How would you describe fresh clean air?

Can you describe how the moisture in a maritime polar (mP) air mass that formed other the north Pacific ocean?

• Can you describe how the moisture in a maritime polar (mP) air mass that formed other the north Pacific ocean would modify as it moved inland over the western coast of North America?

• Answer:

  mP air masses form over cold ocean currents or high latitude ocean waters. Although mP air does not have as much moisture content as mT air, it is always near saturation. When it hits the coast of North America, it is forced to rise over the terrain. The rise causes lowered pressure and temperature, and the air becomes supersaturated. The result is widespread rain or snow. MP air masses in North America are notorious for producing fog, drizzle, cloudy weather and long lasting light to moderate rain. The temperature of mP air ranges from just above freezing to below 70 degrees F. mP air is modified as it moves over elevated terrain. On the windward side of mountain ranges, mP air can produce an abundance of rain and snow. Once on the lee side of mountains, the mP air mass drops and the temperature rises. The air mass is now has much less humidity and modifies into a continental air mass. These air masses produce cold fronts but the air is not as cold as polar or arctic fronts. They are often termed "Pacific fronts" or "back-door cold fronts".