The Revenge of the Ridge: An Arid First Half of Feburary

 The last few weeks have been much drier than normal in the Northwest....and the reason is clear.  A very persistent ridge located along the West Coast or just offshore.

This image below shows the difference (over the past month) from normal of the heights of the 500 hPa pressure surface --you can think of this as the difference of the pressure at 18,000 ft from normal for the last 30 days.  The dark red indicates pressures were MUCH higher than normal off our coast.  In weather vernacular, there was a major ridge offshore.

On the eastern side of ridges there is generally sinking air and dry conditions.  That is where we have been.


The last week?  Essentially the same pattern (see below).    One thing you will immediately notice is the wave-like nature of the atmosphere.  There is a ridge of high pressure offshore, but a trough over the central US, and a ridge over the West Coast.    This is called an amplified wave pattern.



What about the future?   Let's look at the best of the best!  The European Center ensemble predictions (many forecasts averaged).  All the images are from weatherbell.com, a really wonderful service that you can subscribe to.  They show the upper atmosphere heights (solid lines) and difference from normal (red to pink are much about normal)

A weak trough moves through on Monday, but by Tuesday evening a big ridge develops offshore.  And yes, a strong trough over the Midwest.


By Friday at 4 PM the ridge weakens a bit and moves towards our coast.

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And believe it or not, by next Tuesday (15 February) the ridge strengthens again and shifts a bit offshore.  The Ides of February.  And the Ides will be dry.


What about the predicted precipitation?  Here is the predicted difference from normal for the next ten days, where the reddish colors indicate below normal.

Yes...you guessed it....much drier than normal conditions are expected.  Sorry skiers.  But there should be more sun than usual.  Good for sufferers of SAD.

 The last few weeks have been much drier than normal in the Northwest The Revenge of the Ridge: An Arid First Half of Feburary

But it would be cruel of me to leave all of you forlorn of hope.  A number of long-range forecasts have suggested the potential for a regime change, with a cold, trough developing over the Northwest.   Here is the predicted upper-level flow on Sunday February 20th.   Blue indicates lower than normal pressure/heights.

A major trough over the West Coast!!

Skiers--you would like what this would do.   But the uncertainty that far out is great, so don't get too excited yet.



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