Rain Shadow Effect in the
Pacific Northwest

Rain Shadow Effect. Here is how the Olympic Mountains in the Pacific Northwest produce a small semi-arid region in the heart of a temperate rain forest.

Washington's "Banana Belt"

Sequim, Port Townsend, and to a lesser extent Port Angeles, are located in what is referred to tongue-in-cheek as the banana belt of Washington State.

This is not because of the climate, which on average is cool-to-chilly, but because of the relative lack of rain.

While it’s raining buckets in Bremerton or Olympia, there may indeed be blue sky over Sequim caused by the Olympic Peninsula rain shadow. In fact, this condition is so frequently reliable, they call it the Blue Hole.

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Depending on the prevailing weather system, that blue hole may be over Sequim, Port Angeles, or Port Townsend; or it might be open enough to brighten all three towns, the southern parts of the San Juan Islands, and Victoria BC.

These fields near Sequim WA were irrigated prior to harvestThese fields in the Olympic rain shadow between Sequim and Port Angeles needed to be irrigated prior to harvest

Rain Shadow Effect in Sequim Washington

The blue hole is actually the result of a rainshadow effect caused by the Olympic Mountains directly to the south of Sequim Washington. The Olympic mountain range captures much of the incoming rain which falls heavily on the west and south slopes of the mountains.

As the air rises over the Olympic mountain peaks, the air quickly cools, triggering 100% relative humidity and then rainfall on the side of the mountains facing the prevailing winds. The weather that flows over the peaks to the lee side of the Olympics (facing north and east) has lost its moisture and is usually dry. See the graphic (Credit: Wikipedia)

The rain shadow robs the region to the north and east of the Olympic Mountain Range of rain. 

View a map of the Olympic rain shadow region here.

The Blue Hole

The following three photos were taken within minutes of each other on an early spring evening in Sequim-Dungeness.

Though the horizon was literally ringed with storm clouds, on this evening the Blue Hole over Sequim Washington prevailed.

Rainfall Averages in Sequim Washington
and the Nearby Pacific Northwest

Elk-adorned sign welcoming visitors to Sequim WA

Average yearly rainfall in...

These Pacific Northwest towns are not in the rainshadow:

  • Bellingham WA: 35 inches
  • Seattle WA: 38 inches
  • Olympia WA: 50 inches
  • Quilcene WA: 54 inches
  • Bremerton WA: 56 inches

Towns on the west and southwest slopes of the Olympic Mountains bear the brunt of the precipitation. Average yearly rainfall in...

We enjoy the rain shadow but when it does rain we don’t begrudge the sky.

Without the rain one would never know the beauty of the Pacific Northwest including its nearby temperate rain forests.

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