Empieza el espectaculo de esta semana... por granizo grande y downburst
A level 1 was issued for N-Spain and extreme SW France mainly for large hail and a few severe downburst events.
...NE/N Spain into SW France...
Surface dewpoints in the mid-tens over NE/N Spain and upper single digits in the mountains offer a rich BL moisture content with mean mixing ratios of 7-9 g/kg within the highlighted area. The past few days showed some diurnal mixing due to strong heating, but overall depth of moist air (1 to 2 km AGL) remained more or less unchanged. In response to an approaching E-Atlantic trough, winds at mid-levels start to back (sampled by Lisboa), and a transient WAA regime is forecast (already visualized by NE-ward spreading cirrus over the Iberian Peninsula). This assists in a N-ward fanning EML plume, which overspreads the area of interest. Forecast soundings show steepening mid-level lapse rates with modest moisture content beneath a 800 hPa cap, so 500-1000 J/kg MLCAPE looks reasonable. Highest CAPE values probably evolve along the Pyrenees, where some upslope flow from the south occurs. DLS remains weak (10 m/s or less), but WAA regime inserts some veering. Combined with healthy looking CAPE profiles, a few strong multicell storms with large hail and strong wind gusts are forecast. Storms remain attached to the mountains for some time, before moving off the mountains (cold pool driven) during the late afternoon/evening hours. Thunderstorms continue into the night, although weakening betimes. Most storms should be sub-severe by then. We added far SW-France into the level 1 due to the hail risk.
Further north into France, mid-level lapse rates remain modest, but less BL moisture should keep MLCAPE around 500 J/kg. Scattered thunderstorms are certainly possible during the afternoon/evening hours (driven by orography), but nothing severe is anticipated.
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