WINTER 2015-16 EL NINO

We tend to see a changed jet stream during El Nino cool seasons.  Typically the Pacific jet stream flows generally west to east and runs into the northern half of the USA West Coast.  Thus the heaviest winter rains tend to fall in the Pacific Northwest, as opposed to California:

MarkElNino_PacificNorthwestEffects

But during most El Nino winters we see the southerly part of the jet stream suppressed farther south, partly due to a stronger area of low pressure in the eastern Pacific.  Actually the subtropical jet is pushed farther north than normal, heading into California.  At the same time we tend to see more episodes of upper-level high pressure over the western part of Canada.  This shunts arctic air farther east than normal, giving the Northern Plains a warmer than normal winter.  Meanwhile that wet (and warm) westerly jet running into California gives them a wetter than normal winter.

MarkElNino_PacificNorthwestEffects2

MarkElNino_PacificNorthwestEffects3

Notice the Pacific Northwest is a mix of weather.  The northern part is strongly influenced by the upper-level high, the southern part (southern Oregon) often gets in on the edge of the California moisture action.  As a result, southern Oregon ski areas and basins receive normal or even above normal precipitation.

It’s important to point out that though many El Nino winters follow this pattern, sometimes they don’t .  No guarantees!  It has also been noted that in the very strong El Ninos, the heavier precipitation appears to make it farther north.  Both 1982-83 and 1997-98 (strongest since 1950) both featured near or above normal rainfall even up here in Portland.   1983

1997

Compare that to 2009-2010, the traditional El Nino signature…

2009

What about extreme cold during this winters?  A bit of a mixed bag because even in a mild winter it only takes one 4 day arctic blast to trash your plants.  4 out of 15 Strong/Moderate El Nino’s had a significant outbreak of “arctic” air.  If you take just the STRONG events, only one in the past 40 years has given us a days-long arctic blast event.  That was 2009-2010.  We hit 12 that year!  So the likelihood of a long arctic blast is quite a bit lower than normal, occurring in only 27% of moderate/strong years.

MarkElNino_ColdPDX

Of course what everyone really wants to know is…will it snow at MY house this winter???

A misconception to get rid of is that a warmer/drier winter means no snow in the lowlands.  Not true at all. El Nino does NOT mean NO SNOW.  Check out the last 6 moderate/strong El Nino winters:

MarkElNino_SnowPDX

We saw decent snow storms in January 2007, January 1998, & February 1995.  And who can forget the fiasco in late December 2009…the surprise (crappy forecast) snow event that gave us the worst evening commute in many years!  There is one common theme in each of these events; they all lasted just a short time, then the mild winter resumed.  I distinctly remember shoveling feet of drifted snow (Corbett) in January 1998 under a “hot” 50 degree sun once the east wind stopped.

To summarize…

It’s unlikely we have a snowy/cold winter ahead, but it’s quite possible we get some sort of freezing rain or snow event at least once during the upcoming winter.

One more point…one of the most hated parts of winter for part of the metro area is the cold east wind.  The Columbia River Gorge produces what we call a “gap wind” when high pressure east of the Cascades sends air rushing through the sea-level gap through the mountains.  The east side metro area near and south of the Columbia River is fully exposed to the wrath of this wind.  It begins to appear in late October and reaches a peak from November through February.  Then the wind disappears in early March as the seasonal westerlies begin.

Does El Nino mean more or less east wind?  Based on my experience, it’s generally a case of MORE east wind.  That’s because during El Nino years, we have a split or blocked jet stream more often, leading to more time under surface high pressure.  And much of the time that’s centered east of the Cascades.  Notice the most easterly wind the past few years was during our last El Nino event in 2009-2010.

EastWind

TO SUMMARIZE ALL OF THIS:

  1. Most likely we have a generally milder and drier winter than normal.  Or at least milder temps with normal rainfall if we get lucky.
  2. Long periods of cold/snow are very unlikely
  3. We could easily see a snow or ice storm at some point
  4. Widespread regional flooding is unlikely this winter
  5. Expect a bit more east wind than normal this year again

Here is a chart showing some of the data I used while researching past events:

Capture

 

Now let’s talk skiing/snowpack and get two big issues out of the way:

  1. IT’S EXTREMELY LIKELY THAT THIS WINTER WILL BE BETTER FOR SKIING THAN LAST WINTER
  2. EL NINO WINTERS RARELY LOOK LIKE LAST WINTER; THEY GENERALLY ARE NOT “DISASTERS”

Basically we hit bottom last winter, seeing the worst ski conditions in decades, and ANY winter should be better than that right?  That’s the working theory for this winter…

