The return of the south wind. All the while, sun, heat, morning stability and overdevelopments remain to be dealt with.
Synopsis: With the Atlantic low reaching Spain, the wind over the Pyrenees turns to south and is increasing. Geopotential over the central and eastern Pyrenees remains still rather high.
Details: Once more, a sunny and hot day can be expected. Temperatures remain around 35-40°C in the flats (ca. 36°C in Figueres), 0°C-isotherme still at 4500 MASL. Insolation is pretty much undisturbed until the formation of diurnal clouds in the afternoon.
Thermals:
In the widespread overheated airmass, the gradients remain very small in the lower layers for the first half of the day. The inversion layer is expected to be somewhat higher than the days before and is forecasted around 1500 – 2000 MASL. Above, gradients are better and allow thermals starting earlier. However, the southerly winds start to advect around slightly warmer air at altitudes from 1500 to 2500 MASL, which can dampen the thermals even above the inversion until noon.
Nonetheless, a widespread good gradient can establish on the Spanish side of the Pyrenees above 1500 MASL and thermal tops of 4000 MASL are again possible. On the French side of the Pyrenees, the warming at mid-altitudes due to the south wind is more pronounced, leading to a stubborn inversion layer remaining at around 1500-2000 MASL.
Overdevelopments remain possible and can be problematic. With the change to southerly winds, the convergence zones leading to these overdevelopments shift to the north. Especially the French side of the Pyrenees shows across different models overdevelopments and showers in the later part of the afternoon. The Spanish shows only little risk for overdevelopments in the model, but some isolated towers can not be ruled out.
Winds:
The main factor influencing flying on Thursday will be the increasing south wind. In the forenoon, winds in the central, eastern and northern parts will probably still be rather calm on layers below 1500-2000 MASL. Higher ridges, as well as the western parts will already see moderate south winds in the forenoon, quickly picking up during the day.
In the lower mountains, and most of the Spanish Pyrenees, the overlapping of thermic valley wind systems and the synoptic forced south winds can create strong winds and very rough conditions from noon onwards.
On the French side, it is possible that some valley will develop rather strong northerly valley winds in the lowest altitudes, while at higher altitudes (above 2000 MASL) moderate to strong is present. Other valleys probably see the valley wind completely overruled by the south wind.
For the last miles between TP 6 and the goal, the southerly wind is completely overruling the classic northerly Tramuntaña, but the strength of the southerly wind is increasing quickly in the afternoon: Countering one bad with another doesn’t necessary result in a good thing…
In the afternoon, winds at 3000 MASL are forecasted to be around 30-40 km/h east of Castejon de Sos, and 40-50 west of it. At 2000 MASL, local accelerations can also lead to 35-50 km/h along ridges or above the inversion layer in France.
After 15:00 LT,
Outlook:
Strong southwind prevailing on Friday and Saturday, with Friday looking slightly better than Saturday. Thermal conditions remain rather similar, but the wind is reducing the usability of the thermals significantly.
