July 30, 2010

Weather Changes this Weekend and Boater Alert

9AM view in Seattle looking toward Mt. Rainer

noon--brightening up

3PM: cool, cloudy air all mixed out and some convection over the mountains.

Today was an interesting day, really dense fog and low clouds over much of the west, with some drizzle in some locations (like on me as I biked in today). (see images above)

Believe it or not, when you see such low visibility it is generally a good sign--an indication of a very shallow saturated layer. Anyway, the murk rapidly evaporated away during the late morning and temperatures rose very rapidly as the thin cool layer mixed out and was replaced by warmer air aloft.

Now this weekend will have its issues, not the least is a considerable potential for rain and thunderstorms on Saturday. The initiator: a sharp upper level trough that will move through during the day (see graphic) and which will cause enough upward motion to get some instability going. By the way, those in western Washington could have looked eastward and seen some instability clouds (cumulus) over the Cascades later in the afternoon today.

Look at the forecast precipitation maps for tomorrow--take your umbrella if you head into eastern Washington and keep a look out if you are planning a hike in the high country. A particular threat in the N. Cascades.

Onshore flow is increasing tonight and with that pesky trough in the neighborhood, tomorrow will be a big step down for western WA. Low clouds will reform tonight and they will not give way easily tomorrow...particularly in the central and southern Sound. Yes, perhaps cloudy all day.

So what do you do? Stay in the murk in the west? Head to eastern WA and get wet? My recommendation--head for the western slopes of the Cascades. Should be dry, high enough to get out of the low clouds. A good choice...something like Tiger Mountain where you could hike above the low clouds...always fun.

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  1. Just a comment on the western Washington murk. I live in Bellingham just east of downtown and we have been fog free all week. It got within a few blocks but something about our local air flow generally keeps us in the clear.
    Very much enjoy your blog.

  2. Good call on the rain Cliff!

    Bellingham has had a pretty fair amount today (for July) and it wasn't even mentioned on the NWS site at all.

  3. Very stormy over here in Eburg today!

  4. 4pm Saturday, Supercellular type storm moving down the i82 corridor. 1 inch hail moving down the heart of fruit and vineyard country. Just aweful

  5. I have a question as a fellow bike commuter: Is my perception that we've had winds from the south-ish in the mornings and north-ish in the afternoons lately accurate? Every morning I ride south and it feels like I'm riding into the wind; then when I ride home in the afternoon, same thing!

    I'm just hoping this isn't the usual biking breeze that I'm feeling, or else I'm gonna have to build up some more endurance and stop complaining about the "headwind both ways."

  6. I've long contemplated the headwind both ways phenomenon riding south, then north. Since mornings are more likely calm, the only wind is going to be a south wind in stormy weather. Afternoons are more likely to have a fair weather north wind. Given these two factors, you have a slightly elevated probability of a headwind both ways.

  7. Regarding the headwinds both ways issue--here is the explanation in budget sound.

    During the morning the winds are often nearly calm, or during days like last week, southerly. Head south (like I do), you have a headwind. During the day the clouds break and the ground warms. A large scale sea breeze forms here..the sound breeze...which is from the north. So going home you have a headwind!

    During the winter there are southerlies the whole day...cliff

  8. When are we going to get some rain here in the north sound? Things are getting really bad -- no meaningful rain for over a month. Are we approaching the record for consecutive days with no measurable precip in the north sound, say Friday Harbor or Bellingham?


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