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 Rh\u00f4ne valley west of Brig, the strength of the breeze at 2000m is significant relative to paraglider trim speed.<\/p>\n The diagram below shows a typical evolution of the normal breeze in the main Rh\u00f4ne valley at ground level on a thermic day without any large-scale airflows. \u201cGeschwindigkeit\u201d and \u201cMittelwind\u201d refer to the average speed and \u201cB\u00f6enspitzen\u201d to gusts, showing how it often blows at 30-40km\/hr in the afternoon, frequently with peaks exceeding 50km\/hr.<\/p>\n Typical valley breeze at Visp<\/p><\/div>\n The header image (available in higher resolution here<\/a>) 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.\u00a0 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<\/a>.\u00a0 However, it\u2019s rare that the meteo wind is so weak that it doesn\u2019t 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:<\/p>\n Bise (blue)<\/a><\/span><\/p>\n North-westerly (green)<\/a><\/span><\/p>\n South-westerly (red)<\/a><\/span><\/p>\n And (in case you\u2019re planning a flight over the passes) here\u2019s 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):<\/p>\n 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 atmospheric pressure (“overpressure<\/a>“) across the Swiss Alps in the north\/south axis, which you can find at Profiwetter<\/a>.\u00a0 The values for pressure differences in more axes can be found at Windundwetter<\/a>.\u00a0 These help to predict the tendency of either F\u00f6hn<\/a> or north winds and Bise<\/a> to develop.\u00a0 Significantly higher pressure in the south is associated with F\u00f6hn, and to the north-east with Bise. If the north-south 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.\u00a0 However, I have enjoyed a couple of flights in October when the charts showed 7-8 hPa of north overpressure at ground level, in which I encountered no turbulence at all.<\/p>\n","protected":false},"excerpt":{"rendered":" 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 … Continue reading ![\"\"](\"https:\/\/www.flyfiesch.com\/wp-content\/uploads\/2017\/09\/Vwind10a.jpg\")
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