Winter 2017-18 Thoughts

Monday, October 30, 2017

Last winter was a crazy one as we all know.  4 freezing rain events and 4 snow events down here in the city and it was the coldest winter in 20+ years west of the Cascades.  Of course we had the biggest snowstorm in years in early January too…who can forget that evening?

Mark Ice_FreezingRainStorms This Winter

It appears we have another weak “La Nina Winter” on the way.  That can give us a few hints, definitely not a forecast, but what direction our winter might be “weighted” toward as last year.  In fact much of this info is a repeat from what I posted last fall.  I’ve spent some time looking at past La Nina episodes and what happened here in the Pacific Northwest.  I based all my graphics/research on a weak event.   Right now the Oceanic Nino Index (or ONI) is on the edge of NEUTRAL or WEAK La Nina category, which means the average of the past three months is right on the edge of “La Nina conditions”.  Once October is added in and July subtracted in a few days, we should be into the WEAK category.

LaNina TheBasics


Model consensus says we’ll likely be in a WEAK-MODERATE category during this upcoming winter.  Here’s the latest plume of ocean/atmosphere models:


Typically in these winters there are 3 effects observed to varying degrees:

  1. The north Pacific jet stream tends to be more “wavy” which means there is more of a north & south component to the jet instead of travelling straight west to east
  2. There is increased tendency for blocking somewhere in the east Pacific
  3. As a result there is sometimes more interaction of the cold Canadian air to the east and Pacific moisture with the jet stream weakening dramatically at times too.


Likely Effects This Winter in Our Area:

1.  Rainfall

I think it’s unlikely that we’ll have a drought winter; but far more likely precipitation will be above average.  La Nina winters in the Pacific Northwest are dominated by a strong jet bringing frequent disturbances across the region, interspersed with sudden ridging or northerly flow.   Then it’s back to the westerly flow.  For this reason they tend to be wet.  It’s likely the #1 most noticeable event in these winters.

1a.  Flooding

This actually goes with the rainfall.  For obvious reasons we tend to have more flooding events in winter due to the wetter weather.

2.  Mountain Snow

LaNina SnowMtHood

Lots of precipitation and cool weather systems = plenty of mountain snow.  This is probably the #2 most likely event.  10 out of 15 weak-moderate La Nina winters have brought above normal snow to ALL elevations in the Cascades.  This happened last winter with well above normal up high and on the lower slopes.  Somehow Government Camp ended up right AT average though.   Note that there CAN be a bad year, but it’s quite rare…see 2000-2001 below.

LaNina SnowMtHood2

3.  Foothill Snow

This happened in several of the past La Nina winters…significant snow to lower elevations (1,000′-2000′).  This MAY happen again if we get a succession of cold and wet systems coming in from the west and northwest.  Of course these are the same systems that give forecasters headaches because then snow it quite close to the Valley floor multiple times during the season.  News people get really excited about it too.

For you folks that live in the western Gorge…interesting to note less freezing rain in La Nina winters isn’t it?  More on that below in the “Portland Snow” section.

4.  Wind Storm

We are overdue for a regionwide major windstorm here in the Pacific Northwest.  The last BIG one was December 1995.  That’s 22 years ago!  14 years before that we had the major November 1981 storm.  It’s interesting that all those La Ninas from 1950 to the mid 70s had a wind gust of 60+ mph at PDX each time!  Not as frequent since that time though.

5.  Portland Snow/Ice

LaNina Portland Snow

This one is tough.  Anyone who says a La Nina winter means lots of snow in Portland is mistaken.  Average snowfall in weak-moderate La Ninas DOES go up a bit, but not a dramatic increase.  What I find interesting is only ONE La Nina in the last 30 years has produced a major snowfall here in Portland…last winter.  Of course you couldn’t say the same thing about 1989 down the Valley and up into Washington, but I’m just talking about right here in the metro area.   I should point out that the “cool/wet” La Nina winters sometimes produce little freezing rain because we don’t get as many inversion episodes to our east, which means less east wind in the Gorge.  We need that for a good ice storm either in the Gorge OR in Portland.  Of course the setup last winter was perfect for ice storms, the most I’ve seen in one winter in my career.  So lower confidence on this one.

7. Gorge Wind

Most La Nina winters tend to have less east wind through the Gorge during the winter season.  That’s because the strong easterly flow is mainly caused by stagnant high pressure sitting east of the Cascades during slow weather periods (upper-level highs overhead or split flow patterns).  During winters (like 07-08) we don’t get long periods of inversions due to frequent passage of cold fronts and low pressure centers.  I remember the winter of 98-99 (or maybe it was 99-00) was real quiet out in the Gorge too.  That said, when we DO get a big blast of cold air, we can get very strong easterly flow during the cold spell if a warm system approaches from the southwest.  Again, as with the freezing rain, this didn’t work out last winter.  It was a big east wind winter.


