Wednesday, February 23, 2011

PSCZ and Josh Ritter comments on Washington

Puget Sound Convergence Zone. Band of green shows rain/snow refection on radar
Image from Cliff Mass Weather Blog

I drove to Seattle yesterday through the convergent zone snow over north Seattle and then encountered a rather intense band of convergence zone snow on the way back home late last night north of Marysville. The Convergence Zone is a local northern Puget Sound weather phenomenon where air moving up from the south through the Puget lowlands encounters air wrapping around the Olympic Mountains from the north. The collision causes uplift and a band of rain, or if cold enough, snow. The CZ is a narrow band of cloudy weather and heavy precipitation well known to western Washington weather junkies. Anyone making the Interstate-5 drive between Bellingham and Seattle routinely knows that the band is narrow. So last night despite very bad visibility and very hard snow, I knew it would only last a few miles and 10 miles later we were out of the snow with starry skies. 

More of the same today with the added factor of Fraser outflow winds from the northeast bringing in a pulse of Arctic air. As the cold leading edge of the Fraser Arctic air pushes south into the moist air coming into the sound from the west and south, a band of heavy snow will fall. The sky to the south of Bellingham is dark and lots of snow in parts of Skagit County - a client of mine reported 6 inches, but only a few flakes so far in Bellingham with a breeze from the north.

The purpose of my Seattle trip was to see Josh Ritter at the Show Box. Josh grew up on the edge of the Washington landscape near Moscow, Idaho near the Washington border so he knows a few things about the Washington landscape. Apparently he had a bit of an adventure getting over Snoqualmie Pass yesterday as the pass was closed for a period of time due to heavy mountain snow.

Josh had a few funny lines about our landscape and what we value between songs:

He described driving to Washington State and crossing a subtle boundary between where taxidermy is prevalent to where it disappears and where coffee goes from terrible to OK to good.

He introduced another song by saying we would make Tacoma jealous.

His song Thin Blue Line mentions a place he calls Royal City and his band is called The Royal City Band derived from the reference in the song. I'm not sure Josh was singing about Washington States' Royal City, but he did mention it during the show.

A line from his song Harrisburg might fit yesterday's post on rail and coal "I believe the Garden of Eden was burned to make way for a train".

A song Josh Ritter did not play last night, but a favorite of mine might apply for those thinking of spring on this cold February day.


James said...

That convergence zone shown in the image actually formed alee of Vancouver Island rather than the Olympics. Often with such flow the Tacoma area gets the "normal" convergence event.

I also see that you called it the convergent zone with a "t." I take it that comes geology's "convergent boundary?" I've never liked using "zone" to describe what is typically a single solid band, but I'm not sure I can wage this semantic battle with you.

Dan McShane said...

James - Thanks for the catch on my use of the geologic term versus atmospheric.
As for a semantic battle on zone, it would not be with me - you'd have to take on the weather guys that coined the term.
Based on wind directions on Tuesday, I am fairly sure the band in the image is from the Olympics. It pushed southward later in the day and then northward at night. However, if you look closely at the image there is another band near Bellingham. This band is likley from the flow of air coming in the Strait of Juan de Fuca encountering the northwest flow coming down the Staits between Vancouver Island and the mainland.

The convergence zone does move around, and I do know it can show up in Tacoma (I lived there for the better part of year). However, it has been my experience that it is frequently north of Seattle in the winter.

James said...

Thanks for the reply, Dan. Google Reader "magically" recommended your blog to me and I continue to be grateful. Other natural science bloggers around the PNW could learn a thing of two from your style. Keep up the good work.