May 11, 2016

Major Cooling Ahead

We have all gotten used to the warm, sunny weather, which followed the warmest April on record for many Northwest cities.

But it is all going to end this weekend, with cool, showery weather settling in for an extended period.  

Real meteorologists prefer to look at the output of ensemble forecast systems that present the results of many predictions.  Here is the graphic from the North American Ensemble Forecasting System.   Warming through Friday...and then bang... an extended cool off, with increased chances of precipitation and clouds (the yellow boxes show the range of the middle 50% of the ensembles, the "whiskers" indicating the range of the predictions.

The latest 6-10 day predictions of the National Weather Service Climate Prediction Center?  Cool and wet over the region.

The precipitation total for the 72h ending 5 PM on Tuesday?  Wet!

Why the change?   The high pressure area over the West Coast is going to ridge heaven.  For example, at 5 PM Saturday, an area of low pressure is over us, with the ridge pushed inland (at 500 hPa, about 18,000 ft).  Cool.

 But look at Wed. at 11 AM!  Wow.  A strong low off of our coast, with moist southwesterly flow invading the Northwest.

So if you want to enjoy a sun-bathed walk in the park, do it during the next few days.   Thinking about planting some grass or a plant in your garden.  Do it NOW!  You won't have to water much.


  1. I am actually happy that the balance is coming! This is "CURRENTLY" through May 13th, the hottest spring on Record according to our Chief Meteorologist, Mark Nelsen. If this were to persist, I would be quite alarmed at the prospects of another scorching summer. I feel this cooler pattern may persist into the summer months as well, as a cooler than normal summer, seems to be a reasonable adjustment to the all time record breaking heat we have been seeing. BTW, how is our dear old friend "The Blob"?

  2. Finally!

    Part of me will definitely miss the warmth (doubly so since I'll be doing lots of outside stuff in the coming days), but our trees need some coolness and moisture if they aren't to get super-stressed during the summer dry season. Not to mention wildfire risk later on.

  3. Hi Cliff, The Farm's Almanac predicted the cooler wet weather for next week. How do they develop their forecasts and how often are the correct? I have been watching the weather because we have a family event next week. So far the Almanac has been pretty accurate for the month of April and May.

  4. Thank you for another nice article, Cliff.

    It will be nice to have a week or so of *average* May temperatures. This is the second year in a row that my lawn looks like the date is August, rather than May. It will be nice to get a reprieve from the daily watering now necessary for my young plants in the vegetable garden.

    Average May and June temperatures I can handle. It is the weeks of BELOW average temps that wreak havoc on a vegetable garden. And, we have certainly had those in some years...

  5. Hi Cliff,

    I'd like a good lesson on normal variation - what's the base line, is standard deviation part of it? How many times can a number be 'above average, or how high above average before it is outside of normal variation? How many excursions does it take to alter what is considered normal variation? Does the length of the baseline impact the definition of normal variation? When/how/how often do we establish a 'new normal'?

    I think a good briefing for the layperson from a great teacher like yourself would help our ability to understand the conversation about "record breaking", "climate change" and "it's just normal."



  6. Finally, thank you low pressure and goodbye ridge. Don't return until mid July!!!

  7. Hmm, well Cliff's blog is certainly at odds with the NOAA forecast for Seattle through Tuesday, as of Thursday afternoon. The accumulated precipitation through Tuesday is less than 0.5". So we'll follow this to see what really happens.

  8. Cool and wet for a few days will help my property. Is it it just me or is the ground drier than usual for early May? Snowpack is melting extra fast.

    I felt a bit silly investing in drip irrigation this last winter for my hundreds of plants, fearing the El Nino. Especially after all the data saying the previous winter was so anomalous and this one turned out to be so wet. I was worrying about July and August, but I've been irrigating the last few weeks.

    Betting on the climate trending toward warm and dry in the short-term feels like a good choice again.

    So bring on the cool and wet. My tomatoes can wheel back into the greenhouse for a week or so.

  9. oh yes finally.. the weather that makes me happy and I can emerge from shade/air conditioning.

  10. "Cool, showery weather for an extended period"? I'll believe it when I see it - but there's little chance that'll happen. That prediction looks off even in Seattle & environs, more so up north here in north Whatcom County. We're currently looking at moderate temps and potential showers toward the end of next week. Nothing that will relieve the early onset need for irrigation.

  11. This is music to my ears! This year, quite literally, Seattle weather went immediately from a winter pattern to one of summer with no transition whatsoever.

    I was thrilled at first by the change, thinking it was merely a brief respite, but it turned out to be six weeks of barely any precipitation and temperatures more indicative of summer. I had thought we were hopelessly stuck in a massive ridge, were in for an even longer, hotter and drier summer than last, and that any rain more substantial than some very brief, very isolated showers would not come again until October.

    I really hope you are right about this! I love summer as much as the next person, but not three months early!

  12. so cliff, what do you think of the fires burning already? didn't you say that since it was so wet this winter, it wouldn't be a bad year? while others contend that snowpack is more important than precip...


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