CONVECTIVE FORECAST
VALID Sun 03 Jul 06:00 - Mon 04 Jul 06:00 2005 (UTC)
ISSUED: 02 Jul 18:48 (UTC)
FORECASTER: DAHL
There is a slight risk of severe thunderstorms forecast across the Aegean and adjacent regions.
SYNOPSIS
General high-amplitude upper flow pattern will not change much during the period ... but altogether move E/SE ... so that S-Balkan upper low will drop into the Aegean ... with the vigorous Atlantic trough spreading into France and Benelux. Weak upper low SW of the Iberian Peninsula is expected to phase with the Atlantic trough ... and cross WRN Iberia late in the day/night. Main feature on the SFC maps will be intense low NW of the British Isles ... which is progged to track towards Iceland on Sunday. Main frontal boundary should stretch from the North Sea SWWD ... with weak pressure falls anticipated ahead of the front over central France late Sunday afternoon/evening. Rather large ... but weak cyclonic circulation should persist over SE Europe in association with the upper low.
DISCUSSION
...Aegean and adjacent areas...
Saturday's 12Z ascents across the Aegean reveal weakly unstable inverted-V type profiles ... which have locally been underrun by somewhat cooler but more moist air ... yielding MLCAPE on the order of 1500 J/kg. Expect this general setup to persist/re-establish on Sunday. Shear profiles should be sufficient at the periphery of the low-pressure system to support severe TSTMS ... with mesoscale processes being likely to augment/weaken low-level shear profiles locally. Given anticipated variety of kinematic/thermodynamic environments ... severe threat should likewise vary. Expect a few mesocyclones and bow echoes ... which should primarily support large hail and severe wind gusts ... though an isolated tornado cannot be excluded.
...France...
Models agree in the evolution of weak CAPE towards Sunday afternoon over France. NLY SFC flow is expected to continue across S France through much of the day ... with return flow beginning late on Sunday. This suggests that advective increase of BL moisture should be mimimal during the day ... and that any increase of moisture will likely be related to evapotranspiration. Quantitative contribution of this factor is uncertain ... but thinking is that low-level moisture will probably not increase dramatically. BOLAM suggests that EML from Iberia will likely not make it across France ... so that significant advective steepening of the lapse rates is unlikely. As large-scale vertical motion should also remain fairly weak until late Sunday night ... afternoon profiles across France are expected to remain largely unchanged. However ... weak CAPE may locally be possible along developing SFC convergence over NRN France which may favor accumulation of sufficiently deep moisture to sustain deep convective updrafts.
Large-scale ascent is expected to be minimal during the day ... but to increase during the night. Isolated/scattered TSTMS may form during peak heating hours over central and NRN France along mesoscale convergence despite weak upper support ... and may congeal into a nocturnal MCS which may persist through the night and affect NRN France as well as the Benelux States.
Given minimal thermodynamic support ... kinematic fields are somewhat marginal ... with about 15 m/s deep shear. Nonetheless ... isolated large-hail/severe-wind events may be expected ... especially with the MCS that is anticipated after dark. However ... ATTM it seems that shear in the cloud-bearing layer will be too low for an organized severe weather threat.
...Spain...
LEMD 12Z ascent is not available ATTM and shape/development of thermodynamic profiles across central portions of Iberia are somewhat uncertain. Models coherently advertise weak CAPE/precip over NRN Spain. Assuming unimpeded insolation ... very deep CBLs may develop ... with sufficiently high SFC theta-e's to allow for weak CAPE. Expect an isolated Cb or two to develop late in the day ... which will briefly pose a threat for severe wind gusts. Threat is too conditional and isolated however for a categorical risk.
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