Just as location is the key in real estate, so is location the key in understanding the sometimes maddening variety of weather in the Puget...
Blame it on the mountains, the water, the wind, but all that wacky weather in South Snohomish County can be attributed to something called the Puget Sound Convergence Zone.
Just as location is the key in real estate, so is location the key in understanding the sometimes maddening variety of weather in the Puget Sound area.
The complex combination of hills, mountains and water produces great differences in weather over very short distances. South Snohomish County is home to one such pattern.
The Puget Sound Convergence Zone may be the focus of heavy precipitation while other areas just a few miles to the north or south are enjoying brilliant sunshine.
Most Read Local Stories
- In Seattle's Sodo district, frustration mounts amid RVs, drugs and skyrocketing crime VIEW
- Outrageous! Seattle isn't the best coffee city in the country, says new survey
- Seattle woman faces eviction for failing to pay $2 she owed in rent
- Seattle is home to two women's marches this weekend amid divisions within local, national orgs
- Sammamish man killed parents, self because he didn't want mother to sell family home, sheriff's office says
This zone often develops after a cold front moves through; high pressure building near or just offshore produces winds along the coast from the west-southwest to northwest.
When this onshore flow of air runs into the Olympic Mountains, it splits, some flowing through the Strait of Juan de Fuca to the north, some around the south end of the Olympics through what’s called the Chehalis gap.
To the east, the Cascade Mountain range presents an almost insurmountable barrier. That deflects some of the eastward moving air into Puget Sound; the air that’s moved through the Strait of Juan de Fuca moves through Admiralty Inlet into the north end of the Sound, while some of the air moving around the south end of the Olympics heads northward.
A map makes this easier to visualize. The most common place for these two opposing currents to collide or converge is over north King and south Snohomish counties.
The rising air within this convergence zone may only produce thicker clouds, but a stronger zone can produce locally heavy rain or snowfall, and possibly even thundershowers.
Although this zone can shift position over time, it usually doesn’t move very quickly, which leads to locally heavy rain or snowfall.
One snowstorm that developed within the convergence zone produced up to 20 inches of snow, while areas just to the south and north picked up only trace amounts.
Although it can make getting around miserable, such convergence zones can produce wonderful snow at Stevens Pass — a treasure for skiers and snowboarders during the winter months.