Teresa,

Snow, as precipitation, is not so much a sign of purification, but fallen snow, by virtue of its color, is in the Bible, a symbol of purity and righteousness.

• For example, in the Transfiguration, Jesus's clothing is said to be as white as snow.
  (Matthew 28:3).
• In Revelation 1:14 it says of Jesus, His Head and His Hair were white as white wool, white as snow.
• Isaiah 1:18 (RSV2CE) is another example: Come now, let us reason together, says the LORD: though your sins are like scarlet, they shall be as white as snow; though they are red like crimson, they shall become like wool.
• Daniel 7:9 (RSV2CE) says, As I looked, thrones were placed and one that was ancient of days took his seat; His clothing was white as snow, and the Hair of His Head like pure wool.
• However, snow is also a sign of impurity, in virtue of its association with leprosy.
  (See Exodus 4:6, Numbers 12:10, 2 Kings 5:27).
  
  Note: Bible passages may not match the proper translation.

So saying something like Gee, it's snowing; God must be purifying the land — would not really be consistent with biblical images, but if you were to say, After I go to Confession, I feel as pure as the driven snow. — that would be more consistent.

Eric