Storm Forecast
Valid: Thu 03 Jul 2014 06:00 to Fri 04 Jul 2014 06:00 UTC
Issued: Wed 02 Jul 2014 22:38
Forecaster: GATZEN

A level 2 was issued for north-eastern Spain mainly for very large hail and excessive precipitation.

A level 1 was issued for eastern Spain and southern France mainly for large hail and to a lesser extend severe wind gusts, excessive rain, and tornadoes.

A level 2 was issued for north-eastern Russia mainly for large hail and to a lesser extend tornadoes and severe wind gusts.

A level 1 was issued for Romania and Bulgaria mainly for large hail and excessive precipitation.

SYNOPSIS

Mid-level flow over Europe changes due to downstream development ahead of an intense Iceland trough. Rising geopotential over central Europe will push the European trough to the east as one part moves into north-west Russia and the other digs to the western Black Sea. A cut-off low situated over Iberia will become a lifting trough at the end of the period, with a very strong mid-level jet streak spreading north-eastward.

At lower levels, a cold front crosses most of the Balkan Peninsula on Thursday, whereas warm air advection takes place over most of central and western Europe. A plume of steep lapse rates will spread into the west Mediterranean. Low-level moisture will be limited, with best moisture situated over the west Mediterranean.

DISCUSSION

Eastern Spain and southern France

Ahead of the Iberian cut-off low, a plume of hot and well-mixed desert air spreads into the west Mediterranean. A baroclinic zone forms east of Iberia, and a frontal wave will move north-east in the afternoon, leading to warm air advection. QG forcing is expected at the left exit of a strong mid-level jet streak will overspread eastern Spain. With easterly surface winds, rich moisture from the west Mediterranean continues to spread onshore.

Instability will develop in response to diurnal heating over eastern Iberia. Capping will be not too strong given rather cool mid-level air that will even cool during the period as the cut-off starts to move north-eastward. Expect CAPE in the range of 1000 J/kg, storms will be likely given QG lift, upslope flow, and numerous convergence zones due to the sea-breeze and outflow boundaries.

Strong deep layer vertical wind shear with 15 m/s 0-3 and 25 m/s 0-6 km bulk shear will allow for storm organization. Supercells are forecast due to curved hodographs and 0-3 km SRH of more than 100 m²/s². Very large hail is expected especially with isolated storms. However, convection will likely merge into a cluster given the strong forcing, with excessive precipitation and severe wind gusts possible.

Storm clusters will spread northward into southern and central France. Especially in the eastern portions, strong vertical wind shear will assist storm organization, and severe wind gusts and large hail are not ruled out. A tornado is not ruled out although low-level buoyancy is limited. The potential of excessive rainfall will gradually decrease due to weaker low-level moisture and upslope flow compared to eastern Spain.

Romania and Bulgaria

Ahead of the approaching cold front, a plume of warm air spreads into eastern Bulgaria and Romania. Low-level moisture will improve ahead of the cold front due to some convergence, and lapse rates will also increase in response to diurnal heating. Initiation is likely ahead of the cold front in the noon and afternoon given strong QG forcing and topographic support. Storms will merge to clusters that can produce excessive precipitation. Additionally, large hail and severe wind gusts are possible especially in the southern portions where vertical wind shear is best. Storms will weaken after sunset, when cold air advection will become dominant.

North-western Russia

An intense negatively tilted short-wave trough rapidly crosses north-western Russia in the morning and noon hours. Affected air mass is unstable with a plume of steep lapse rates overspreading a tongue of low-level rich moisture. Given quite strong vertical wind shear of more than 15 m/s in the lowest 3 km, well-organized storms are forecast. These may be capable of producing large hail and severe wind gusts. Along the northern edge of the warm air mass, strong low-level vertical wind shear may also support tornadoes. Convective activity will spread east in the afternoon.