You have probably heard the expression, "Red sky at night, shepherd's delight; red sky in the morning, shepherd's warning." This suggests that if there is a red sunset then the following day will bring fine weather, whereas if the dawn is accompanied by a red sky then the day will not be very pleasant.

Then there is the saying, "The north wind doth blow and we shall have snow." This is not always true, of course, but it does indicate quite correctly that bad weather often accompanies a wind from the north.

If you see a halo around the moon on a clear night this is said to be an infallible sign that there is wet weather to come. Of course, in Britain and Europe, this is very likely to be true because the weather is so variable anyway. In fact, the halo around the moon occurs when there is a certain type of cloud present that often precedes rain.

If you see a halo around the moon, it is caused by ice crystals in the upper atmosphere. The ice refracts the light and you get a mini-rainbow, but since it is night, you normally only see a whitish-yellow ring. On rare occasions, you can see two bright spots on the halo. These are called Moon Dogs.

The "Red sky at night..." expression, more commonly delivered in a nautical vein - "...sailor's delight; red sky at morning, sailors take warning" is actually based somewhat in fact, at least in the tropical latitudes where Trade Winds blow (and sailors used to ply their trade).

The "red sky" typically appears when the sun is low on the horizon shining light up onto the underside of a broad cloud deck, as one finds in storm systems. Since the Trade Winds blow roughly from east to west and the sun rises in the east, a red sky at morning means there is likely a storm upwind of one's location, and it will arrive before too long.

Conversely, a red sky to the west, where the sun is setting indicates that either a storm system has passed or one that has developed will be moving away.

Pretty much the reverse applies in the mid-latitudes, about 30-50 degrees north or south (United States, Southern Europe, China, Argentina), where the wind blows from the west (westerlies).

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