML will likely spread over northern Turkey/southern Black Sea. Latest observations indicate that low-level dewpoints do reach 16..20°C near the Black Sea, and GFS model run indicates CAPE up to 1000 J/kg during the afternoon hours. Expect that instability will develop, and that the cap will be not too strong, low-level convergence and upslope flow due to north-easterly surface winds as well as upper support due to a mid-level southerly jet streak that spreads over central Turkey in the afternoon hours may lead to initiation of thunderstorms. Favorable veering with locally 100 J/kg 0-3 km SRH is expected by latest GFS, and isolated supercells capable of producing large or very large hail are not completely ruled out. The chance is forecast to be rather low, though. A greater threat is expected to result from severe downbursts that develop due to well-mixed and dry air mass over a deep layer. Thunderstorms will likely weaken after sunset.