Arosa in January - (strong) winds in Chur

The wx this months permitted only 2 flights to Chur (4. / 6. January) and -until I'll leave with Ruth for the Canary Islands on 22.1. - it's not looking like that there will be many more opportunities :-((

4.1. uneventful sledder...

6.1. lots of pilots on the Weisshorn; 4 of them flying to Chur...

Shortly before launching we had checked the wind in Chur and it showed little NE- (= valley) wind (around 10kmh). But when approaching Maladers, a check on my Skytraxx told me that the wind had increased to NE/ 25-37! On half-speed bar my ground speed has been as low as 5kmh at times... Luckily I've been rather high so reaching my planned landing field in Masans posed no problem and I've always had several alternative options. But some other pilots, which had arrived lower, barely reached a decent LZ...

So what had happened?

Urs (one of the pilots who had flown to Chur with me) posed this question to the Swiss Meteorological Service (Meteo Swiss), as we had not encountered this phenomenon before.

Good day

During a paragliding flight from the Arosa Weisshorn to Chur, we were surprised by a weather phenomenon that put us in a dangerous situation and which I absolutely cannot understand. I would be very grateful if you could comment on this.

On 06 January 2023 in the afternoon, generally weak winds were forecast. This was also the case on the summit of the Weisshorn and over the entire Schanfigg. Over Chur, at about 1415 hrs, we were suddenly caught by a strong gusty wind from the north-east (valley wind), which, according to our navigation equipment, was a good 40 km/h. This meant that we were practically at a standstill against the wind and with a lot of luck we were able to land unharmed at various emergency landing sites. The strong wind continued for about 20 minutes after the landing, after which it was practically windless, as it had been before.

Questions: How could such a sudden strong wind occur in this low wind situation without a shower or change in the weather? How could I recognise such a danger at an early stage in the future?

Thank you very much for your valuable assessment

Kind regards

and that's the answer he received:

Good afternoon

 

On this day there was widespread high fog over the Central Plateau with an upper limit of around 1300 m to 1600 m. In the foothills of the Alps and the Inner Alps it was sunny. In the Pre-Alps and Inner Alps it was sunny.

The different levels of insolation ensured that a pressure gradient was able to build up in the Rhine valley. The pressure gradient was of course further favoured by the lack of snow cover.

At the indicated time, gusts of 21 knots were measured in Chur. The pressure gradient then decreased again in the course of the afternoon. Varying solar radiation can also cause such small-scale wind phenomena again and again in the winter half-year.

 

With kind regards

MeteoSwiss

> I'm very happy, that the Skytraxx is able to show almost in real-time such wind information. Thus I've been 'warned' early enough about this possible danger and could plan accordingly.

> also many thanks to Urs for getting this information!