Climate of the Pyrenees

Latitude, position on the continent and orographical orientation generate in the the Pyrenees an important climatic contrast (thus vegetable) on both sides of the high chain: the oceanic influence is dominating in the west and north, while the south and the east are subjected to influences Mediterranean and continental.

Weather situations “standard”

Flow of south-west in west : regularly carrying disturbances of Atlantic origin, degraded at the time of their crossing of the Iberian peninsula then reactivated in contact with the Pyrenean relief. They bring the main part of precipitations on the buttresses of Navarre, Aragon, the west of the Catalogne, Andorre and the major part of the frontier peaks.

Except in the case of the very active disturbances which can overflow, the French slope benefits from traditional a Effet of Foehn (sun veiled, weakening downpours). But this current of high-altitude (especially when it is not very disturbed) can also combine with a flow of the basic North-West altitude, under the high chain creates for itself a “in-draft” which will collect the moisture of the the Bay of Biscay near and generates one second disturbance, typical septentrional slope and which never overflows in the south (curious situation of a sea of clouds covering valleys and medium mountains, dominated by a cloudy ceiling of altitude, with an interstice released between the two).

Flow of the North-West in north : compound, independent or succeeding a disturbance of west-south-west. The clouds “are aspired” under the refief or accumulate against him and cause the main part of precipitations on the septentrional slope (France and Val of Aran).

Flux of the North-East with is : generally anticyclonic. Following a disturbance of north, the activity declines by the North-East then the good weather returns by the east. Occasionally another situation can arise, of the autumn in spring: after a descent of cold air on the Mediterranean (Gulf of Lions), a depression digs and generates intense disturbances, though of a low capacity of penetration in the grounds: they affect especially is chain.

Flow of south-east in south : generally little disturbed and heralding a degradation by south-west. More rarely they are large southernmost depressions (of Mediterranean or Atlantic origin). These potentially torrential disturbances touch initially the southernmost slope of the Pyrenees and the frontier peaks, more still in the oriental party close to the sea. They can also overflow on the septentrional slope.

