There is an old adage about mountain flying, that “the windsock points in three different directions” at mountain airports. The prospect is appropriately disconcerting to a pilot that has not flown in mountains before, as a decade and a half of flatland flying in the East Coast taught me that, if the general wind for a region is from a certain direction, well, one can easily presume that it is blowing the same direction down the runway. Any mental gymnastics as to what could be going on to create swirling winds was not necessary at the time, and therefore was relegated to the age-old heap of reasons to be afraid of mountains.
My first landing in Leadville, Colorado, after crossing Tennessee Pass in snow showers was as advertised. Winds were in three directions as foretold, so I picked something just over the numbers, did the stick and rudder dance, and got the airplane on the runway as though death was the only other option. Then I had to taxi a half mile, noting that the wind really wasn’t that bad.
A few hundred hours of flying in Utah, Wyoming, Colorado, Idaho, and Montana confirmed the maxim that the wind is “always” in three different directions. The US West features high valleys, open spaces, and lots of afternoon wind in summer, which is thermally driven. With such vertical winds, localized chinook action, and some orographic wind funnels, it seemed to be the norm to expect something on the wild side, generally not in line with a thing called a “forecast,” and I grew to deal with it.
Fast forward to Spain and La Cerdanya, which featured more hundreds of hours of flying, and it only partially validated this maxim. With an ambient north wind, enormous waves would set up, with a wind funneling out of the Val du Carol in France, before making a turn and working themselves out over the Pre-Pyrenees. On south wind days, a small wave would set up over our house, with slamming doors and windows, bent trees, and afternoon fury, with a light breeze two miles away at the airport. As one would expect, in flight the valley was interesting as the vertical ripples sorted themselves out and found a way to transit the range, though they were predictable. I wrote the experience off as “that’s mountain flying” whereas in retrospect, I would peg the winds as about half as complex as the US West.
Now enter the Alps. A rational presumption, due to the height, severity, and density of terrain would be to expect sheer carnage, with death-dealing winds swirling undetectably around phantom summits, ensnaring pilots that dare enter the range. I can attest that I thought such a thing, and within a short period of my initial adventures in Switzerland, my illusions of sheer terror were replaced with a feline skepticism of nearly everything I saw. Now that the on and off again Swiss adventures have piled up some decent experience, I can attest that presumptions about wind that work in the Rockies are not analogous here, at least when it comes to windsocks on the field.
I arrived at these conclusions by doing one of my “its dark, I’m playing with my computer, and I can’t go flying” exercises, tallying up total landings at various home base airports. When I added up my experiences at three different Swiss “home” base airports, I came up with some very interesting conclusions:
Sion – 16 landings – 100% on runway 25
Bex – 21 landings – 100% on runway 33
Saanen – 33 landings – 91% on runway 26
Samedan – 3 landings – 100% on runway 21
In deeper consideration, I can’t recall a “crosswind” of more than 20 degrees at any of these airports on any of these 73 landings!
One has to ask, if “the windsocks are blowing in three different directions in the mountains,” how the wind is always in one direction? In the Alps, the answer is pretty simple: aside from the reality that windsocks usually are in agreement, terrain is so steep and with such vertical relief that wind channels are formed in terrain. A prevailing crosswind can be blowing at an upper level; however, with a valley a mile or less wide yet 20 miles long, with a mile or more of steep terrain acting like walls, is it really going to rush down 5000 feet, cross the runway, rush up another 5000 feet, and keep going? Winds tend to form channels that find the path of least resistance, turning left and right down steep and long valleys until reaching a pass or relief point, where the pressure can equalize by having the wind roar over a small area to the other side. In fact, passes with towering terrain often have the strongest wind, with more relaxed breezes blowing on summits above the pass. This means that sometimes the wind turns 90 degrees or more relative to general flow down in the valleys, while maintaining a single direction above the summits.
I encountered this reality a bit in the Tetons. Instead of arcing over the Tetons with a resounding fury, rancorous rotors, and a slew of mystery, the wind most of the time just blew around them. In Glacier National Park, with 30 knots of winds at summit level, the same thing happened: winds funneled like the Alps, left and right as they found channels to get to the other side. While there are similarities, I can attest that my limited experiences of the sort in the US were nowhere near as pronounced as the uniqueness of the Alps.
Here are some photos of airports to demonstrate how terrain works:
Bex, Switzerland – The airport is halfway to the horizon. One can understand why the winds are virtually always blowing from the north (toward me in the image). Below is Martigny, which is typically quite raucous as three major wind currents converge and head east to Sion.
Just north of Sion, looking east. The previous image was taken 10 miles behind me. The Rhône Valley continues for another 30 miles, meaning that winds blow most of the time west to east down the valley.
Saanen, taken north of the field, looking west. Terrain to my right, out of the image, is about as high as the left, meaning that winds blow down the valley 91% of the time (at least for me), favoring 26 unless there is a strong post-frontal northeast wind event, for which the reverse occurs.
Samedan. What is evident at this point is that I don’t have good shots of the whole airport of any of these places. That likely has to do with the fact that I do not turn the airplane 90 degrees on final to get a wide photo of what is going on. Nonetheless, the terrain that is on the other side of the airport is mirrored just behind me as I am painfully close to the trees on the right while on downwind. This valley configuration is at least 20 miles long, meaning relatively consistent wind patterns.
In separate news, book #23 is published: Mountain Texture: Glaciers of the Alps. Like my three prior aerial texture works, it features close up perspectives of the many textures and details of glaciers found in Italy, France, and Switzerland.