We experienced a relatively unusual meteorological phenomenon on the Aberfeldy to Acharn walk I led on Saturday for the Drovers’ Tryst walking festival – a fog bow. This glowed as we climbed through the upper layers of the cloud filling Strath Tay, caused by a temperature inversion that trapped cold, moist air below a warmer, drier atmosphere. These conditions occur most often in autumn.
Like a rainbow, a fog bow is seen on the opposite side of the sky from the sun. However it is white rather than multi-coloured. You need to be still within the fog, but high enough to be catching some of the sun’s rays – once above the fog you lose the effect, but may be lucky enough to see a Brocken spectre. We weren’t treated to one but we did have glorious views over the cloud bank.
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