{"id":2946,"date":"2018-11-11T14:46:22","date_gmt":"2018-11-11T14:46:22","guid":{"rendered":"http:\/\/flyfiesch.co.nf\/?page_id=2946"},"modified":"2023-05-07T14:47:20","modified_gmt":"2023-05-07T14:47:20","slug":"fohn-case-study","status":"publish","type":"page","link":"https:\/\/www.flyfiesch.com\/?page_id=2946","title":{"rendered":"F\u00f6hn case study"},"content":{"rendered":"

I decided not to go to Fiesch on 13th October 2018, as the weather forecasts indicated too high a risk of f\u00f6hn as far as I was concerned.\u00a0 These are the charts showing the information on which I based that decision, and how things actually turned out:-<\/span><\/p>\n

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UK Met Office synoptic chart for 12:00 UTC<\/p><\/div>\n

That degree of spacing between the isobars would normally be associated with a general meteo wind of noticeable but not uncomfortable strength in the high mountains. However, the pair of cold fronts approaching from the Atlantic rings an alarm bell, even though the chart shows them as not having even reached the French coast by the middle of the day.<\/p>\n

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Meteocentrale Z\u00fcrich-Lugano pressure difference chart<\/p><\/div>\n

The north-south pressure difference chart shows borderline values for 13.10.18 \u2013 an increase from 2 to 4 hPa over the course of the flyable part of the day.<\/p>\n

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Flugbasis chart of winds at 3000m at 13:00<\/p><\/div>\n

The Flugbasis chart (sadly no longer available) predicts a very light southerly at 3000m in the Goms, albeit with some funnelling through the Grimsel pass (no Grimseler<\/a>!).\u00a0 The easterly in the main Rh\u00f4ne<\/span> valley may only be around 13km\/hr, but it\u2019s blowing the \u201cwrong\u201d way (i.e. downwards).<\/p>\n

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Flugbasis chart of winds at 2000m at 13:00<\/p><\/div>\n

However, the chart for 2000m is ugly! Although the Goms looks ok, winds around 24km\/hr to the south-east of Fiesch, at Oberwald, and west of Brig have the potential to generate nasty conditions in those locations, and Andermatt could be quite malignant.<\/p>\n

So how did things turn out? Here are the charts (from SpotAir) for key weather stations, showing the actual values at 17:00, with the history over the preceding hours:<\/p>\n

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The key points here are<\/p>\n