Weather Action Picks Up…For a Few Days

8pm Tuesday…

I’m still keeping a close eye on heavy rain expected on Friday.

An “atmospheric river” will set up late Wednesday through early Saturday along the West Coast.  An “AR” is a narrow channel of tremendous water vapor transport through the atmosphere.   From the tropics or subtropics into the middle latitudes (where we live).  For this reason they are often referred to as a Pineapple Express.  They can easily transport double the volume of the Amazon River overhead!  They have always existed, but the naming is relatively new (within the past 20 years).  You can read more about them on the AMS website.

Atmospheric River Rain Explain

I think the three day forecast summarizes things well:  light rain showers tomorrow, regular rain Thursday, then heavy rain Friday

3 Day Forecast Graphic Portland

Of course the big question is “will there be enough rain for flooding?”.  We still don’t know the answer; partly because models are trending DOWNWARD on rain totals now through Saturday.  First, widespread river flooding on the Willamette or Columbia river systems is very unlikely.  That’s because reservoirs are at their winter flood control minimum levels.  In fact Detroit Lake is 20 feet BELOW that level!  The entire storage system for the Willamette River is basically “empty” with respect to flood control capacity.

willamette

Unregulated smaller rivers are still at risk of course and then there’s the situation with “urban and small stream flooding”.  That happens when we get a long period of moderate rain or a few hours of intense rainfall.  The GFS model says forget about both.  But the ECMWF is still going gangbusters for a major rain event central/north/west metro Friday.  Check out 6 hour rainfall total just for 10am-4pm Friday centered right over the metro area

ecm_10am-4pmFri

It thinks we’ll see 3″ or so in a good part of the metro area in just 24 hours ending 10pm Friday night.  This would be a big deal and cause widespread flooding issues

ecm_24hrsending10pmfri

BUT, other models are somewhat/significantly drier.  Predicting exact location and intensity of atmospheric rivers is tough.  Models probably won’t settle down for another day or so.

To summarize:

  • We have a lot of rain on the way; definitely the wettest so far this season.
  • I’m confident we have at least two inches rain on the way for the metro area tomorrow through Saturday morning
  • We could see far more than that, but still don’t know yet
  • If you live in a location that has seen flooding during heavy rains in the past, pay close attention to the forecast
  • IF we get some flooding, it will be Friday or very early Saturday.  Don’t worry about tomorrow or Thursday.

Another item of interest; we go right back into split flow and upper-level ridging for Christmas week.  This isn’t a turn toward a typical wintertime wet weather pattern.  Just a blip in an unremarkable wet season so far.

Chief Meteorologist Mark Nelsen

 

34 Responses to Weather Action Picks Up…For a Few Days

  1. Roland Derksen says:

    My heaviest ever one day amount of rain was back on December 25, 1972. Around 4.30 inches. This one’s going to have to be really special to beat that.

  2. Jake in Gresham says:

    Just got over the half inch mark here since last night. At about 11pm it was 0.25 inches. So not too bad a pace.

    Starting to see puddling in the yard. Stay safe out there folks.

    But stay safe out there people. The night before I made it to a green light and crossed the intersection to a road corner full of car debris (half a bumper just laying there with a headlight attached).

    Thank goodness it was a two lane road I swear.

    The night before that a truck came tearing across 2 oncoming lanes into the left lane next to me completely ignoring the median. This put them right next to me (in the right lane) and they then proceeded to take my lane without checking their blind spot. Almost put me into a streetlight. I had to go into the bike lane, swerving around him and then into the left lane.

  3. Jason Hougak says:

    So much for the 1-2’ of snow in the Oregon Cascades, most locations look like they only picked up 4” and temps now have creeped above freezing. The Washington Cascades look to get hammered. The NWS 🙄

  4. K says:

    Congrats to Seattle for getting the event again, I guess?

    • Joshua Lake Oswego says:

      Unfortunately, the writing has been on the wall for a couple of days. Now that we are within a high degree of forecast certainty, it is essentially certain that this is going to be a mainly coastal Oregon and all of Western Washington event. We get the slops. Most of the metro area and locations south will be lucky to get 2” from Wednesday – Sunday. That would have been worse than a worse-case scenario not too long ago.

