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 may hope that the meteo winds will be as light as possible, to reduce the risk of lee effects and the amplification of valley flows, but in practice their strength and direction will nearly always have a significant influence on the character of the conditions, and which options will work better or should be avoided.

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.

The diagram below shows a typical evolution of the normal breeze in the main Rhône valley at ground level on a thermic day without any large-scale airflows. “Geschwindigkeit” and “Mittelwind” refer to the average speed and “Böenspitzen” to peak gusts, showing how it often blows at 30-40km/hr in the afternoon, often with gusts exceeding 50km/hr.

Typical valley breeze at Visp

The header image (available in higher resolution here) is often referred to as the “alpine pump” and shows the expected 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 Grimseler.  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, another essential factor to take into account in addition to the wind forecasts is the predicted difference in air pressure across the Swiss Alps in the north/south axis, which you can find at Profiwetter.  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 Windundwetter.  These help to predict the tendency of Föhn or north winds and Bise to develop.  Significantly higher pressure in the south is associated with Föhn, and to the north-east with Bise. If the N/S figure is over 4 hPa in any direction, something nasty will probably be lurking in the area, such as generally choppy conditions, localised 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.  However, I have enjoyed a couple of flights in October with 7-8 hPa of north overpressure in which I encountered no turbulence at all.