June 06, 2011

Onshore Push

Update 7 AM Tuesday...the push was fairly strong last night---and still quite breezy this morning. The satellite picture below shows low clouds pushing to the crest of the Cascades. Want sun today? Simply go over the passes. A few miles more and you will be in bright sun. But remember that places like Ellensberg will get hammered by strong NW winds today...and golf at Suncadia will be, lets say, a challenge. (and see the new video link at the end of this blog)

My wind chimes are ringing right now and the trees are starting to sway as the wind increases. Such behavior after a warm day means only one thing...an onshore push has started.

Temperatures rose into the low 70s over much of the western lowlands today, but as we enjoyed the warmth an upper level disturbance has been approaching and the difference in pressure between the coast and interior has been rising. These changes are producing an onshore surge of marine air that will bring a substantial cooling tomorrow (by at least 10F) and the return of low clouds in the morning.

Meteorologists follow the pressure differences very carefully during such events. North Bend, Oregon minus Sea-Tac is one that is popular. I prefer Hoquiam minus Seattle. As shown below, this pressure different grew from near zero to around 2.6 mb today....enough for a modest push. For a strong one you look for 3.5 to 4 mb. The times below are in GMT (18 is 10 AM, 00 is 5 PM)

Here is the predicted upper level chart for 2 AM this morning. You can see the trough--centered over Vancouver Island-- moving towards us. Onshore pushes with northwesterly flow tend to be be on the weak side.

Perhaps the best way to see a push in progress is by looking at the wind and temperatures from the Seattle Sand Point profiler (below). Time is on the x-axis and height (in meters) on the y axis. If you can read the blue wind vectors, you can see that the winds are now from the southwest in the lowest 1000 meters (roughly 3000 ft) and increasing....a good sign of an onshore push.

And the low clouds offshore have thickened and started to push in! (see satellite picture below)

So get your sweater out for tomorrow...highs will be in the lower 60s, clouds will dominate, and there even could be some light sprinkles. By the afternoon there could be some cloud breaks and maybe a bit of sun.

Onshore pushes are the main forecast problems during Northwest summers---some call it our version of air conditioning.

Finally, a key point is that we are in a very different pattern from the last few weeks--it may not be hot, but endless days of clouds and rain are NOT in the forecast.

KUOW: Several listeners delivered the petition with nearly 5000 signatories to KUOW today and talked with their program manager Jeff Hansen. KCPQ-TV (Channel 13) covered it....and should be on at 10 PM. Here is the segment on KCPQ:


KCPQ also gave me some time to talk about what I would have said on KUOW if I had been allowed. I am working on a detailed blog about my interactions with KUOW and particularly their reactions during the past few weeks. I really think KUOW has serious issues and I will try to analyze them in this work.


  1. re KUOW, I wonder if other guests were expected to stay 'on topic', and if so, what is the list of guests and what they were restricted to talk about. It should be open knowledge in the interest of editorial transparency

  2. Very nice Q13/Fox vid Professor Mass! short and gets the clear point across to the casual viewer.

    (unrelated to this...) as an amateur weather fan lacking instruments I write myself a lot of scripting language tools (python mostly) to follow the weather by making infrequent unburdensome (that's important, i feel) pulls of data off the web. So, for instance, where/which web-site could we get your Hoquiam and Seattle pressures? (NWS? NOAA? UW?) that is, i'd love to know from whence this data comes from. thankee!

  3. Where was the Protest March of the vast masses that support the KUOW position ? ;-)

  4. Cliff, I have a real weather question for you. What causes different types of rain?
    Yesterday morning as I was walking my dog along the water in Bellingham, the fine mist rain was like walking into a hose sprayer set on mist. I am used to getting wet in the morning, but rarely see this type of rain. What causes it?

  5. Cornbread...today there was lots of drizzle---small raindrops--- as you note. Such precipitation is from shallow clouds in which the drop sizes cannot grow large. ...cliff

  6. Do you have a longer term outlook for July/August/September? Will it be better than last year, or will it be full of the marine push? Visiting people would like to know!

  7. Hi Cliff, in watching your comments on KCPQ 13, I only have one thought in mind-for whatever it's worth. I think tying together the idea of why Math knowledge is so important to the Weather, practical applications in life, and other ideas you yourself can conjure. I believe this might be a way to show people how our kids have been left behind in the world. It helps the blue collar element watching the 10 o'clock news get concerned and want to do something. The Kahn Academy is a great resource for my kids, and wouldn't it be great if you did something similar, only more locally-since all of us care about the region and our success. Anyway, that's my two cent's, really miss hearing you on Friday's and am so pissed at Steve, and Katie.

  8. Thanks for the quick response Cliff.

    That was what I kind of suspected, but it seemed a little un-scientific to me. More proof things are indeed sometimes just what they seem.

    Thanks again.

  9. "...endless days of clouds and rain are NOT in the forecast."

    They may not have been in the forecast, but they sure have been in the sky.

    Why do Seattle forecasters consistently forecast for fewer clouds than actually occur? I would think the models would learn from this. Or the forecasters. Do you think a baseline forecast of 'overcast, light rain' every day would outperform the local forecasters.


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

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