Climatic areas

Mountains basco-navarro-inhabitants of Béarn of Rhune with the Ossau and Ansó (oceanic climate): because of their moderate altitude which limits the effect of barrier, they are exposed at the same time with the disturbances of west-south-west and those of north-north-west, these last being particularly active with the proximity of the ocean. The office pluralities of precipitations are highest of the Pyrenees: averages from 150 to 250 cm/year (optimum around the Peak of Annie). The annual thermal amplitude, limited by the oceanic air, is of approximately 12° (Isotherme 0° around 1350 meters of altitude in January - isotherm 10° around 1700 m in July).
winter, irregular snowing up because of the relative oceanic softness, but supplied with the abundance of precipitations, is durable above 1200 meters environ.
“luxuriant” Végétation (oaks with null and void sheets, beeches, fir trees).
northern Medium mountains of the Ossau to the Western Aude (climate suboceanic): relatively saved by the disturbances of west-south-west which discharge before on the high frontier chain, it is intensely exposed to the disturbances of north-north-west which come to butt against the relief. This effect of “stopper” is made feel until on Piedmont (under-Pyrenean pluviometric pad: 124 cm/year with Lannemezan) and are accentuated in the funds of valley opened well with the north-north-west, kinds of “funnels with clouds” where are observed the annual office pluralities most important (168 cm with Aulus Baths in Ariège). The first buttresses also are very sprinkled (154 cm/year with the Chiroulet in the Hautes-Pyrénées), while the encircled broad valleys of solid masses are sheltered (92 cm with Saint-Lary-Soulan, 90 cm with Luchon, 78 cm with Tarascon-on-Ariège). The pluviometric average is from 100 to 150 cm/year. The thermal amplitude increases compared to the Pays Basque to reach 13 with 14° (isothermal 0° around 1200 m in January - isotherm 10° around 1850 m in July). The winter snowing up, helped well by the wet and fresh flow of north, is durable above 1200 mètres.
green Paysages (Chêne S with null and void sheets, Hêtre S, Sapin S).
southern Medium mountains of Ansó with Cadi (climate subcontinental with Mediterranean tendency): contrary to an generally accepted idea, the Spanish slope (certainly sunnier) is not systematically drier than the French slope, at least in terms of pluviometric office pluralities. The disturbances, mainly of west in south-west, are in fact rarer but more intense than in France. The effect of accumulation against the relief plays less and one needs important solid masses to reactivate these disturbances of average or high-altitude: that explains the dryness of Piedmont (approximately 50 cm/year) and the pluviometric moderation of the buttresses (100 cm in Sierra of Guara), while the interior mountain is copiously, though irregularly, sprinkled (125 cm with Benas and up to 160 cm in the Western valleys of Gallego and Canfranc). More in the east finally, and while remaining dominating, the flow of west-south-west loses in activity (80 cm with Esterri d' Aneu, 96 cm in Andorre, 60 cm in Cerdagne - high basin surrounded by protective solid masses).
Partout the high frontier chain pushes back the moderate oceanic air of the North-West, reinforcing the annual thermal amplitude which borders 15° and induced winters as cold as in France (isothermal 0° around 1250 m in January). The summers are definitely hotter (isotherm 10° around 2150 m in July). Winter snowing up is durable above 1500 mètres.
Végétation of transition: the highest valleys are still rather green and shelter beeches and fir trees locally, but only a few kilometers towards the south allow the scrubland and the maquis to impose itself (pines, holm oaks).
the Eastern Pyrenees free-Catalan women of the Aude to the Albères and of Albères with Cadi (Mediterranean Climate with continental tendency): it is the part climatically most heterogeneous of the chain. The disturbances of west-south-west and more still those of north-north-west, are weakened. The first still appreciably affect the Sierra of Cadi then decline on the Puigmal, the Canigou, the Madrès.
Inversement the seconds touch the Veined ones and Canigou, but almost not Cadi; moreover the stop of the chain towards the east partly defuses the effect of accumulation against the relief. The wind (Tramontana), finding a passage there, is often violent.
the disturbances of origin Mediterranean or southernmost, though much rarer and very random in their demonstrations from one slope to another, are particularly active in the south of Canigou (Vallée of Tech, area of Olot) where one collects the annual office pluralities most important (Swift 129 cm, Nuria 110 cm). The Vallée of the Small fireclay cup is much drier (Prades 54 cm, Mont Louis 78 cm). The temperatures are about identical to that of southern Medium mountains, except for the Chain of Albères close to the sea where the annual amplitude decrease (softer winters, fresher summers). Winter snowing up is durable above 1500 mètres.
Mediterranean Végétation (Garrigue, Holm oak, pine), punctuated of beeches in the wettest places.
central High mountain Franco-Spanish, of Ossau to the Carlit above 2000 meters (cold climate suboceanic): exposed in a dominating way to the disturbances of west in south-west (except for the peak enters the Ariège and the Val of Aran, and the surroundings of the Pic of the South of more exposed Bigorre to the north-north-west because of their position in withdrawal of the high chain).
the pluviometric office pluralities, primarily in the form of snow, are rather homogeneous from one solid mass to another in spite of a light decline of west in is (from 200 to 150 cm/year). Balaïtous is probably the “3000” more arrosé.
the thermal amplitude is moderated, of 13 with 14° (isothermal - 5° around 2200 meters in January/February, isotherm + 5° around 2800 meters in July /août).
the snowy coat around 2000 meters is generally established in November and dislocates in April.
Of the residual glaciers occupies the accesses of the more high summits: Balaïtous, Vignemale, Mount Lost, Posets, Luchonnais, Aneto. They will have probably disappeared at the end of the century, under the effect of the climate warming started since the medium of 19th. For this time they have often regressed several hundreds of meters as testify some the closest moraines. They also lose in thickness and sometimes are hidden under falls (Canigou, Besiberri, Cambalès…). Minimal altitude to allow the formation of ice goes from 2500 to 3200 meters while pouring northern, it is a little lower in the western half of the chain (which shelters the majority of the glaciers), except in half is with the Mount Valier (Ariège) which only culminate around 2800 meters and present of the small seracs under its north-eastern cliff at the exceptionally favorable configuration. The glaciers are quasi absent from slopes sud.
the high limit of the forest varies from 2000 to 2500 meters (Pin with hooks, Bouleaux).

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