The phrase “EL NINO” often strikes fear into the hearts of Northwest skiers and is a somewhat deserved reputation.  El Nino is a warming of the tropical Pacific Ocean.  All that extra heat causes changes to ocean and atmospheric circulations, affecting weather across the globe in different ways.  As of now, the Oceanic Nino Index (ONI) is at a huge +2.3 deg C.  That puts this event right up with the “Super Ninos” in 1982-83 and 1997-1998.  This is a big one.  IF the current conditions were to continue for the next 5 months (a big IF), this could be the strongest on record since 1950.  But it isn’t for now and at least one model, the CFS, implies this event will peak in the next month or two.

Capture

Regardless, this is a “Strong” El Nino and it’s here to stay for this coming cool season.  In these winters, we tend to see warmer and drier weather than average across the northern half of the Pacific Northwest.  As you’ve also likely heard, California in many of these winters gets slammed by lots of stormy/wet weather.  Taking all moderate/strong El Nino winters since 1950, here is the average precipitation anomaly from November-February…pretty dry:

Moderate_StrongElNinoYears

And temperature anomaly for the same years, warmer than normal:

Moderate_StrongElNinoYearsTemp

 

 

So let’s take a look at Cascade snowfall in the 23 El Nino winters we have seen since 1950 at Government Camp, where average yearly accumulation is 270″ (click for full-size)

ElNino_GovernmentCampSnow

That’s not good news.  A few thoughts:

  1. EVERY EL NINO SINCE 1970 HAS PRODUCED BELOW NORMAL WINTER SNOWFALL AT 4,000′ ON MT. HOOD.
  2. ONLY A FEW YEARS ARE REALLY BAD, MOST JUST HAVE LESS FREQUENT SNOWFALL AND MORE RAIN/SNOW EVENTS.

There is a downward trend as well through the period, although 23 data points is a pretty small sample!  Do you notice the events in the 1960s seemed to do just fine for snowfall, but post-1970 or so things have gone downhill at bit?  It may that a very gradual warmup in the Cascades has produced more warm storms (rain vs. snow) at that elevation.  Notice that I am focusing on the 4,000′ elevation.  That’s because monthly snowfall data is very hard to find.  Records are also taken at Timberline and Mt. Hood Meadows, but aren’t generally publicly available.

Mt. Hood Meadows issued a nice media release earlier this summer that included total winter snowfall at that 5,400′ elevation.  So I plugged in those numbers to see how things vary vs. Gov’t Camp.  Those records only go back to 1982:

ElNino_MeadowsvsGov'tCampSnow

A few thoughts:

  1. Snow accumulation increases dramatically as you go up in elevation.  Looks like that extra 1,500′ or so almost always doubles total yearly snow.  Much of that is in “shoulder seasons” of October/November and mid-March/April/May, I suppose when it’s too warm down at Gov’t Camp.
  2. El Ninos are more reasonable at a higher elevation.  That’s because we tend to be warmer in El Nino winters with warmer storms
  3. At higher elevations a few El Nino winters have actually been snowier than normal.  Another reason to not totally freak out.  You will likely need to spend more time this coming winter on the higher parts of your favorite resort.
  4. 1982-83 is a weird one, Gov’t Camp was well below average yet Meadows was above.  That MAY be because the best snow was in the spring when it was getting too warm down below.  Not sure since I don’t see the monthly data.

That brings up a good point…total snowfall for the season doesn’t matter as much as what happens during the important winter months of December-February when most of us ski/snowboard.  Here are the Gov’t Camp numbers for just that 3 month period during El Nino winters:

ElNino_GovernmentCampDEC_FEBSnow

Thoughts:

  1. Snow during the important December-February period is below normal during every El Nino since 1970.  Some of those years are way below normal as well.
  2. The moderate/strong El Nino years don’t tend to be the “disaster” years (except for 1991-1992)

 

I think I can dispel one myth that I’ve been passing along over the years.  That El Nino winters often start with a “bang”…great snowfall right away in late October/November that then peters out as we get into late winter.  Apparently that’s not true.  Out of the last 10 moderate/strong El Ninos, 5 saw lots of snow by Thanksgiving, 5 did not.  Doesn’t seem like a very clear signal to me.

You may notice I didn’t mention the warm “blob” of water in the Eastern Pacific or the very warm PDO right now.  Those are both long stories for another time, but I don’t believe either one helps the snow situation for this coming winter.  I didn’t see any reason to pile that onto this posting!

Chief Meteorologist Mark Nelsen

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