Tomorrow begins the autumn Ember Days. According to New Advent, "Ember days (corruption from Lat. Quatuor Tempora, four times) are the days at the beginning of the seasons ordered by the Church as days of fast and abstinence." The autumn Ember Days begin after the Feast of the Exaltation of the Cross, which was September 14.
The Church instituted Ember Days early in her history. Pope Leo the Great believed that three of the four sets of Ember Days had been instituted by the Apostles. Ember Days are characterized by fasting and half abstinence for the purpose of thankfulness for God's gifts of nature and to direct us toward moderation and almsgiving.
According to Fisheaters.com, "Ember Days are days favored for priestly ordinations, prayer for priests, first Communions, almsgiving and other penitential and charitable acts, and prayer for the souls in Purgatory. Note that medieval lore says that during Embertides, the souls in Purgatory are allowed to appear visibly to those on earth who pray for them.
Because of the days' focus on nature, they are also traditional times for women to pray for children and safe deliveries."
According to folklore, tomorrow's Whit Embertide will foretell October's weather. :-)
Read about this week's Ember Days (Wednesday, Friday, Saturday) here. Here's an article about Ember Days in the 21st century at the National Catholic Reporter. H/t to Fr. Z, who also writes about Ember Days today.