Valid: Fri 05 Jul 2013 06:00 to Sat 06 Jul 2013 06:00 UTC
Issued: Thu 04 Jul 2013 21:04
The westerlies will be displaced far north and influence the weather from Ireland to Finland. Further south, especially over Spain and Portugal, a strong ridge remains in place. For the rest of Europe, weak mid/upper level height gradients prevail. Along the surface a gradually strengthening and eastwards expanding high pressure area takes over the control. Thunderstorm activity remains confined to its eastern side.
... Lightning areas ...
Scanning through forecast soundings does not reveal anything interesting ingredients-wise. Coupling of moderate mid-level lapse rates and a seasonably moist BL result in widespread 500 to 800 J/kg MLCAPE. Of note is the adequate depth of the BL moisture to keep diurnal mixing on the lower end side. Regionally enhanced convergence may boost MLCAPE to values in excess of 1000 J/kg. No significant shear is expected despite modest directional shear, so degree of storm organization will be low. However, fat CAPE areas in the mid-levels and slow storm motions yield an adequate risk for isolated large hail and locally heavy rainfall amounts. Also with expected CAPE profiles, not much enhancement of the environmental wind field is needed for an isolated severe thunderstorm event (e.g. those which ride along a mesoscale convergence zone). Lack of any foci (despite degenerating convergence zones) kept us from issuing a level 1. During the late afternoon and evening hours, a few messy looking thunderstorm clusters might evolve with erratic and cold-pool driven propagation. During the mature phase of those clusters, concentrated swaths of strong to isolated severe wind gusts and isolated large hail are still possible...beside heavy rain. The thunderstorms gradually diminish in coverage and intensity during the night but areas from E-Poland into Belarus could easily see constant re-development until 06Z. This activity however remains sub-severe. We expanded the lightning area all the way to Finland to account for isolated activity after midnight due to a sharpening front, which moves slowly east.
Another area with isolated thunderstorm activity arises over N/C Portugal between 15 and 00Z. Yesterday's surface observations showed Tds in the mid to upper tens. Despite unfavorable placement beneath the upper ridge, steepening mid-level lapse rates and aforementiond BL moisture quality might support moderate/elevated and capped MLCAPE build-up. GFS is the most excited model regarding initiation, but expected strength of cap and lack of any forcing looks hard to break the cap (although a few mountain peaks might remain just at the top of the capped layer). A very isolated and short lived thunderstorm event can't be ruled out. If any updraft can survive entrainment, a strong downburst or two could occur due to high based storms and dry subcloud layers. Current thunderstorm coverage remains too low for issuing anything else than a 15-% lightning area.