Possible Clues:

• It's high in Washington
• Prince formerly with his purple stuff? That's right
• Washington stratovolcano
• Seattle, comparatively
• Comparatively wet ruler of principality
• Noted Mount or Monégasque
• Wetter, weatherwise
• This is more likely to pour down volcano
• Peak in Washington providing more drops?
• Only so-called 'Decade Volcano' in the continental U.S