MYTH: When rainbows cease to be seen on the earth the second coming of the Savior will be near.
POSSIBLELY TRUE BUT UNPROVEN
It’s a long held belief in Mormon culture that a lack of rainbows is a sign that the Second Coming will be imminent. This belief is actually less myth than prophecy, and as such it cannot be tested, but it’s worth examining the origins of this prophecy.
After the great flood as recorded in Genesis, God created a rainbow in the sky as a promise to Noah, and all the creatures of the earth, that he would never destroy the whole earth again by flooding it. The book of Genesis records:
And I will establish my covenant with you; neither shall all flesh be cut off any more by the waters of a flood; neither shall there any more be a flood to destroy the earth.
And God said, This is the token of the covenant which I make between me and you and every living creature that is with you, for perpetual generations:
I do set my bow in the cloud, and it shall be for a token of a covenant between me and the earth.
And it shall come to pass, when I bring a cloud over the earth, that the bow shall be seen in the cloud:
And I will remember my covenant, which is between me and you and every living creature of all flesh; and the waters shall no more become a flood to destroy all flesh.
And the bow shall be in the cloud; and I will look upon it, that I may remember the everlasting covenant between God and every living creature of all flesh that is upon the earth.
And God said unto Noah, This is the token of the covenant, which I have established between me and all flesh that is upon the earth.
Former president of the LDS Church, Howard W. Hunter stated:
The Lord made a covenant with Noah, and the rainbow became the token of that eternal covenant with all mankind (see Genesis 9:13).
Joseph Smith taught that there was a greater significance to the appearance, or lack, of a rainbow. While seeing rainbows was a perpetual reminder of God’s covenant to never again destroy the earth, the disappearance of rainbows hailed the coming of the end. Smith prophesied:
The Lord hath set the bow in the cloud for a sign that while it shall be seen, seed time and harvest, summer and winter shall not fail; but when it shall disappear, woe to that generation, for behold the end cometh quickly.
Joseph Smith later confirmed this prophecy and expounded on what the “end” meant.
I have asked of the Lord concerning His coming; and while asking the Lord, He gave a sign and said, “In the days of Noah I set a bow in the heavens as a sign and token that in any year that the bow should be seen the Lord would not come; but there should be seed time and harvest during that year: but whenever you see the bow withdrawn, it shall be token that there shall be famine, pestilence, and great distress among the nations, and that the coming of the Messiah is not far distant.
This prophecy has been embraced and repeated among members of the LDS Church who make it a point to monitor and study the signs of the times. LDS author Roger K. Young stated, “For example, one of the signs warning us that the time of His Coming will be within a year is the absence of rainbows.”
So this myth proves to have historical relevance and only time will tell if Joseph Smith’s prophecy proves true.
 KJV Bible, Genesis 9: 11-17
 Howard W. Hunter, “Commitment to God,” Ensign, Sep 2006, 44–47
 History of the Church, Joseph Smith. Volume 5, p.402
 Ibid, Volume 6, p.254
 Roger K. Young, “..As a Thief in the Night..” Celestial Publications and Distribution, American Fork, UT 1999, p.4