Nephelai

The Nephelai (or Nephelae) were the Naiad nymphs of clouds and rain who rose up from the earth-encircling river Okeanos bearing water to the heavens in cloudy pitchers. With their rains, the Nephelai nourished the earth and the fed the streams of their River-god brothers. The Nephelai were depicted as beautiful, young women pouring water from pitchers, like their sisters, the Naiades of the springs, or as women flitting across the sky with billowing robes.

The cloud nymphs tended to be the younger of the Okeanides which is why many Nephelai such as Hyalê and Nephele were among the maidens who were part of Artemis' hunting party.  This however is not always the case, Okeanis had two Nepheai named Nephele, one was a follower of Artemis the other married a mortal (King Athamas).