Author: Fabian Umbricht

“When the going gets tough, the tough get going”

Synopsis:
The cut-off low west of Spain, that was dominant during the last days, gets joined by another trough and sweeps over the Pyrenees.

Castejon:
The morning is already cloudy, showers and possibly violent thunderstorms move in quickly from the Ebro Valley. The most intense precipitations and stormcells move away to the north in the afternoon, but further showers are still likely. However, some flyable windows, probably even with local, low-based thermals are possible in the second half of the day. Winds turn from south to westerly directions.

Nuria:
The early hours of the morning could still offer some windows with sunny spells, however the southwind will probably be too strong for flying. During forenoon, clouds and storms move in from southwest, with the most intense phase around noon.
The second half of the afternoon could again see increasing conditions with sunny spells and thermals – however isolated showers will remain possible until the evening. After the passing of the thunderstorms, winds will turn to west and decrease compared to the morning hours – but probably still keep strengths of 25-35 km/h. In the mountains south of TP5, the wind will remain stronger than north of it.

Goal:
In the flats of Figueres, the forenoon remains dry, but isolated showers are already possible along the coast. Towards noon, intense and violent showers and storms pass over the area. Once they passed, the sky clears, thermals are possible – but the wind will most likely remain too strong for flying (first westerly, the towards the evening probably a rather rough Tramuntana).

Concluding Remarks:
Big respect to all athletes who are still on the route and keep on pushing in this very difficult weather situation on Saturday!

And of course, congratulations to all the athletes who made already the goal!

I hope that one or the other team could get some insights from this forecasts (despite them being far from perfect) and make some smart decisions thanks to them;
and that one or the other viewer got some additional background about the weatherconditions the team had to face!

Synopsis:
With the cut-off low moving slowly into Spain, the southerly flow over all altitudes increases.

Area of Castejon:
During forenoon, conditions are still rather smooth but stable. When thermals start to develop around noon, the south wind will increase and reach around 20-40 km/h at 2500 and 40 to 50 km/h at 3000 MASL. The thermal conditions itself still look rather good with a forecasted cloudbase reaching up to 4000 MASL. Overdevelopments are not that much of a problem anymore, as the clouds are blown quickly into France, there are little to none shower signals in the model data.

Area of Valle Nuria:
The Vallies around Andorra see a similar situation regarding wind and thermals as the central Pyrenees around Castejon. On the ridges in the line of Valle Nuria/Puigmal, the southerly winds will probably stronger, even in lower altitudes. The same is valid for the mountains east of TP5.

Goal:
The flats around Figueres and direction goal will remain tricky. Seabreeze and very stable conditions will make progress by flying difficult. Again, it seems like the southerly winds will overrule the northerly Tramuntana, making for a stiff seabreeze. If there are any thermals at all, they are most likely to be found in the later afternoon.

Outlook:
The last day will unfortunately bring rather bad weather conditions. The early morning will probably still be dry around Castejon and eastwards, but showers and thunderstorms are moving in during the forenoon and spreading towards the east. Around Goal, rain will set in during the afternoon.

Synopsis:
Cut-off low moving to the Strait of Gibralter, while a (very shallow) ridge remains over the Pyrenees. The advection of warm and moist air in lower levels continues.

Area Castejon de Sos:
Not only on a large scale, also in the details Thursday looks rather similar than today. In terms of wind, there will be again mostly southerly winds of moderate strength within the thermal layer. Regarding insolation and thermals, there will be again some high clouds crossing the mountain range during the night, but they should move away and not hamper insolation. It seems that the airmass is slightly less stable in the morning than today, so it is forecasted that the thermals start slightly earlier than today.
Some Cu clouds will devlop into the earlier afternoon, locally growing into TCU, but while some thermal forecasts show rather high risk for showers, the probabilistic models show a rather low (5-20%) chance for rain around Castejon.
However it is likely that there will be some shaded areas from the middle of the afternoon onwards, probably slowing down flying conditions a bit and making things a bit more complicated.
Cloudbase is forecasted around 3500 in the high mountains and 2800 MASL in the foothills.

Area Valle de Nuria:
Rather similar conditions as around Castejon with the difference, that the risk for showers is modelled slightly higher. While there are booming conditions in the early afternoon, the later afternoon will get more complicated because of the growing shadows and probably again some thunderstorms.

Goal:
Once you leave TP5 and fly towards goal, the conditions will get increasingly stable. The area from Canigou down to Olot should still provide decent climbs up to around 3000 MASL, but once you get into the foothills, the seabreeze and a much lower base will it make progress much more difficult.
The feared Tramuntana (Northerly winds from France into Spain) in this area doesn’t seem to be very active, but in turn the large scale southerly flow could enhance the seabreeze (there are signs for a wind pattern called “Le marin” in southern France). Anyway airspaces, seabreeze and the stable conditions around Figueres will make for a challenging final for sure.

