Winter’s Back, and a look back to Winter.
5th April 2021
A histogram of the air temperature at 1100 metres on Aonach Mor in 1 degree Celsius bins. The data shows the 2160 hourly temperatures where taken between the 1st of January and the 31st of March. Both the mean and median values are -2.4°C. The lowest was -11.4°C, and the temperature was below 0°C about 75% of the time. It was above 2°C 10% of the time, and below -7.0°C 10% of the time. The data is kindly supplied by the Scottish Association of Marine Science in Oban. It comes from a device that has been developed to monitor snow properties. The original device, called SIMBA, was designed for sea ice work, and used successfully on the likes of the MOSAiC project (that is the project a couple of winters ago when a ship froze itself into the arctic ice and drifted with the ice through the winter). In terms of application to snow, it can be used to automatically monitor conditions and snow properties in locations/at times that are too hazardous or remote for humans to access.
The table above shows the average Aonach Mor midday summit temperatures for the central three months of the avalanche season (January to March) for the past 14 years ranked in order of coldest to mildest. This year’s results are highlighted: January was the 2nd coldest, February the 4th coldest and March the 10th coldest (5th warmest). The final column is for the three months combined, this year was the 4th coldest out of last fourteen, not too bad (for modern times). The data for this chart comes from met office weather station (not the SAMS device mentioned in the previous figure or the holfuy station mentioned right at the beginning of the post) and is recorded on the daily SAIS snowpit.
The blue line in this chart shows the combined January to March temperature (the same data as in final column of the previous table) in graphical form. The orange line show the average Scotland temperature as recorded by the met office for the same period. This data comes from the met office, and can be freely downloaded from their website. As can be seen there is good correlation between the two plots over this time period. The cold winters of 2010, 2013, 2018 and 2021 show up in both, as do the mild winters of 2012 and 2017 and 2019. The advantage of the met office data is that their data set goes back a lot further, which leads on the next graph…
Looking at the whole met office data set for Scotland’s January to March temperature, the trend is generally up. Before about 1989 (about the time the SAIS started), the January to March period was rarely above 4°C, it happened about 6 times from 1885 to 1988. Since 1989 it has happened about 13 times. Of the 12 warmest January to March periods, 11 of them have happened since 1989. Given the correlation seen in the previous figure, if we had Aonach Mor summit data going back to 1885, we would see a very similar trend. On a slightly less depressing note (for someone who likes snow) this year the January to March temperature was slightly colder than average. It was +2.8°C which ranks as 65th in the 136 years dataset. I find it interesting to note that the period between about 1945 and 1965 seems to show more variability in temperature than other periods. However, it is getting a bit above my pay-grade to start commenting or speculating on thing like that, I am just a humble snow-proder who likes graphs and weather!
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