March 10, 2021
Forecast: March 10th, 2021 (Evening Update)
By Chris Thomas
Sunny with a high around 50 degrees – spring weather doesn’t get much better than this!
Just step outside for a moment and you’ll likely see folks out walking their dogs (without rain jackets!), daffodils starting to bloom, people sitting out on their patios, and sunshine abound. Sunny days like this are just one of the things that make Western Washington such a wonderful place to live!
We definitely have our share of clouds and rain here though, so unless you are one of that rare breed that actually enjoys that type of weather like I do, winters here leave many folks longing for warm and tropical places to escape to such as Hawaii. Though the climate in Western Washington is quite different from that of Hawaii, the two share one big thing in common: the effects of rain shadows.
What’s a rain shadow? As winds blow moist air toward mountainous terrain, the air rises, condenses and causes precipitation. By the time the air reaches the top of the terrain, little moisture is left and the air continues to dry out as it sinks back down the slopes on the other side. This creates a situation where locations on one side of mountainous terrain can receive precipitation while locations on the opposite side may see dry weather and even some sunshine. These dry areas are said to be in a rain shadow.
Image credit: https://www.britannica.com/science/orographic-precipitation
In Western Washington, winds associated with weather systems are often out of the southwest, which means that areas to the southwest of the Olympics often see wet weather while locations to the northeast such as Sequim see drier weather and receive far less precipitation annually. Similarly, Hawaii’s mountainous terrain means that parts of the island chain are also impacted by rain shadowing.
In fact, a major rain event brought over 15” of rain to parts of northeastern Oahu on Monday and Tuesday. Meanwhile, the direction of the winds relative to the mountains created a shadowing effect and brought considerably less precipitation to southwest portions of the island. While the Kahuku Training Area on northern Oahu received 5.53″ of rain in a 24 hour period, rain shadowed locations on the south and west side of the island received drastically less. Ewa Beach for example only received .07″ of rain. That’s quite a difference, especially compared to the 16.01″ recorded near Ewa Forest Reserve!
24 Hour Oahu Rainfall from 10:45 AM HST March 10, 2021 / Image credit: weather.gov/hfo/rain_summary
The heavy rainfall in certain parts of the island even lead to the need for some evacuation orders and prompted the Honolulu National Weather Service to declare a Flash Flood Emergency yesterday. Similar heavy rain and flooding impacted the other Hawaiian islands as well, including Kauai, where several landslides were reported.
This dramatic example of rain shadowing illustrates that while in most regards Hawaii and Western Washington weather couldn’t be more different, they do have this one very impactful thing in common. So, the next time it is cloudy and damp here and you find yourself daydreaming of warm and tropical Hawaii, remember that the two places may just have more in common than you think. Until then, enjoy today’s sunny weather!
Reach forecaster Chris Thomas at theuwdawgcast@uw.edu. Twitter: @chrisevanthomas.