Outlook:
Significantly increasing south winds on Friday will make flying conditions more difficult, but weather around the courseline should remain mostly dry until the evening.
On Saturday, the cut-off low which dominated this week will swing over the Pyrenees, leading to widespread showers and storms moving in during the day.

Synopsis:

The Pyrenees remain between two cut-off lows, one to the east over Italy – slowly filling and with decreasing influence, and one to the Portuguese Atlantic coast, increasing it’s influence over the region. Warm and increasingly moist air from the south is advected into Spain, leading to increased cloudiness and instability.
How strong this advection is and how far it extends into the Pyrenees depends strongly on the position of the Portuguese cut-off low, which is subject to considerable uncertainty.

Area around TP2 (Pyrenees Atlantique):

During the night and early morning, some high level clouds will cross the Pyrenees. They can hinder the solar radiation, but the radiation should be enough to develop thermals in the course of the morning.
The thermal forecast looks similar to today: rather stable conditions in the lower levels, but usable thermals developing just before noon. Rather weak NNE winds should prevail in the thermal layer, while the top of the thermals will reach around 1600-2000 MASL west of TP2 and up to 3000 MASL towards Pic du Midi.
The NNE easterly valley winds will reach around 1500 MASL, above which moderate S to SW flow will prevail (the strength of the wind depends on the large-scale situation and is modelled in a range between 10 and 25 km/h at 2500 MASL).
There will be some overdevelopment, when and where it will start first depends on the model you’re looking at. Likely the area around TP2 will trigger the first showers on the French side.

Spain (Area of Castejon de Sos and towards Catalonia):

Also in the Spanish Pyrenees, some clouds will move through the sky during the early morning and forenoon.
Nevertheless, thermals should develop during the forenoon, reaching peaks around 3000-3500 MASL in the high Pyrenees and around 2600 MASL in the foothills. The lower layers in the foothills are more stable and the thermals will start later, but once developed they’ll offer good climbing rates.Southerly to south-westerly winds of 15 to 25 km/h will prevail, with the possibility of a light WNW tailwind above 2500 MASL.
The likelihood of overdevelopment along the route is also real in Spain, but the airmass is a little drier towards the east, so conditions look a little better towards TP5. Overdevelopment in the eastern parts of the Pyrenees seems to be mainly on the French side of the range and the areas towards the Mediterranean where the airmass offers more moisture.

Outlook:

With the Portuguese cut-off low moving in slowly, the outlook remains very uncertain. Some models show slowly deteriorating conditions with increasing cloudiness and storminess from day to day, while others show decent conditions until midday on Friday.
What does seem certain is that the remnants of the cut-off will pass over the Pyrenees on Saturday, leading to widespread thunderstorms and rain on the final day of the race.

Synopsis:

The Pyrenees lie between a slowly filling, but quasi-stationary, low pressure area over the Mediterranean and a forming low pressure area to the west of Spain. In between, a narrow ridge extends from the western Pyrenees to the North Sea. With the ridge still present, an inversion between 2000 and 2500 MASL is still present, but much weaker than on day 2. Meanwhile, the forming cut-off to the west leads to advection of significantly warmer air into Spain and the Pyrenees at lower levels.
At first glance, the changes on a large scale are small, but in detail the conditions will change significantly between day 2 and day 3, with the wind turning almost 180 degrees in some cases.

French Basque-Country / Pyrenees Atlantique (TP1-TP2):
At least the humidity doesn’t seem to be a big problem anymore – the weather should stay the same all day. However, the wind situation is changing significantly. In the early morning, a strong southerly wind (25-50 km/h) will arrive above 1000 MASL. The warm air associated with this southerly wind will make it very difficult for thermal activity to develop, so the whole of the morning will see fairly stable flying conditions in the lowest altitudes down to about 1200 MASL. Those who are able to take off above the overnight stable layer will see the thermals develop much earlier, but will also have to contend with the rather strong and potentially turbulent southerly wind. This effect is more pronounced the closer you are to the Spanish border.

Once a thermal boundary layer is established in the French valley, it is likely to remain capped around 2000 MASL (probably lower) and moderate (10-25 km/h) valley winds (mostly NNE) will prevail at these altitudes.Due to dynamic effects (decreasing pressure in the Lee of the Pyrenean main chain), the valley winds will be stronger than the – relatively weak – thermal activity would suggest.
Above this cap, we have significant wind shear and the persistent moderate to strong southerly wind.

The French side of the area between TP2 and the Vallee d’Aure (around Pic du Midi) appears to be very complicated with two stacked airmasses; the lower, capped and relatively stable French airmass with northeasterly winds up to about 1500 MASL and the upper, airmass with better thermals but windy conditions due to the southerly wind.However, the southerly wind is modelled to be less strong in this area than to the west of TP2.

Interestingly, above about 3500 MASL, a northerly wind prevails (hence the title “The Sandwich”).

