June 14, 2011

Puget Sound Convergence Zone

Late spring is the convergence zone time of the year and we have one tonight. Take a look at the latest radar image and you can see the band of precipitation north of Seattle (see graphic). This one is somewhat amorphous--partially because the atmosphere is not that unstable (this gives you a nice line of convection).

Now let me show you something that you won't see on TV tonight..the Doppler velocities for the same time. We don't call it a Doppler radar for nothing! But you never see that on TV.

Funny side story. KING-5 got their own Doppler radar years ago, and my colleague Jeff Renner, excited about it like a little kid on Christmas morn, showed both the reflectivity (precipitation intensity map) AND the Doppler velocities. This did not last long. These Doppler velocity maps are a bit difficult to read. They show you the component of the velocity of the target (here rain) towards or away from the radar--NOT the total wind speed. It takes some experience to really figure out what is going on...and the colors can be confusing. Anyway, here it is:

Makes perfect sense, right? Warm colors indicate flow moving away from the radar, Grey, no velocity towards or away, and cold colors, flow towards the radar. And remember the radar is on Camano Island. So looking a this radar one concludes that there are northerlies over the north sound, and a line of zero velocity--the convergence zone--stretching east-west over Seattle. In general, convergence zone precipitation is north of the low-level convergence line. Well, here are the winds at 9 AM (click to make big). Northwest winds on the coast and a nice convergence zone in the surface wind field. Classic.

Why do Puget Sound convergence zones prefer spring? Because the winds on the coast are more frequently from the west to northwest during this time of the year. In mid-winter, when the flow is more southwesterly, the convergence tend to be weaker and farther northwestward. And the air is generally more unstable during the spring as the surface warms more rapidly than the air aloft.

After the convergence zone passes south of you (with a switch from southerlies to northerlies at the surface), southerlies are usually still aloft. If you look carefully you can see it in the cloud motions. Here is a video for today...see if you can see the differing wind directions right before sunset:

Anyway, if you like Doppler velocities they are always available on the National Weather Service and UW websites, among others.

For those that are in the high tech industry and are located downtown, I will be giving a talk at a Blink open house on high-tech weather prediction on Thursday at 5:30 PM in Seattle. For more info and to RSVP, see: http://blinkux.com/insights/blog/blink-open-house-speaker-series/

And those of you interested in provide feedback to KUOW don't forget, this facebook site dedicated to listener comments:

KUOW Listeners Speak Out

I am now talking to a variety of local radio stations and will be finding a new home during the next few weeks.


  1. I did notice the sunset wind shift... points to me. :-)

    I'm so glad you're in the process of finding another radio home. The blog and podcast are great but they (by definition) do not reach the uninitiated public.

    Once you find a permanent radio home, I'd love to see you continue with a periodic education-opinions podcast and (pretty-please-with-a-cherry-on-top!) would be thrilled if you would occasionally do a high-level, explain complicated weather things geek-out podcast. I know that such a challenging podcast might be beyond my knowledge or even my math abilities, but I sure would enjoy the push and would study it and the necessary topics until I understood it. The chances of me getting to audit or actually take your courses are next to none, but this stuff fascinates me.

    Anyway, enough shameless begging LOL I am planting my tomatoes and pepper plants THIS WEEKEND. I can't stand waiting another minute longer, but all the people in my community garden who have already planted their tomatoes have early blight... it's going to be hard to keep my plants healthy.

  2. "and the colors can be confusing..."

    Yes, that is one of the most horribly chosen color scales I've ever seen. And it perplexes me why weather people put up with things like that. You all have computers, why not use them and change the colors?

  3. I hope you can be on more than one station. Our new local Community Radio Station is KPTZ in Port Townsend.


  4. When I was living in Michigan, the TV stations would occasionally pull up the Doppler map if there was a particularly good example of a hook echo. (Lots of tornadic storms in MI.)

    Live weather radar really changed how TV stations did tornado alerts. Before they had access to it, they mostly just repeated the NWS warnings in a crawl and left it at that. Being able to show on-screen, live, where the storms were and where they were going really made it all a lot more clear.

  5. Even Juan Williams found a better place at a more tolerable station, and so will you. Best of Luck Cliff!

  6. Prof. Mass,

    Is it totally out of the question that you could continue on KUOW? To me, the nexus between your expertise as a UW professor and the public radio station based at the UW is obvious. Is there no possible way that some common ground could be found?

    I recently renounced my long-standing membership with KUOW because of your firing. I sent an e-mail detailing my reasons to a number of people at KUOW. I was surprised to receive some detailed responses. The fact that they even responded indicated to me that the issue is still alive for them.

    I really think you should be on KUOW. I know you have issues with them but no situation is ever perfect.

    Just a thought but if an independent mediator were brought into the picture would you be willing to participate?

    You are a true resource to the community at large and to me it would be tragic if so path couldn't be found where a UW professor devoted to communicating his field to his community couldn't have a place on our community's public radio station.

  7. Jim,
    It is not out of the question on my side, but they appear to be completely uninterested. I have tried contacting them, but they won't engage in any conversation in finding some kind of compromise. This attitude says a great deal about the management there. There way or the highway, to use a common expression...cliff


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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