Storm Forecast

Storm Forecast
Valid: Thu 28 Aug 2014 06:00 to Fri 29 Aug 2014 06:00 UTC
Issued: Thu 28 Aug 2014 04:55
Forecaster: GATZEN

A level 1 was issued for northern Spain mainly for large hail and severe wind gusts.

A level 1 was issued for Turkey mainly for large hail and severe wind gusts.


The European long-wave trough slowly moves east ahead of a new Atlantic trough entering the British Isles. In between, a ridge extends into central Europe and western Scandinavia. Cool air masses have spread over all of eastern Europe except for Turkey and the Aegean region. In the range of the ridge, a plume of warmer air starts to advect north-east over France and Germany. This is also associated with a tongue of moist air spreading into France and the Benelux countries ahead of the British Isles trough. Steep lapse rates can be only found over the Mediterranean region, but CAPE is strongly capped over most areas.


Northern Spain

Latest soundings across eastern Spain indicate deep inverted-v profiles over the Iberian high plateau and an impressive elevated mixed layer near the Mediterranean Sea. However, a strong capping inversion is also in place, and given weak lift expected today, chances of storms are low.

The best potential for initiation exists over north-eastern Spain. Rich low-level moisture from the Mediterranean Sea is expected to advect upslope during the day ahead of the thermal low over the high plateau. Over the mountain slopes, low-level convergence may be strong enough to break the cap that will be weakest in the afternoon in response to diurnal heating. Additionally, a weak mid-level trough will enter northern Spain in the afternoon from the west, what can also assist in breaking the cap due to weak frontogenesis along the northern boundary of the very warm Spanish air mass.

Current thinking is that a few storms will develop over north-eastern Spain in the afternoon. In the evening, initiation may also be possible further west over northern Spain. Storms will have a potential to become severe given 15-20 m/s deep layer bulk shear and around 15 m/s 0-3 km bulk shear due to easterly low-level winds and an increasing westerly flow ahead of the approaching mid-level trough. Storm-relative helicity is increasing in the evening hours indicating the potential of supercells.

Large hail is expected to be the main threat. Storms over the high plateau may produce local dry downbursts due to the large inverted-v profiles. Storms will move eastward with the main flow and may decay due to the increasing cap near the Mediterranean Sea. However, together with the short-wave trough moving into the north-west Mediterranean, a few storms may survive over the Sea for some time until the night hours, especially where the land-sea-breeze convergence assists in low-level convergence.


The east-European long-wave trough moves slowly east, and its southern base will affect Turkey today. Latest models indicate some mid-level cooling, indicating at least some lift due to large-scale forcing. At lower-levels, a warm air mass is situated over Turkey, with an elevated mixed layer over the southern and eastern parts and rather stable lapse rates in the northern and western regions. Rich boundary-layer moisture spreads inland from the Black Sea as well as from the Mediterranean in the south. An overlap of moisture and steep lapse rates can be expected over the mountain regions of central Turkey today.

Current thinking is that scattered storms will develop during the afternoon hours. Storms in the northern portions form with weaker CAPE as in the south, but vertical wind shear will be stronger (up to 15 m/s in the lowest 3 km together with curved hodographs and SRH near 150 mē/sē). Therefore, especially in the northern portions, large hail is expected with supercells and well-developed multicells. Additionally, severe wind gusts are possible due to locally dry and well-mixed boundary-layers, especially in the central parts.

Storms are expected to decay during the night hours in response to low-level stabilization.

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