Storm Forecast
Valid: Wed 16 Jul 2008 06:00 to Thu 17 Jul 2008 06:00 UTC
Issued: Tue 15 Jul 2008 21:43
Forecaster: GATZEN

SYNOPSIS

High geopotential is present over eastern Europe. To the north-west, an intense polar long-wave trough will extend south-eastward, and cold maritime air mass will advect into Baltic Sea region, Germany, British Isles, and northern France. To the south, rather warm air mass affects eastern and southern Europe. Two upper cut-off lows over Iberian Peninsula and western Ukraine, Romania, and Bulgaria are filled with cooler air mass.

DISCUSSION

Northern Morocco, south-western Mediterranean

A strong south-westerly jet streak is expected to rotate around the southern flank of the Iberian cut-off and ejects into south-western Mediterranean during the period. It is associated with strong vertical wind shear reaching more that 40 m/s in the lowest 6 km, 30 m/s in the lowest 3 km and around 10 m/s in the lowest km given north-easterly surface winds. Affected air mass is characterized by rich boundary-layer moisture especially over the sea that is advected towards the African coast during the period. Above the boundary-layer, southerly winds advect hot elevated mixed layer into the area, leading to strong CIN and rather high CAPE values. During the day, expect that rather strong forcing will be present in the range of the jet streak and low-level convergence and upslope flow. However, initiation is questionable at this time over most of the area. Best potential for deep convection is forecast over the mountains, and thunderstorms may spread northward along the outflow-boundaries during the evening hours. Given strong vertical wind shear, supercells are likely capable of producing large or very large hail and severe or even extreme wind gusts. Tornadoes are not likely, but conditions may be favourable in the range of outflow-boundaries, where low-level buoyancy and shear may be strong as well as over the Mediterranean region and south-eastern Spain, where low-level veering profiles are expected. Limiting factor for Iberia is uncertainty of unstable air mass.

Northern Turkey

In the wake of the upper cut-off low, cold air advection is forecast over northern Turkey. This air mass I forecast to be rather moist at low levels, and instability is likely during daytime underneath the upper trough axis, where relatively cold mid-level air mass is present. Low-level convergence and upslope flow will likely be supportive for convection to develop. Given strong mid-level westerly winds, multicells are likely, capable of producing isolated large hail and severe wind gusts. Thunderstorms will likely decease in the evening hours.

Northern Ukraine, western Russia

In the northern area of east European high, warm and unstable air mass is present and will spread northward over western Russia ahead of the cut-off low. In the warm air advection regime a well as along the cold front extending into northern Ukraine, moderate low-level vertical wind shear and favourable veering profiles are forecast. Deep layer vertical wind shear will be weak, and QG forcing is also weak in the range of weak mid-level ridge. However, given weak CIN and some low-level forcing, thunderstorms are quite likely during the day. Short-lived pulse storms and mesocyclones will pose the main threat capable of producing isolated large hail. A tornado is not ruled out along the warm front, where low-level SRH values are expected to be strongest. Thunderstorms will likely decay during the night hours.

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