Heavy rain, big snow, high winds, weird clouds — how Mount Rainier affects the weather | KNKX

Heavy rain, big snow, high winds, weird clouds — how Mount Rainier affects the weather

Mar 13, 2020

Mount Rainier looms on horizons in the region like no other, dominating views when visible – or “out” as locals like to say. This massive 14,000-foot peak is an active volcano that inspires awe in visitors to the region and stands as one of our most recognizable icons.

It also has a profound effect on the weather around it – because of its size.

“Mount Rainier is a huge barrier to the flow coming in off the Pacific Ocean,” says KNKX weather expert Cliff Mass, who is a professor of atmospheric sciences at the University of Washington.

“The first thing it does is cause a major increase of precipitation, as the air goes up the windward or the southwest side of the mountain,” Mass says.

The air accelerates. That leads to heavy precipitation in places such as Paradise, which gets an astounding 112 inches of rain per year.

As it goes over the mountain and down the other side, the air dries, compresses and sinks, creating a major rain shadow, with much drier conditions on the northeast, lee side.

Mass says even Sunrise, located pretty high on that side, at about 6,000 feet, gets only about 75 inches per year.

The profound rain shadow effect is just the beginning of the weather phenomena on Rainier. Other impressive features include:

  • Major snowfall: Paradise got 1,122 inches of snow in 1971-72 (or about 93-and-a-half feet), setting an all-time world record for annual snowfall. It was the most snow seen that year “anyplace – and I mean anyplace in the world,” Mass says.
  • Wind: Winds increase greatly as air from the ocean hits the mountain, accelerating as they move upward. This affects some places profoundly, such as Camp Muir at about 10,000 feet. “It is not unusual for them to get winds gusting above 150 mph,” Mass says.
  • Peculiar clouds: They form as the air approaches the mountain and are almost all lens-shaped, or “lenticular” because of the way they are created. They include cap clouds, that can look like a hat perched near the top of the mountain, and wave clouds that can stack up like plates. They also often move swiftly through the atmosphere, resembling flying saucers. This caused a notorious “UFO craze” in 1948, when a private pilot named Kenneth Arnold famously mistook them for space craft from a different world.

“We can be proud,” Mass says of our state’s distinction in starting that craze. “But we know today that this was basically a mountain wave cloud, produced by Mount Rainier.”

Weather with Cliff Mass airs at 9:02 a.m. Friday, right after BirdNote, and twice on Friday afternoons during All Things Considered. The feature is hosted by KNKX environment reporter Bellamy Pailthorp. Cliff Mass is a University of Washington professor of atmospheric sciences, a renowned Seattle weather prognosticator, and a popular weather blogger. You can also subscribe to podcasts of Weather with Cliff Mass shows, via iTunes or Google Play.