More of the same: Heat, high cloudbase, thunderstorms. Some changes in the prevailing wind directions can lead to headwind in the French part of the route.
Synopsis:
The upper level ridge and the subsequent heat-dome remain dominating. The synoptic changes towards Day 3 are marginal, but have astonishing effects to the flow pattern along the Pyrenees. The southerly winds are (finally) shutting down, even over the lower Euskadi hills. Instead a East-north-easterly flow settles in, which is much more relevant on the northern side of the Pyrenees.
Details:
Hot conditions with lots of insolation in the forenoon persist. Temperatures are again widespread soaring to 35-40°C in the lowest altitudes, 0°C-isotherme remains around 4500 MASL.
Thermals:
The morning inversion is again rather strong, with a top around 1500 MASL. In the lower hills between TP 1 Larun and TP 2 Villanua, the gradient is developing only slowly, taking probably until around 12:00 LT until consistent thermals below 1500 MASL are established. In the high mountains, gradients and thermal activity should develop already in the forenoon, approx. 2h earlier than in the lower layers.
In the afternoon, cloudbase is again well above 4000 MASL in the high mountains and around 2500 MASL in the lower mountains between TP1 and TP2.
Again, overdevelopments and thunderstorms are expected to form during the afternoon, mostly affecting the central Pyrenees around Añeto. The trigger for the overdevelopments seems to be convergences of the northeasterly winds with the southerly valley wind systems. Therefore, all the areas north of the main spine (mainly the French Pyrenees) are much less affected by the overdevelopments than the Spanish side. The thunderstorms are moving with the upper-level flow towards the south-west.
Winds:
While the hills of the Basque country see (for once) a rather calm morning and forenoon (south wind is shutting down), there is already a pronounced easterly flow established in the early day along the French foothills of the Pyrenees. In combination with the thermic wind systems, this leads to winds spilling over the cols and passes from the north towards the Spanish valleys, leading to the aforementioned convergences in the afternoon. The mountains between TP 1 and TP 2 are expected to be more and more influenced by these overspilling northeasterly winds during the afternoon. The higher mountains are less affected by these overspilling-effects, but there is nonetheless around 15-30 km/h of easterly winds at 3000 – 4000 MASL expected, especially over France. Over Spain, the upper level winds are more turned towards north and slightly weaker – but here, the overdevelopments are probably much more important than the upper level wind patterns.
Outlook:
Wednesday is still expected to look quite similar to Tuesday. On Thursday, Day 5, the Atlantic low reaches the most western parts of the Iberian Peninusla, leading to the onset of a moderate, probably locally strong, southerly flow and increased instability. This southerly flow will probably remain active for the rest of the race, with the details (amount of humidity, instability and upper level dynamic forcings) still a bit unclear between the models.
