04-12-2015
A dry November…and now what?
Facts
The last part of the fall was indeed the best time of the 2015 summer season. Stable weather, plenty of sunshine and above average temperatures that lasted almost throughout November. This meteorological pattern of high-pressure and consequently stable weather kept the clouds low in the valleys, so that everyone that had the chance to climb on the mountain in October and November had a sort of a “divine” feeling of being above the clouds and the problems of the lowlands. The photography of Vasilis Triantafyllou provides the most reliable evidence of how the “summer/fall” season on Mount Olympus concluded.
Panoramic view of “Divine Olympus” by Vasilis Triantafyllou.
Philosophy
The “official” conclusion of the 2015 summer/fall season (that means when the muleteers have taken their mules down and when the refuges have closed down for good) took place in early November and the semi-permanent inhabitants (the refuge managers and their colleagues) left the place to the permanent inhabitants; the wild chamois and the rest of the fauna, the flora, the rocks and the most important the Gods. In other words they gave the mountain the well-deserved opportunity to retune to its own loneliness, peace and to balance back to its natural rhythm. But mortals are greedy and always want more, so they are expecting to come back for another “good” winter in terms of snowfall and activities (mountaineering, ski touring and splitboarding, etc.).
Photos by Vasilis Triantafyllou
Turning the monologue from philosophical to scientific and looking back to 2015, when we experienced a good (heavy) winter, a warm spring, a very wet and cold early summer that after late June turned into a “normal” summer that ultimately gave space to a very dry fall and early winter, I became increasingly conspicuous about “what does a dry November may bring?
Photos by Vasilis Triantafyllou
Climate Science
Usually November is rainy in the valleys and snowy on Mount Olympus, but looking back to climatological data from 1950 to 2010 it appears that there have been many dry Novembers in the past as well. Scientific analyses show that most (about 60%) of the rain that hits the Mount Olympus region in winter is related to the North Atlantic Oscillation (NAO), an irregular climatic phenomenon that controls the strength of the westerlies (west winds) over the north Atlantic and much of Mediterranean Sea. It is expressed by the NAO Index, the difference in atmospheric sea-level pressure between Iceland and the Azores (http://www.ldeo.columbia.edu/res/pi/NAO/). For Mount Olympus negative winter NAO Index values are related to lots of rain and lots of snow on the mountain. Positive NAO Index are related to poor/dry winters. Unfortunately this winter we are in positive NAO phase. But mind you, in many years after a dry November and while NAO Index had positive (>0) values, the winter turned to be extremely wet (look in the following figure) so things can be different from what they look so far.
Photo by Vasilis Triantafyllou
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In this figure the winter NAO Index is shown against winter rainfall (data are from Katerini town, a city located in the lowlands 30km northeast from Mount Olympus) for the years of the record when November had less than 20mm total rain. If you take a close look to the horizontal axis you will see that some winters with dry November and positive winter NAO Index turned out to be very wet, like the 1972/73, 1973/74, 1997/98 winters, with the most recent one being the winter of 2002/2003.
Photo by Vasilis Triantafyllou
Of course the North Atlantic Oscillation pattern is not the only climatic phenomenon that influences the rain/snow on Mount Olympus. Climate is very complex and there are many parameters that influence winter rain and snow on every corner of the planet. This year we also have a strong El Nino in tropical Pacific Ocean and climatologists are puzzled of what this winter will bring, so if you have not been tired of the above analyses take a look what the experts say.
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http://www.jpl.nasa.gov/news/news.php?release=2015-352
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http://www.gavsweathervids.com/winter2015-16-forecast-uk.php
Best Wishes for an “active” winter.
MS
