October Begins Cool, & Water Year Ends

6:30pm Sunday…

It’s been a real quiet weather weekend with just a few sprinkles/showers yesterday and today. Officially we’ve had all of…wait for it…  .01″ in Portland.  That’s weekend total.  I know a few of you had more, but overall boring for weather geeks like me.

Tonight (the end of September) wraps up the “Water Year”.  If you’re new to the Pacific Northwest there’s a very good chance you’ve never heard such a phrase.  Here’s the deal…our rainy season is late October through March; during the cool season.  As you know, we have a very dry warm season here compared to areas east of the Rockies.  That’s May through September.  All that winter rain (in the ground) and snowmelt (coming down rivers) is used to sustain our lives/properties/crops through the dry season.  So it’s important to know how wet our rainy season is each year.  But each rainy season crosses from the end of one calendar year into the first part of the next calendar year.  So for the purposes of ranking our wet seasons, we use a “water year”.  That year begins on October 1st and ends September 30th.  Make sense?

How did we do this year?  We ended up drier than average by 6″or so.  Here’s a nifty little chart from the folks over at Portland NWS.  Winter rainfall was just about normal until we hit February.  But that month and March were drier.  Then a very wet first half of April brought us back to close to average again.  And you know the rest of the story…we’ve pretty much flat-lined since that time.


Comparing this water year to recent years shows we had two very wet “wet seasons” and now we’ve experienced a dry one.  You can see the big year to year variability.

Rain WaterYearPDX

The water year gauge “resets” at midnight and we begin a brand new year.

Here’s what I see for this first week of October:

  1. Next few days feature a splitty flow with a southern system moving into California giving them a much needed rain.  We get a weak system dragging through here tomorrow night and Tuesday morning; sprinkles/showers at most during that time
  2. A large upper-level ridge wants to develop out in the Gulf of Alaska (just to our west) later this week and through early next week.  This means a real lack of storminess in the eastern Pacific but also quite chilly air (for early October) just to our east.  Notice all 3 big models (GEM/ECMWF/GFS) show the same pattern for NEXT Monday, the 8th…one week from tomorrow

This slideshow requires JavaScript.

A slight move westward and we’re into an unusually chilly (early frost?) pattern all across the Pacific Northwest.  A slight move east or a weaker ridge (ECMWF) would mean cloudier, but mild and occasionally wet weather.   We’ll see how it works out and how much rain we get next weekend.  ECMWF was somewhat wet so I went with that model.

3. No sign of a stormy October weather pattern.  With a large ridge out there we’re sure not going to see an extra-early start to the Pacific storm season here on the West Coast.

4.  Cool temps, or at least cooler than average.  We’re done with 80 degree temps and at this rate there’s no reason we couldn’t be done with 75 too.  Check out those ECMWF ensemble forecast highs the next two weeks…pretty cool this weekend and early next week


So the next week will be cooler than average with more showers toward the weekend but not a “start of the wet season”.

Chief Meteorologist Mark Nelsen

32 Responses to October Begins Cool, & Water Year Ends

  1. Sergey says:

    Hey guys, where can I find historical precipitation data for a certain city like Astoria, I want to find daily precip totals for specific days from like a month ago. I tried checking the NWS site, but it’s so hard to navigate… any suggestions?

    • ron says:

      Not sure about historical data, but a nice current conditions site for the North Coast with webcams can be found by doing a Google search for “Brevins weather.”

  2. Ken in Wood Village says:

    I think I just throw-up a little in my mouth…LMAO

  3. Ken in Wood Village says:

    The 00Z Euro is looking good 🙂

  4. 40˚F overnight, coldest night of the season so far. Just lit the pilot and turned the heat on for the first time this season.

    • Roland Derksen says:

      36.7F for a low here this morning. That’s my coolest minimum for this date, beating 37.9F back in 2013.

  5. Ken in Wood Village says:

    Hmmm, anyone look at the 00Z GFS? It looks cool and very wet.

    • Mike says:

      Does anyone know where you can download an entire season of animated water vapor action? I would love to be able to watch how the seasons change and how a stubborn high pressure system finally gets knocked out. Thank you

  6. Sergey says:

    Hey guys where could I find historical rainfall for Astoria, OR?
    Something like the Hydra network for Portland but for Astoria.

  7. Sergey says:

    Hey guys where could I find historical rainfall for Astoria, OR?
    Something like the Hydra network for Portland but for Astoria.

  8. Ken in Wood Village says:

    I’m surprised you all haven’t been talking about the models? I swear I can hear crickets in this blog!!

    • Joshua Lake Oswego says:

      I am looking forward to the first widespread rain in Moses knows how long. Some nice crisp nights and cool fall days are appreciated too. Friday will be heavenly.

      • Ken in Wood Village says:

        Hey Joshua…been awhile. I went to see a movie tonight with my sister and her husband (and my little niece). I’m wearing shorts because it was nice out but when we got out of the movie, it was a little crisp…lol. I love it. Friday will be the first taste of fall 🙂

        • Joshua Lake Oswego says:

          Yes, sir. Already cooler than this morning’s very warm low. Enjoy the upcoming weather. It might just stick around for a while.

    • K says:

      Oh, no, I’m excited. First storm of the season Friday, even though it is quite weak.

      • Ken in Wood Village says:

        Hehe, I know how you feel. Even though it’s a weak one, it’s a start. I’m hoping we will start seeing more storms come our way and hope they start getting stronger 🙂

    • Big windstorm on this day (and evening) 51 years ago. Season is starting

  9. Ken in Wood Village says:

    Wow, The 00Z Euro sure got wetter later in the run but it’s just wish casting 🙂

  10. Ken in Wood Village says:

    I’m starting to like the models more and more 🙂

  11. Nice setup, now let’s get some retrogression so we can all have an early freeze!

  12. Roland Derksen says:

    The Water year here ended on a watery note yesterday (0.90 inches) plus more showers this morning. Consequently, I’m above average- not just for September itself (5.52 inches) but for the year by about the same margin you folks are below average!

  13. Jo Ann Harris says:

    Very informative Thank you! I’ve been looking for in-depth weather data like this, and for someone to overtly talk about the rain deficit in the PNW. The mountains look so bare, and my garden is dry. At what point do we start using the “D” (for drought) word?
    PS. No doubt you were here all along, and I just finally clicked the right link.

  14. W7ENK says:

    So Ken, you were saying last week how crazy it was that the models were showing a tropical storm hitting California?

    Yeah. Crazy.

%d bloggers like this: