If you filter the flights on this XContest page by date, you will find flights using thermals made from Fiesch at all times of year.  You can use this extraordinary search facility to drill down into specific periods in previous years, to view hard data on the variability of the conditions and estimate the probability of encountering a five star day or unflyable intervals at a particular time.

In November, December and January, it is rare – but not impossible – for conditions to be good enough to clock up much distance.  The first substantial XCs of the season usually begin to appear in February.  In March, it may be flyable on about one day in three, of which half may provide conditions enabling good pilots to achieve 100km flat triangles.  In April, the frequency of days when it’s pleasant to fly is much the same, but a few are likely to provide superb conditions: the header image was taken in April 2013 as I started the transition from Eggishorn towards Bellwald, showing a cloud street marking a line of regular 2-3m/s thermals releasing from the snow line to base at around 3,000m, along the valley.

May can be exciting – some say “brutal” – due to the combination of strong solar heating and a brisk lapse rate, and usually includes a couple of days with conditions enabling flights over 300km, but the weather is often quite fickle then, and the uphill transport may be closed for maintenance or on a severely restricted schedule from the closing of the ski season until the end of that month.  In that case, you can use the takeoff at Riederalp, about 8km to the west, accessed by the gondola from Mörel.  In June, you can usually expect plenty of good days, but the thermals are likely to have sharper edges and the frequency of unsettled weather is higher than later in the season.

In my opinion, the best month to choose to fly in Fiesch is July, due to the likely maximum frequency of good days. The really classic conditions with cloudbase at 4,000m tend to occur in August, but there is also a greater chance of stability and inversions then. September often provides a mixture of mellow and lively conditions, with plenty of big XC days, but by October these are rare, and the tendency to weather disturbances in the Alps in the autumn can produce an unacceptable frequency of non-flyable weeks.

Here are a few of my flights from outside the normal season:

February flight (click here for XContest details)

October flight (click here for XContest details)

December flight (click here for XContest details)