Epic Olympic Rain Shadow brings wild range of rainfall totals from Monday storm
Monday's storm provided Western Washington residents a virtual menu choice of how much rain you wanted. If you wanted 7-8 inches of rain? There's a spot that got that much. Want hardly any rain? We had that too -- and pretty much any number you wanted in between.
But perhaps nowhere was the choice so stark than along the Olympic Peninsula where there the difference between several inches of rain and hardly any rain was just a few miles apart.
During the 48-hour period between 7 a.m. Sunday through 7 a.m. Tuesday, a rain gauge 2 miles northwest of Sequim reported just a paltry 0.17" of rain. But another gauge just a few miles away closer to the Olympic Mountain foothills (but listed as just 2 miles southwest of Sequim) reported 3.55 inches of rain over the same period!
It's all thanks to the Olympic Rain Shadow -- a staple in making for variable weather during Pacific storms.
The Olympic Mountains act as a wall that protects the northeastern Olympic Peninsula and San Juan Islands from the bulk of the rain that moves into the Pacific Northwest. The dominant during Monday's storm was from the southwest. As that air runs into the southwestern face of the Olympics, the mountains push the air upward. As the air lifts, it condenses and squeezes out its moisture -- think of it as the mountains acting like a sponge soaking up and then squeezing out the rain.
Check out some of the rainfall totals on that side of the mountains: Owl Mountain reported 8.25 inches, while Humptulips had 7.42 inches, Elk Meadows had 7.23 inches and Forks had 5.23 inches.
But on the other side of the mountains, it's the total opposite. Once the air reaches the Olympic Summit, now it's pretty much lost its moisture. As it goes over the top of the mountains and comes down the northeastern slopes, it sinks. And just like rising air condenses, sinking air dries out as it encounters warmer air near the surface. So you already have semi-dry air becoming even drier.
That left much of the area northeast of the Olympics without much of any rain. Coupeville had just 0.12 inches, while Port Townsend had 0.09" and Gardiner, just east of Sequim, only had 0.05 inches!
You can see this graphically via the National Weather Service: Look at the big dry spot!
And you can see the large gradient of rainfall totals over such a short distance around Sequim:
That area only averages about 17" of rain a year, but rainfall totals increase about 1" per year for every mile you drive west! Forks, about 90 miles west, gets 120" of rain a year!
The rain shadow extends into the North Puget Sound region, and then it's a sliding scale of more rain as you get farther south. Seattle received 1.72" at Sea-Tac Airport between 4 a.m. Monday and Tuesday, which was more rain in 24 hours than the city received in the 3300+ hours between May 1 and Sept. 15 this year (1.66 inches.)
But if a rainy day is getting you down, just head up to Sequim, where it's probaly not raining (or at least, not as much). Just... don't go too far beyond the town!