May 13, 2016

Arid Spring

I have been doing a lot of gardening the past week, and I am startled by how dry the soil is.

What is particularly surprising is the aridity of the soil following the wettest winter in Northwest history.  The lack of rain was accompanied by very warm temperatures (April was the warmest on record at several western WA location, which has led to an earlier start of the fire season, with several wildfires west of the Cascades.  The picture below shows a fire in Snohomish County.

So what happened?  Let's start by looking at the percentage of normal precipitation for the past two weeks (below). Western WA and Oregon are very dry, with some locations at less than 5% of normal.

But percentages can be deceiving--here is the departure of observed precipitation from normal for the same period.  Less scary....but you will notice that some areas of western Washington are down a bit over two inches.  Much better situation east of the Cascades and over California/Nevada.

What about the entire spring?  Here are similar figures for the last 60 days.   For the percent of normal precipitation, much of the Northwest is well below normal--some locations 25-50% of normal.

Departure of accumulated precipitation?  2-6 inches in western Washington, 0-2 inches in eastern WA.  

So why have we been so dry and warm here in western Washington?   The key cause is persistent high pressure (ridging ) aloft.    Here is the difference from normal (anomaly) over the past 30 days for upper level  (500 hPa) heights (like pressure).  Above normal heights (yellow colors) over SW Canada and the northern portions of the Northwest).    Such ridging brings sinking air and dry/warm conditions.

This persistent pattern is rapidly evolving and next week an area of low pressure will move towards our coast.  The result will be clouds and rain.     Take a look at the latest 6-10 day precipitation forecast by the Climate Prediction Center.  Above normal precipitation over our region.  I suspect this will end the fire threat for a while.

KPLU Event!

Meet an astronaut (and me) tomorrow (Saturday, May 14) at the Museum of Flight for a KPLU fundraiser (music at 6 PM) and presentation (7PM).  Information here:


  1. More bizarre than the dryness is the extreme heat. The snotel sites is startling.... The haze from area fires (mostly prescribed) was very evident today. Driving through the gorge today there was something raging on the Oregon side enshrouding Mt. Hood. Welcome to the new normal of extreme wildfire behavior in the PNW.


    Would evapotranspiration not be the correct explanation for the dry ground? I am baffled by the fact that no meteorologist or climatologist talks about evapotranspiration(ET). Nor have I found any studies of the impact of climate change on ET (hint, hint). A warming planet means ET could be significantly increased.

    For those of you not familiar with this term, evapotranspiration describes the part of the water cycle which removes liquid water from an area with vegetation and into the atmosphere by the processes of both transpiration (plants breathing out) and evaporation. It “consumes” more water than humans i.e. reservoirs lose more water to ET than to human consumption.

    Here in Canada we have an excellent ET website
    Selecting the University of Victoria location (where I live) on the station map
    shows a YTD moisture deficit (precip minus ET) of 136mm.

    With climate change this is (IMHO) an extremely important issue to consider so the lack of it being mentioned is really baffling to me. As a hobbyist your professional comment on this subject would be appreciated.

  3. Cliff - at what point do you come to the conclusion that the high-pressure ridging is the new 'normal' for Pacific Northwest? This is not abnormal anymore for us...

  4. Rick...plenty of meteorologists talk about Evapotranspiration. In fact, that is why I talked about both precipitation and temperature. We have dry soil due to both lack of precipitation and warm temperatures. There are MANY studies of ET and climate change. ..cliff

  5. Thanks for the rain today, Cliff.

    My back needs a rest because I water my garden with watering cans. That practice puts the water only where it is needed. As they say: pay me now, or pay me later. I prefer to not use sprinklers because then I have weeds to pull everywhere.

    Needless to say, this spring has been dry and very warm. My 64 year old back thanks you, Cliff!



  6. nice article on deceptive KUOW in the Seattle Times today.

    KUOW definitely needs NO MORE pledge money to stuff slush funds for a long time.

    Thanks, Cliff, for doing a big part in saving KPLU!


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

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