The weather in the Pacific Northwest is influenced by both the large bodies of water and the complex topography of the region. The Pacific Ocean, the Olympic Mountains, Puget Sound, and the Cascade Mountain range all impact local weather conditions. These contributing factors lead to weather conditions that vary significantly from one location to the next; for example, it may be storming in Everett while it is clear and sunny in Tacoma.
Because these influences are unique in the continental United States, newcomers are often confused by the weather terminology common to Western Washington. Here is a glossary of terms often heard on local weather reports:
Air mass
A large expanse of air having similar temperature and humidity at any given height.
Beaufort scale
A scale of wind strength based on visual assessment of the effects of wind on seas and vegetation.
Chinook
A warm, dry wind on the eastern side of mountains, often resulting in a quick winter thaw.
Cloud base
The lowest portion of a cloud.
Cloud deck
The top of a cloud layer, usually viewed from an aircraft.
Condensation nuclei
Small particles in the atmosphere that serve as the core of tiny condensing cloud droplets. These may be dust, salt, or other material.
Convergence Zone
An atmospheric condition that exists when the winds cause a horizontal net inflow of air into a specified region. In the case of Western Washington, winds in the upper atmosphere are split by the Olympic Mountains, then re-converge over the Puget Sound region. The resulting updrafts can create convection currents, leading to rain showers or stormy conditions.
Cutoff high
Anticyclonic circulation system that separates from the prevailing westerly airflow and therefore remains stationary.
Cutoff low
Cyclonic circulation system that separates from the prevailing westerly airflow and therefore remains stationary.
Deposition nuclei
Tiny particles in the atmosphere that serve as the core of tiny ice crystals as water vapor changes to the solid form. These are also called ice nuclei.
Diffraction
The bending of light around objects, such as cloud and fog droplets, producing fringes of light and dark or colored bands.
Drizzle
Small drops between 0.2 and 0.5 mm in diameter that fall slowly and reduce visibility more than light rain.
Eddy
A small volume of air (or any fluid) that behaves differently from the larger flow in which it exists.
Halos
Rings or arcs that encircle the sun or moon when seen through an ice crystal cloud or a sky filled with falling ice crystals. Halos are produced by refraction of light.
