We had a great time at this year’s IAS at Stoneleigh Park and met a lot of very nice people who asked us lots of questions.
A common question for us was how does the weather on the mountain differ throughout the year? Well, here is the monthly average data from the Observatory site at Izana at 2367m altitude. Minimum average monthly temperatures range between 0.9 degrees C in January to 14 degrees C in July/August.
Wind chill is always factor that can make temperatures feel lower and here is the last 12 months of daily average wind speeds. These are measured at the observatory site which is very exposed. The yearly average recorded was 12Km/h.
The other question was about cloud cover. We were quoting a yearly average of about 80% or 292 days per year and I’m sure a few people may have thought we might be exaggerating slightly. Our information isn’t anecdotal, it is from data published by the Institute of Astronomy of the Canaries (IAC) – An extract from the report follows:
We have exploited the European Climate Assessment & Dataset series of day time oktas of cloud cover at Izaña Observatory, Tenerife (Spain), to estimate the useful time at Teide Observatory. The data cover a period of 68 years (1933–2000). The useful time, considered as the sum of days classiﬁed as clear and partially cloudy, ranges between 94% in summer and 69% in autumn, with an average value of 81%. The clearest month is July and the cloudiest is November.
The clearest months unsurprisingly are in the summer but even the poorest month, November manages 20 useful days (plus or minus 6 days) which is probably better than the best month in the UK (whichever that is!).
Another reason why Tenerife is probably the best dark sky location in Europe!