Storm Forecast
Valid: Sat 05 Jul 2008 06:00 to Sun 06 Jul 2008 06:00 UTC
Issued: Fri 04 Jul 2008 23:04
Forecaster: DAHL
SYNOPSIS
Broad upper westerly flow is stretching across the southern portions of Europe, with increasing ridging over the Mediterranean ahead of an intense, amplifying upper trough over the E Atlantic. At the same time, an upper trough will dig southeastwards from Germany into the Black-Sea region during the period. At low levels, the Atlantic upper feature will be accompanied by a rather intense low-pressure system over the British Isles, while the rest of Europe remains under essentially quiescent conditions. Main baroclinic zone at low levels will be associated with the cold front, at 12Z expected to stretch across SW Europe, and then farther eastward across the Alps into the Balkans. Except over the Balkans and France ... this front will make little progress during the period.
DISCUSSION
... Benelux ... extreme NW France ...
Some instability is expected to develop over Benelux in plume or warm/moist air amidst 20-25 m/s deep shear. However, CAPE should be rather weak, and unstable parcel layer depth also seems to be rather low. Still, isolated thunderstorms may occur, and some chances for an isolated marginally severe hail/wind event should exist. At the moment, signals appear to be too weak for a categorical threat, but an upgrade may be needed for this region if instability turns out to be deeper than currently simulated. Thunderstorms may extend across the British Isles, where favorable kinematic fields are not expected to coincide with instability, however.
... N Iberian Peninsula ...
Some severe threat seems to unfold over N Iberia where ample DLS will be present along with weak to moderate instability. Upslope flow should aid in afternoon initiation, and given favorable shear, storms may organize into multicell clusters, possibly with imbedded mesocyclones. Main threat should be isolated large hail and severe straight-line winds.
... N Italy ...
Very unstable air should persist over N Italy, with MLCAPEs exceeding 2500 J/kg. Mid-level ridging should limit chances for convective initiation, but some LL convergence is simulated, along with convective precip. Deep shear should remain below 15 m/s, so degree of organization may be limited somewhat ... but local flow augmentations at low levels may well support a mesocyclone or two, which would be capable of very large hail and damaging wind gusts given the strong thermodynamic fields. Some uncertainty exists on the coverage of the storms ... they might fail to initiate at all. Nonetheless, a level-one area seems to be warranted.
... Poland ... Belarus ...
In the vicinity of a small upper low over the three-corner region of Poland/Belarus/Ukraine, scattered thunderstorms should persist. Though instability should be rather meager, LLS should become marginally supportive of an isolated tornado or two - especially towards the evening when LLS increases and LCL heights decrease. Coverage/strength should be too insignificant for a categorical risk, however.
... S Scandinavia ...
An isolated funnel cloud/tornado could also occur over S Scandinavia, especially in the late afternoon hours as LLS is expected to increase. However, weak DLS should limit longevity of the cells and reduce the allover severe threat so that a categorical risk is not introduced at the moment.
... Balkans ...
Some 15 to 20 m/s DLS should overlap with weak to moderate instability over the Balkans. Diurnal heating as well as DCVA-forced ascent should aid in scattered convective development. Expect multicellular storms and isolated mesocyclones capable of severe wind gusts along with large hail.
... N Black-Sea region ...
It seems that strong deep-layer lift associated with DCVA and low-level frontogenesis will overspread/develop over the N Black Sea region late Saturday night/early Sunday morning. Thermodynamic fields should be rather strong with CAPEs as high as 2000 J/kg. In addition, 20 m/s DLS should advect into the region. Thinking is that one or more large MCSs will result, which may tend towards remaining slightly elevated. Main severe threat - apart from flash flooding - should be large hail. However, isolated severe wind gusts cannot be discounted, either.
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