Storm Forecast
Valid: Thu 17 Feb 2011 06:00 to Fri 18 Feb 2011 06:00 UTC
Issued: Wed 16 Feb 2011 19:52
Forecaster: GATZEN

A level 1 was issued for the southern Adriatic Sea mainly for severe wind gusts and tornadoes.

SYNOPSIS

At the western periphery of low geopotential across Europe, a short-wave trough cuts off over the Iberian Peninsula and will move into the Mediterranean Sea. A very strong mid-level jet streak will curve around the base of this trough and is expected to affect the east Mediterranean late in the period. While most of Europe is dominated by rather cool and stable air masses, a quite warm southerly flow evolves east of the developing cut-off low and will spread into the Aegean Sea region. This will be also associated with increasing low-level moisture over the southern Adriatic and the Aegean Sea.

DISCUSSION

Southern Adriatic to Aegean Sea

A steady southerly to south-easterly low-level flow is forecast by latest models that will lead to warm air advection and low-level moisture pooling resulting in more than 8 g/kg low-level mixing ratio at the end of the forecast period. A tongue of warm air masses originating from the Sahara desert will nose in the same area late in the period. This air mass is expected to be dominated by stable lapse rates initially that will likely improve during the period when the nose of the mid-level jet streak will lead to synoptic lift.

The best potential of CAPE is forecast over the Adriatic Sea near a developing surface low pressure system. Showers and thunderstorms are forecast to develop especially ahead of a cold front that moves eastward late in the period. Given strong southerly winds along the cold front at 700 and 850 hPa, strong vertical wind shear (15 m/s 0-3 km bulk shear) is expected to lead to some organized convection. A narrow cold frontal rain band is forecast with a weak chance of severe wind gusts and tornadoes. Ahead of this line, some convective cells may develop that can produce isolated hail that is expected to stay rather small.

The chance of initiation is forecast to decrease farther east as warm mid-level air masses and weak low-level convergence are indicated. The best potential is forecast over the north Aegean Sea where upslope flow along the Aegean coasts can assist for initiation. Severe storms are not expected as the low-level vertical wind shear and instability will be mostly weak.

South-west Mediterranean

In the range of the developing cut-off low, mid-level temperatures below -30°C are forecast to produce steep lapse rates. Current thinking is that the low-level moisture will be too weak over the Iberian Peninsula where some showers may develop. More intense convection is forecast over the west Mediterranean Sea, especially near the African coasts where low-level moisture will be higher. These storms will be affected by strong (10 m/s) low-level bulk shear and may produce severe wind gusts. A tornado is not ruled out as well. Convective activity is forecast to spread north-eastward during the second half of the period. Decreasing vertical wind shear will also lead to a decreasing severe weather threat.