Spanish Pyrenees (Panticosa – Monte Perdido – Boi Taull):

The good news:
Once in Spain, there’s only one air mass to keep you busy. Moderate (15-25 km/h) southerly winds dominate the thermal layer.
The advection of warmer air also delays the start of the thermals in Spain, but there should be developed thermal activity around midday, with good climb rates and a base around 2500, probably up to 3000 MASL.
With these southerly winds, flying conditions will also be quite difficult, but it’s likely to be a little easier and less complicated than on the French side.
However, there seems to be some risk of thunderstorms and showers towards the evening, especially east of the Castejon de Sos area.

Summary:

It looks like we are in for another complicated day of flying. Different layers of air masses will dominate Tuesday in France: A lower, rather stable layer up to about 1500 MASL with winds from the NNE, a layer with rather strong southerly winds between 1500 and 3000 MASL and a third layer with northwesterly winds above (the last one is rather insignificant for the race). Thermals will develop quite late in the lowest layer.
In Spain, the mountains remain entirely in the middle layer, offering a late start and windy conditions, but with rather good climbing rates.

Outlook:
Wednesday and Thursday are a bit uncertain as it’s really hard to predict what the cut-off to the west of Spain will actually do. At the moment it seems to be less windy, but increasingly stormy.

No offence to any French colleagues! In previous X-Pyr-Races, the French side of the Pyrenees didn’t show off its full potential, but became rather infamous for fog and walking. The big question for Monday: will the clouds disappear? Or will we see another chapter of (assumingly wrong) prejudices about the French Pyrenees?
Let’s elaborate.

Synopsis:
At the surface, the centre of the high-pressure system is moving off to the northeast, which is leading to a gradual decrease in MSLP over the Pyrenees. Meanwhile, at the upper level, a sharp ridge is building over the Bay of Biscay, while the cut-off low over the Med remains stationary. The wind direction is turning from north to east-northeast, which is keeping a northerly component in the lowest layers. The humidity we’re seeing today is stuck in the lowest layers between the French flats and the Pyrenees.

French Basque-Country:

In the morning, the low stratus covering the Basque country is set to extend. The cloud tops are around 1000-1500m, and the cloud base is pretty low.
The clouds should start to break up during the morning (around 1000 LT), turning into 4-6/8 Cu with the cloud base rising from about 900m to about 1500m. The thermal forecasts aren’t great, but they still show decent climbing rates of around 1-2 m/s.
However, it’s worth noting that weather models can struggle to accurately predict low stratus cloud cover, and there’s a common perception that fog in the French Pyrenees is particularly persistent. This could result in a longer-than-expected transition from cloudy conditions to more favourable thermic conditions.
Wind speeds in the boundary layer are currently between 5 and 15 knots from the east, with a more northerly component the closer you are to the Spanish border.

Spanish Basque-Country:
On the Spanish side, the airmass looks drier, but it’s still capped by an inversion at around 2000 MASL, at least in the lower mountains. The thermal forecasts show better climbing rates and a higher cloud base than on the French side, but also more significantly more wind (NE). Once you reach the higher mountains (>2000 MASL), the winds should be weaker in Spain and veer more towards the east in these regions.

Outlook:
It looks like Tuesday will be a good day for flying, with only a little cloud cover. However, the French side seems to be more stable, with only weak climbing rates and probably some wind from the south-west kicking in during the day. The Spanish air seems to be booming, as shown in the XCTherm forecast below.

We’re expecting things to get more complicated again on Wednesday with a trough over Spain leading to stormy and windy weather.

Synopsis:
The Atlantic Pyrenees are still in the area where the weather is affected by high pressure over the Atlantic and a low pressure system over southwestern France and the Mediterranean. In this area, the wind is usually from the northwest or north, bringing in rather moist air from the Bay of Biscay into the Basque Country.

Basque Country:
As the pressure rises, the humidity drops below 2000m, creating a thick low-level cloud cover over the Basque Country. The base of this cloud seems to vary in altitude, from 700 to 1200m. The humidity can rise along the mountains, causing drizzle, and local showers can also form along the coastline, especially in the afternoon.

With the northerly wind direction, some lee effects are possible in the Spanish Basque country, leading to a locally elevated cloud base. However, the cloud cover remains thick there as well, and some potential downslope winds could make things a bit more complicated. The airmass would potentially be a bit drier in the Spanish mountains around Pamplona, but first you have to get there – and once there, the northerly winds remain an issue.

To sum up, Sunday is going to be a bit of a challenge, with only a few flights likely to take off. And the Basque fern will be making an appearance as well.

Outlook:

It looks like Monday and Tuesday will be much better for flying, as the air is drying up, even on the French side of the Pyrenees. With the winds calming down, these days should provide decent flying conditions.
Towards Wednesday and further on, there are still some uncertainties in the forecast.