October 12, 2013

Big Ridge and Extraordinary Fall Weather Ahead

We had a marvelous summer.  Then during the second half of September we were tested by some unseasonably wet and windy weather.  And last week has been nothing to brag about.

But everything is about to change. The next week is going to be glorious, with no precipitation, warming temperatures, and plenty of sun.  Some clouds midweek and maybe some morning fog on a few days...but nothing serious.

Who or what should you thank for this boon?   A high amplitude, persistent ridge of high pressure in the eastern Pacific that will be locked down for many days.  What meteorologists call a blocking pattern.

Let me show you some graphics:  a series of upper-level maps (500 hPa heights--the height of the 500 hPa pressure above sea level).  As you know, high heights are associated with descending air and dry/warm conditions.  The best conditions in the midlatitudes are just downstream (in this case east) of the center of the ridge.

This morning we find a weak trough over the Northwest...and yes plenty of clouds and some showers are being observed.  There are rapidly weakening now and I am hopeful for dry conditions by the time of the big game.  Ducks don't like dry weather.

 But by Sunday morning at 5 AM, the trough is past and has strengthened over the Southwest (image below).  Big ridge over the eastern Pacific.

Folks this is a very favorable pattern for us...if you like sun and warmth that is.  You notice there are strong troughs (areas of low heights or pressures) on both sides of the ridge?   We are seeing the development of an omega block...looks like the Greek letter omega... which is often a very stable and persistent pattern.

 Monday...the ridge is still there!
 On Tuesday, a modest trough is approaching our region....expect increasingly clouds during the day.
 But Wednesday afternoon, the big ridge is back and bigger than ever.  Wow.

 Now, what I have shown you above is from the UW model runs driven by the American GFS global model.   What about the gold-standard European Center model?  Here are upper level (500 hPa) heights and lower atmosphere temperatures (shaded, around 5000 ft) for Thursday afternoon from the EC model.  Big ridge still there.

 Sunday afternoon?  Still there.
I have examined the forecasts of other modeling systems, including the European Center and U.S. ensembles.   Lots of consistency, which provides substantial confidence in good weather ahead for the Northwest.   Expect 60s this week.   The only thing to worry about when we get ridges over us in the fall is fog, particularly during the morning.  This is particularly a threat Sunday and Monday AM.   But by later in the week the air will dry and there should be more offshore flow, so little fog would be expected. 

And to show you that the National Weather Service is on board with this forecast, here is the 6-10 day forecast from the Climate Prediction Center.  Warmer than normal over us.  WAY warmer than normal over Alaska.  Good time for a cruise.

Finally, let me remind those in Bellingham that I will be talking about the future of weather forecasting at Bellingham High School on Tuesday night at 7 PM.  More information here.


  1. Awesome news! The old curmudgeon in me predicted that because we had a rare pleasant June, our typical burst of good weather in Sept./Oct. would be missing. Not entirely!

  2. I seem to recall a lot of Models predicting a nice September too. I'll just wait and see, but thanks.

  3. "Ducks don't like dry weather."

    I'm afraid these speedy Ducks do, though I don't think it would have mattered either way.

  4. Plenty of sun, my foot. #forecastfail

  5. ".. Wednesday afternoon, the big ridge is back and bigger than ever." .. What changed, that the models had apparently not accounted for, having lead to this idea not having come about, would you say professor Mass. ?

  6. Cliff, you are personally responsible for the fact that my brother in north coastal San Diego County has a severe case of WeatherGeek Envy.
    Keep up the excellent blog.


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