Storm Forecast
Valid: Sun 25 May 2008 06:00 to Mon 26 May 2008 06:00 UTC
Issued: Sat 24 May 2008 15:22
Forecaster: DAHL
SYNOPSIS
Deep and intense upper-level long-wave trough is positioning itself over the E Atlantic/SW Europe, maintaining advection of warm/unstable air into SW and parts of central Europe. Another, albeit weaker, upper low will be located over western Turkey on Sunday. A deep upper ridge is building over the Mediterranean, between the SE and the SW European upper lows. At low levels, a weak cyclonic circulation is attendant to the SW Euroepan upper low, with weak high pressure prevailing over the Mediterranean.
DISCUSSION
... France ...
Weak instability should exist/develop over France during the day, the build-up of which may be delayed somewhat by convective debris/frontal cloudiness. Strong Q-vector convergence will spread northwards along the western edge of the warm/moist plume along the eastern Iberian coast into France late Sunday night/early monday morning. Substantially less well-defined Q-vector convergence is simulated during the day over France. It seems that scattered thunderstorms should develop during peak-heating hours over central France ... DLS of 20 m/s will initially exist over southern France, but current simulations suggest that storms will move into increasingly less sheared environment as the day progresses. However, well organized multicells and possibly a few mesocyclones should be expected, posing a threat for large hail and damaging winds. Anticipated weak capping and rather low LCL heights hint at a slightly enhanced threat also for tornadoes, but weak LLS should limit allover tornado threat. Late in the evening/night, convection may rejuvenate in response to strong frontogenetic forcing along the cold-frontal boundary stretching from central France southward into the western Mediterranean. One or more elevated MCSs may result, with the main severe threat being large hail.
... NE Spain ...
Modified polar air will overspread Iberia in the wake of the cold front, and numerous showers and thunderstorms are expected within this air mass beneath the upper thermal low. Over eastern Spain, DLS will be rather strong (30 m/s), but depth of convection should be reduced somewhat over this region. Best chance of reasonably deep convection within the strongly sheared regime seems to exist over NE Spain. Storms in this environment may be capable of marginally severe hail along with strong/severe wind gusts.
... N Balkans ...
Scattered, mainly diurnally driven thunderstorms should develop over the N Balkans during the day. DLS should be on the order of 15 to 20 m/s, so that multicellular storms and a few mesocyclones may occur, capable of marginally severe hail/wind. It seems that mid-level ridging will limit coverage of convection, and given quite marginal thermodynamic support, a categorical risk does not seem to be warranted at this time.
... N Italy ...
Over N Italy, shear should be somewhat stronger, and model guidance supports some confidence in scattered thunderstorm development. If storms develop, they will be capable of large hail and damaging winds.
... N Romania ...
About 1000 J/kg weakly-capped CAPE should persist over the Romania, where 20 m/s DLS are anticipated. Though storms should be rather numerous, resulting in a tendency to cluster into weakly organized MCSs rather quickly, the strong shear may at least temporarily sustain better organized storms, capable of large hail and severe wind gusts.
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