Thinking back to the last snow event in Shetland - and the (possible)
forthcoming one next week - a point to bear in mind, is that in
periods of drift snow when the fine blowing snow gets inside the
screen the result is often that the dry bulb thermometer will also
became an ice-bulb. In my experienvce this can reduce the 'air'
temperature by as much as 1.5°C - ie both 'dry'bulb and ice bulb
reading more or less the same.
Wiping the bulb with a dry cloth solves this – but you only have a
short moment before it again reverts to an ice bulb again! I hate to
think what this does to readings from AWS!

Dave
Fair Isle