Storm Forecast
Valid: Thu 24 Jun 2010 06:00 to Fri 25 Jun 2010 06:00 UTC
Issued: Wed 23 Jun 2010 17:51
Forecaster: GATZEN

A level 1 was issued for eastern Baltic states, Belarus, Ukraine mainly for isolated large hail and flash floods.

A level 1 was issued for NW Iberian Peninsula mainly for isolated large hail.

SYNOPSIS

Between a ridge over the Atlantic Ocean and a ridge over eastern Europe, rather cool and dry air masses are present over most portions of Europe including the Mediterranean. Over eastern Europe, a warm front is present at the western flank of the ridge, and a tongue of very moist air has developed.

DISCUSSION

Baltic States to Black Sea region

To the south of the broad high pressure area centred over north-western Russia, a low pressure system moves eastward over the northern Black Sea. This yields an easterly low-level flow that is directed towards a frontal boundary stretching from the Baltic States towards Belarus, the central Ukraine, and the northern Black Sea. On Thursday, this frontal boundary will be almost quasi-stationary.

Latest soundings indicate steep lapse rates that do overlap with ample moisture near the frontal boundary, and CAPE in the order of 1000 J/kg has developed. Thunderstorms have formed on Wednesday especially in the southern portions of the discussed region. On Thursday, diurnal heating will likely result in CAPE values of about 1000 J/kg again. Given the weak QG forcing expected by latest model output, main foci of initiation will be the frontal convergence as well as numerous outflow-boundaries present to the east of the front. The chance of initiation is expected to decrease to the east given decreasing boundary-layer moisture.

With weak vertical wind shear, storm mode will likely be unorganized, but a few pulse storms may produce isolated large hail. Additionally, local flash flooding is not ruled out due to the slow propagation speed. In the evening hours, an increasing low-level southerly jet may evolve along the warm side of the frontal boundary, and some storms may evolve rotating updrafts with an increasing chance of large hail. An isolated tornado is or ruled out. Storms are forecast to decay during the night hours over most places, while some storms may cluster near the Black Sea region, posing a threat of excessive rain.

Northern Iberia

Strong diurnal heating will likely lead to CAPE given some low-level moisture and a deeply mixed air mass. Storms may develop especially along a convergence zone over the north-western portions where the sea-breeze and upslope flow will be present. Additional QG forcing may result from a weak mid-level low to the west. Storms may produce large hail given the strong buoyancy. Additionally, some downbursts may occur with a slight chance of severe wind gusts. Storms will likely weaken after sunset.