Broadly speaking, the meteorological phenomena that characterize the climate on the Cantabrian coast of the Iberian Peninsula are determined by the seasonal behavior of atmospheric variations in terms of pressure, temperature and humidity mainly.
The anticyclone of the Azores conditions the snowfall cycles in the Cantabrian coast, being the common denominator in the atmospheric composition of the two scenarios that will determine the precipitations in the form of snow in this region: Northwest and northeast.
SITUATION OF NORTHWEST
In winter, an indicator of an approaching precipitation episode in the form of snow is the precise location of an anticyclonic area in the Atlantic Ocean, off the coast of Portugal, and an area of low pressure located between France and the United Kingdom.
It is a storm area located above Central Europe and that turns counterclockwise (north hemisphere) is combined with the dextrorotatory turn of the high pressure mass located off the coast of Portugal, causing an air corridor from the polar regions that flows directly towards the Cantabrian coast of the Iberian Peninsula. This jet of very cold air is loaded with moisture as it passes through the Atlantic that discharges in the form of snow to meet the Iberian landmass.
SITUATION OF NORTHEAST
Atmospheric situations such as this caused snowfalls reminiscent of the past at the end of February 1888 and a very recent one in October 2018. These episodes maintain a common denominator with the previous ones in the form of an anticyclone off the coast of Portugal. However, in these situations a depression is representative of the Mediterranean Sea, between the Itálica Peninsula and the Iberian Peninsula, just below the alpine arch.
On the Scandinavian region an anticyclone which communicates with the Atlantic creating a jet stream that comes from Siberia and canalizad to all over the European continent reaches the Cantabrian coast of the moistened Iberian Peninsula due to its passage through the Bay of Biscay is formed and carrying the region of copious snowfall.
EFFECTS OF THE INSTABILITY ON THE SNOWPACK
This region, which includes the north of the Iberian Peninsula from its Atlantic coast to the Bay of Biscay, is included in the nivo -meteorological classification defined by McClung & Shearer [1] corresponding to the category of maritime climates. These regions are characterized by snowfalls with great precipitation and high temperatures (values close to 0°C). Due to this, deep snow deposits will form with a certain tendency to instability, since the rapid fluctuations of temperature and precipitation during the snow season usually alternate between rainy episodes and the entry of Arctic air jets, leaving new rainfall in the form of snow. This can overload the structure of the mantle and cause landslides due to the formation of unstable layers inside it.
[1] McClung, D and Shearer, P (2006) The Avalanche Handbook, The Mountaineers Books, Seattle.