Sunset Season

As we move away from the Autumn Equinox and towards the Winter Solstice it seems to me that, along with the days getting shorter and colder, the evening skies are getting brighter and bolder. We often get brooding skies, with the oranges, pinks and reds from the setting sun breaking up the greys, blues and purples of clearing storm clouds to produce dramatic scenes such as one I witnessed at Castle Tioram on a late-November afternoon and shown the image below. This makes me beg the question: Are late autumn and winter sunsets better than those we get at other times of the year? Well, it turns out that scientific studies have confirmed this to be the case and they have discovered the reasons why

Image 1: Brooding: Castle Tioram, Loch Moidart, Doirlinn, Moidart

​Scientific researchers have found that the peak sunset season is from November through to February and that this is down to a combination three things. These are the type and quantity of the cloud cover, cooler air temperatures and how the Earth is tilted towards the sun at this time of the year.
 
Contrary to what you might think, we need clouds for a good sunset and they have to be the right kind of clouds. If they are too low down on the horizon, they will block out the Sun’s rays and prevent a sunset. Instead, we need mid to high level clouds that will refract the sunlight and give us those beautiful sunset colours. This happens more in autumn and winter because the weather patterns we get then tend to bring mid and high-level altocumulus, altostratus and cirrus clouds.

Image 2: Lilac & Gold - Morvern from Loch Sunart Shore, Rockpool House, Resipole, Sunart

​The cooler temperatures mean that the air is less humid and that there is less water vapour to capture dust particles that are in the air and create the haze which is often a feature of the summer months. When present, this haze scatters sunlight and reduces its intensity. So, in autumn and winter, the lower humidity means that the air is clearer and we see the colours produced by the setting sun in all their intensity.
 
Finally, as we approach the winter solstice, the North Pole gets tilted further away from the sun, lengthening the time taken for the sun to set. This, in turn, means that the sunset colours last longer than at the equinoxes, for example, when the sun sinks very quickly towards the horizon at a 90-degree angle. The result is that we have more time to enjoy the sunset colours and the sunset colours have more time to make an impact on us.

Image 3: Winter on Linnhe - Loch Linnhe from Camas Shallachain, Sallachan, Ardgour

​Despite all of these variables, predicting sunsets doesn’t have to be hard. All you need to do is keep an eye out for the following key indicators:
 
Mid to high-level clouds (2km and above)
Cloud coverage - 30 to 70 percent
Humidity - low but not too low
Clean air
Prior rainfall - no less than 2 to 6 hours before
Wind speed - low or non-existent
 
There are many online forecasts for these weather conditions and the one I refer to most is windy.com. So why don’t you have a go at predicting a sunset and head west at what you think might be a good time. You never know, you may be well rewarded for your efforts!

Image 4: Distant Light IV - Achagavel, Gleann Dubh, Morvern