  5. Joshua Lake Oswego says:

    Christmas Day into the 26th is trending wet for us and a nice dumping for the Cascades. Reasonably low snow level too.

  6. Grizzly Bear says:

    Been below freezing here since Sunday afternoon, last night a low of 9 degrees and highs in the 20’s. Kamiah Valley is a Christmas Postcard of snow covered beauty. Sure don’t miss the soggy wet western Oregon in winter.

  7. Joshua Lake Oswego says:

    It’s looking like a lot of us are going to be SE of the hose and our totals won’t be too impressive. The ECMWF is the last hope.

    • Joshua Lake Oswego says:

      Euro backing down as expected, but still very bullish. Honestly, the Euro has been trash for a while. ALWAYS optimistic with precipitation and cold for our area.

    • W7ENK says:

      C’mon, you know as well as I do (and everyone else who’s ever experienced an AR event here) that these things whip back and forth — literally — like an uncontrolled fire hose, hence the analogy. It swings to our North, it swings to our South, it’s pointed right at us… but everyone gets wet.

      The event technically hasn’t even started yet and I’m already at a quarter inch since midnight. I’m right across the river from you in pretty much straight line with most everything that hits us, therefore I know we both get about the same, so for the love of all things, please stop whining.

  8. Kyle says:

    Warmth? Fail! Forecasted high of 49F and a low of 42F tonight is a total bust. It never even got to 40F all day. It remained mostly at 34F and briefly spiked at 39F before light drizzle brought it back down to 37F.

    Most of the day was frosted till about noonish.

  9. Kyle says:

    Warmth? Fail! Forecasted high of 49F and a low of 42F tonight is a total bust. It never even got to 40F all day. It remained mostly at 34F and briefly spiked at 39F before light drizzle brought it back down to 37F.

    Most of the day was frosted till about noonish.

  10. WEATHERDAN says:

    My forecast for Thursday 12,19,2019-12,21,2019 is as follows. KEUG 1.5″, KSLE 1.75″, KPDX 2.33″. Some spots may locally receive 2.75″ in SW Washington, but predictions of 5.5″ inches inland make me think somebody is smoking some of the good stuff. Peace and Merry Christmas.

  11. Mr Realist says:

    Christmas week is looking mild kids, enjoy 😎😎😎😎😎😎😎😎

  12. runrain says:

    Sung to the tune Let It Snow:

    Well, the models are all a-runnin’
    ‘Cause we think a storms a-comin’
    But we all know it ain’t gonna snow
    Let it go, let it go, let it go

    It’s winter in the west, for sure, now
    We all want a brand new snow plow
    But the split flow starts to grow
    Let it go, let it go, let it go

    When we finally say goodnight
    After model riding is all done
    And it’s time to give up the fight
    The winter just won’t be fun

    A storm is out in the ocean
    But the Rex Block shows no motion
    All sun, no wind, no snow
    Let it go, let it go, let it go

    • Evan -- Cedar Mill says:

      Good one!

    • boydo3 says:

      That’s a good one!
      For Mr Realist here one as sung to the tune of “we wish you a Merry Christmas”..
      We wish you a merry wishcast
      We wish you a merry wishcast
      We wish you a merry wishcast
      And a sack of old coal.
      🙂

  13. Andrew says:

    Am I seeing things or does GFS want to drop a couple inches of snow over Eugene and Salem on Christmas day??

  14. Mr Realist says:

    So exciting……………….

  15. tim says:

    So just a bump in the road before we resume back to our new normal dry/warm winters, ok for a minute there i thought things were turning around for once where’s my head lately, geez.

  16. W7ENK says:

    And Mark, 20 years ago was December 1999. I remember hearing the term “Pineapple Express” from when I was a kid in the ’80s, which, as much as I hate to admit, was pushing 40 years ago. And that came from my parents, who grew up in the 50’s and 60’s, which was like… 80 years ago… or something.

    We’re all older than we think. 😥

  17. W7ENK says:

    Hold onto your butts…

  18. Jody says:

    Any chance of snow in the Gorge/Hood River in the next couple days? It’s soooo cold. PS- love this weather blog!, Thank you!

  19. Mokihana says:

    Thanks so much for this, Mark!! I really love how you’re keeping us informed.

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