The Sierra de Guadarrama, along with the Gredos and Ayllón Sierras, makes up the Sistema Central (the Central System). This chain of mountains runs basically in West-East direction and splits the meseta in two subplateaux having different continental mediterranean climates. The orography of the Central System has a direct influence on the Iberian Peninsula climate; the Northern area has a temperate climate, with dry and warm summers (Csb according to Köppen climate classification) and the Southern region has dry and hot summers (Csa). Csb climate is the one dominating in the Sierra de Guadarrama.
This continental mediterranean climate, typical of the peninsular interior, overlaps in the Sierra de Guadarrama with the mountain climate, with very cold winters and dry chilly summers. As the height increases, there is a precipitation and temperature gradient across the Sierra, so precipitation is more copious and, generally, in the form of snow. On the other hand, the temperature varies inversely to the height.
Another important feature of the Sierra de Guadarrama consists of a bold continentality, in other words, a great temperature contrast. The combination between this quality, the variability caused by the topography (the elevation, slope, orientation and modelling of the Montes Carpetanos and Cuerda Larga alter the air flows), and the distance both to the Atlantic Ocean and to the Mediterranean Sea, makes the Guadarrama area a mosaic of climatic regions. At the same time, these climatic regions influence the existing vegetation patterns and the fauna.
The major example on how the climate influences the landscape in the Guadarrama area is the geomorphology subsequent to current periglacial processes. Similarly, glacial processes (occurred thousand years ago) in the Peñalara massif have created the circuses, moraines and high mountain lakes.
For greater precision, the climatology of the Sierra de Guadarrama National Park can be illustrated with the historical data observed at the AEMET meteorological station in the Navacerrada Pass (Puerto de Navacerrada), located 1890m height. It is a very cold and temperate summer Mediterranean climate, with -0.4 ºC and 17.0 ºC average temperatures on coldest and warmer month, respectively January and July. The annual average precipitation is 1.223 mm, being 27 mm in July and 176 mm in November, and can be described as strongly mediterranean. The annual average amount of snowfall days is 71, while the one for frost days is 136.
T Average monthly / annual temperature (°C); TM Monthly / annual average of the maximum daily temperatures (°C); Tm Monthly / annual average of minimum daily temperatures (°C); R Average monthly / annual precipitation (mm); H Average relative humidity (%); DR Monthly / annual average number of days of precipitation greater than or equal to 1 mm; DN Average monthly / annual number of days of snow; DT Monthly / annual average number of storm days; DF Monthly / annual average number of fog days; DH Monthly / annual average number of frost days; DD Monthly average annual number of clear days; I Average monthly / annual number of hours of sun
As it can be seen in the Navacerrada Pass climatogram, there is a moderate period of aridity during the months of July and August. This is typical of the Mediterranean climate, although the influence of mountain climate makes the season cooler and more humid. The annual thermal oscillation is 17.1 ºC, between the months of January and July. The vegetative period is 5 months, except in the peaks higher from 2.000m, in which it is shorter.
The temperature gradient (ºC / 100 meters) in the Navacerrada Pass and Segovia (1.005 m height a.s.l.) AEMET stations has been calculated. Although there are fluctuations depending on the month and the year of reference, the average goes from 0,50 to 0,72 ºC in November and April, respectively. A negative gradient about 0,62 ºC/100 km is observed.