Wind patterns

An understanding of the wind patterns around Fiesch and further afield is the key to safe, enjoyable flying here. In such big mountains, one hopes that the meteo winds will be light. However, their strength and direction will always have a dominant influence on the character of the conditions and therefore flight planning.

The header image (available in higher resolution here) shows the expected lower level winds on a thermic day in the summer, when unaffected by any significant large-scale flows.  The black arrows represent the normal valley currents, the blue arrows indicate upslope flows, and the red arrows show descending winds, such as the Grimselschlange.

The following four images show a typical evolution of the valley flows to be expected around 2000m over the course of the day, when there is no significant meteo wind:

Note that even at 16:00 the winds are still weak around Fiesch, but at the upper end of the Goms and in the main Rhône valley west of Brig, the strength of the breeze at 2000m is significant relative to paraglider trim speed. However, it’s rare that the meteo wind is so weak that it doesn’t amplify, inhibit, or even reverse the usual valley flows. So the diagram below shows the airflows to be expected in the three most frequently encountered meteorological wind conditions:

Bise (blue)

North-westerly (green)

South-westerly (red)

And (in case you’re planning a flight over the passes) here’s a similar diagram, produced by the local club in the Surselva, showing the expected airflows there in more detail than in my chart, with the same colour coding (blue for Bise, green for north-westerly, and red for south-westerly meteo winds):

When assessing the prospects for the day, an essential factor to take into account is the predicted difference in air pressure across the Swiss Alps in the north/south axis, which you can find at Meteocentrale.  I use the terms north and south overpressure throughout this site to refer to this parameter.  The values for pressure differences in more axes can be found at Flugbasis.  These help to predict the risk of Föhn and Bise.   Significantly higher pressure in the south is associated with Föhn, and to the north-east with Bise. If the figure is over 4 hPa in any direction, something nasty will probably be lurking in the area, such as general turbulence, strong flows of air from unexpected directions, wind shears, or big slabs of strong lift or sink. Even 2 hPa, especially if early in the season, can produce a surprise or two.