Red sky at night, shepherds’ delight?

One of many bucolic sayings, it’s often assumed that ‘Red Sky at Night’ is just another rather outdated prophecy that has no actual basis as a predictor of weather. Yet out of all of them, it’s the only one that I sometimes use myself.

Our weather typically crosses us sequentially from west to east. When we look to the glowing western sky at sunset, the red part of the spectrum is being scattered towards us off high clouds – often the last trailing vestiges of a rain-bearing front.

With the front departing, we can expect a day or so of fine weather – hence the ‘shepherds’ delight’. However there is a counter-effect, which provides equal truth to the second half of the adage: “Red sky in the Morning, Shepherds’ Warning”. At dawn in the east, invading high cloud will also light the sky up red – a precursor to a new weather front, with thicker cloud and rain arriving from the west. A warning – not just to shepherds – of a wet day to come.

If only it was always that straightforward. We occasionally need supercomputers too!