In the Synaxarion for November 6th, together with the Saints who are celebrated that day, it also states: "On this day we remember the ashes falling during the reign of Leo the Great".
The Stichos for the feast says: "You threatened to burn us, but we did not burn, since You mingled Your anger with long-suffering O Word".
The explanation for the feast in the Synaxarion of Constantinople, reads:
"In the eighteenth year of Emperor Leo the Great [472 AD] on November 6, in the afternoon hours, the entire sky [of Constantinople] was filled not only with the common black clouds, but with clouds as red as fire. All were amazed and feared that flames of fire would fall, burning them like Sodom. The people ran to the churches and prayed with tears and lamentation.
But the God who loves mankind tempered His punishment with His love and in the evening it began to rain until midnight. The rain brought down dust that was black as ash and covered the earth and houses more than an inch. All the crops and grass and trees of the earth were burned. It was not easy to unstick this dust with water, and thereby the anger of God was revealed for our sins.
The following days many heavy rains fell and the dust was washed away. This means that our sins are like red and black dust on us and it eats away our every virtue, and like the rain many tears are needed and much repentance for us to be washed of the hot ashes of our sins. And when the evil ashes are washed away, let us water the good earth of our nous to bring forth fruit-bearing virtues. In this way we will escape the punishment of hell which will burn our bodies and souls, and gain the Kingdom of Heaven."
This then was the event, the unusual weather phenomenon which the historian Procopius and the Synaxaria portray with such horrifying colors, that it caused the people to interpret this as the wrath of God for the sins of mankind. It was a justifiable anger that would have burned everything, eventually however God's love for mankind, the long suffering of Christ, changed the fire to a warm ash that eventually washed away and left.
The incident must have been so horrifying for the Church at the time to celebrate this event every year. And on the Sunday between October 30th and November 5th it has been established that the Parable of the Rich Man and Lazarus be read which speaks of the other life, of our repentance, and of the terrible fires of hell and punishment of sinners. From one historical, meteorological event, the Church reminds the faithful of our salvation.
It was the eruption of Vesuvius on 5-6 November 472 which brought the clouds with the warm ashes to Constantinople that created this horrifying incident mentioned in the Menaion of November, in which the relationship between spiritual laws and natural laws are taught, as they were established by God and given to man.