The elephant in the living room I suppose is the fact that our winters are gradually warming, and snow in Portland is definitely more rare than it used to be when we look back more than 20-30 years.  Snow each decade since the airport observations started about 1940:


And downtown records that go back to the late 1800s.  The low spot in the 80s is missing some data…it should be about 15″ higher:



We have always been in a marginal snow climate, but now warming temps are cutting off even more of the winter snow.  Every few winters we get 1 good snowstorm and we all remember that event.  We won’t forget the snow storm from January for a long time!  And remember 2008-2009’s record snowiest December ever?  It only went on for 10 days or so, then not much happened the rest of the winter.  That’s how it works here most of the time.

We’ll see how the winter turns out…my money (again) is on “wet” and “Cascade snow”, but I’m not sold that we’ll see anything other than a minor snow and/or ice event or several of those.

Chief Meteorologist Mark Nelsen


1. List of ONI values by season (Historical La Nina & El Nino Episodes)

2. Latest MEI discussion by Klaus Wolter

3. My presentation at Oct. 2017 AMS Winter Weather Conference…LOTS of graphics!

30 Responses to Winter 2017-18 Thoughts

  1. Whatcom County is forecast to get Fraser outflow winds later this week. Not supposed to make it down here, but snow levels are still gonna be around 1K feet. If it were 3 weeks later, I’d probably be expecting snow at my house. Here’s hoping this setup repeats in the not-too-distant future.

    • NWS now has the s-word in my forecast for tomorrow morning. My feeling is it probably won’t happen (and even if it does it’s just going to be flakes in the air, no accumulation), but exciting to see such wording so early in the season.

      • Roland Derksen says:

        Snow has been seen here mixing with the rain since 3pm. The last time I checked my thermometer was reading 37F. We’ll probably see the precipitation wind down over the next few hours, but if we get an intense shower, it could be all snow this evening.

  2. Nahtalkin says:

    Nora told Mark she got stuck in a shower today. Wonder how she got out.

  3. High Desert Mat says:

    Job security Mark. Anyone can forecast Portland weather. Just say it’s going to have rain or showers everyday and you’ll be 80% correct for the year! We need this variety of weather to keep you guys honest lol. Mark, we love you, you know I’m playin.

  4. Tom McCurley says:

    I was wondering why our apps on our phone keeps giving us bad air quality readings every one says the air is good

  5. Cliff Watkins says:

    Well done, Mark…..Lots of work for you…

    • JohnD says:

      “THE” Cliff Watkins!? ‘Guess I really am in a time warp! ‘Hope all is well! ‘Always enjoyed your forecasts!

  6. Nahtalkin says:

    The best part about winter weather for me is we won’t know what it’s going to be until it gets here. Winter is my time.

  7. gidrons says:

    I see point 5 Portland Snow/Ice and point 7 Gorge Wind.
    What happened to #6?

  8. Andy says:

    First frost in Albany, OR. Some years didn’t see first one until mid November.

  9. Longview 400 ft says:

    Low of 32 this frosty morning. White all around.

  10. Roland Derksen says:

    A chance of seeing snow here as early as this Friday.I’ll be keeping my eyes open for it.

  11. Patchy frost overnight here. First one I’ve recorded in October since moving to the island.

  12. Paul D says:

    The statistic you didn’t list is how many days the schools were closed last year! 🙂

  13. Boydo3 N. Albany says:

    Nice summary! Climate trends are well averaged, the deck is shuffled, but the wild card of weather is yet to be played.

  14. Ellen Wallace says:

    question: Columbus Day storm – La Nina-ish or El Nino? and the winter of 1968-69 and ’70-71 or was it 71-72 (?) which was that? none of this naming stuff had been invented. Looking forward to an interesting season…Thank you!

  15. JohnD says:

    Sort of a buzz kill that there is not more bullishness happening. But I get it. A lot seems to depend–generally speaking–on how the strength (or lack thereof) of the current La Niña episode plays out. And–of course–that no two are ever alike! Thanks–as always–Mark!

  16. Last big windstorm was 2006, Hanukkah Eve windstorm. Had the Highest wind speed ever recorded at SeaTac (69 MPH) and right before 1995 storm was the historic Inaugural Day Storm (1993). Also had the major storm in March of 1999.

  17. Maxineg small says:

    Marsha needs to get rid of that leather leather skirt and cover her knees

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