Monday, October 8th…
Every fall people ask me what “this winter will be like” or “I’ve heard it’s going to be a bad winter”. By the way, I’ve NEVER had a person say “I’ve heard it’s going to be an easy winter”. Apparently most of us are quite cynical and expect the worst.
I don’t put out a “winter forecast” each fall. That’s because the few forecasts I see are often wrong and seasonal/climate forecasting has a long way to go before we say we can “forecast” a winter. So we’ll just call it “my thoughts” for the upcoming winter since we can at least glean a few tidbits.
First, a summary of the past 3 winters:
2017-2018 Last winter was a “La Nina” winter which means for the 2nd consecutive year the tropical Pacific Ocean was cooler than average. For meteorologists (and you) it was a “slow” winter; warmer & drier than average. We had a brief snow/ice event at Christmas and then one fun week in late February with snow and that was it.
2016-2017 This was the first “La Nina” winter; it was crazy, wild, & cold. There were numerous ice & snow storms in the Portland metro area, Gorge, & Eastern Oregon.
2015-2016 Three winters ago we endured an incredibly wet & wild December. Remember all the mudslides and flooding? Otherwise that “El Nino” winter was quite mild. By the way these images are from my yearly winter recap presentation.
As I mention above, there is still a LOT we don’t know about our climate and seasonal shifts in our weather. It’s hard to believe, but this will be my 28th winter forecasting here in NW Oregon (started forecasting professionally in October 1991). Typically we focus on the La Nina/El Nino oscillation across the tropical Pacific and what that means for northern hemisphere winters. That is still the case, but a few other factors are likely playing into our winters including this one…a weakening polar vortex: https://www.eurekalert.org/pub_releases/2017-09/pifc-wce092217.php That research, published just a year ago, suggests there have been increasing outbreaks of cold polar air farther south as the arctic warms. Interesting eh? Of course down here in the Pacific Northwest the issue is WHERE the cold air dumps south. For example, that first La Nina winter (above) we had cold air come down to our east quite frequently (a frozen Eastern Oregon). Then last year (2nd La Nina winter) something was different for some reason and the cold air stayed farther east. We had a warmer/drier winter during a La Nina year! So each winter is different and lots more research is needed.
At this point NOAA is expecting this to be an El Nino winter; most likely a weak to moderate event. As of last week the tropical Pacific has just crossed into El Nino conditions in the central part of the basin. Models are in good agreement we’ll slip into a solid El Nino event the next few months. Anything above 0.5 is considered 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:
But during most (not all!) 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.
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 (like in 2015-16). Both 1982-83 and 1997-98 (strongest since 1950) both featured near or above normal rainfall even up here in Portland.
Compare that to 2009-2010, the traditional El Nino signature…
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 8 El Nino winters:
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 and the mild winter resumed.
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 is centered east of the Cascades. Notice the most easterly wind the past few years was during the El Nino event in 2009-2010. 2015-16 was also a big east wind year.
TO SUMMARIZE ALL OF THIS:
- Most likely we have a generally milder and drier winter than average on the way. Or at least milder temps with normal rainfall if we get lucky.
- Long periods of cold/snow are unlikely this year
- We could easily see a snow or ice storm at some point
- Widespread regional flooding is unlikely this winter
- Expect a bit more east wind than normal this year
SKIING & MOUNTAIN SNOWPACK
> EL NINO WINTERS ARE RARELY SKI “DISASTERS”
The phrase “EL NINO” often strikes fear into the hearts of Northwest skiers and is a somewhat deserved reputation. In these winters, we tend to see warmer and drier weather than average across the northern half of the Pacific Northwest as mentioned above. As you’ve also likely heard, California in many of these winters gets slammed by lots of stormy/wet weather (but not all!). Here is a look at the last 7 El Nino winters combined…the precipitation anomaly. Warm colors mean drier than average, cool colors = wetter than average.
And temperature anomaly for the same years, a clear signal for warmer than normal:
So let’s take a look at Cascade snowfall during the 24 El Nino winters we have seen since the early 1950s at Government Camp. Average yearly accumulation is 270″ (click for full-size)
That’s not good news. A few thoughts:
- EVERY EL NINO SINCE 1970 HAS PRODUCED BELOW NORMAL WINTER SNOWFALL AT 4,000′ ON MT. HOOD.
- 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 be 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. Mt. Hood Meadows is up at the 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:
A few thoughts on that graphic:
- Snow accumulation increases dramatically as you go up in elevation. Looks like that extra 1,500′ or so almost always doubles total yearly snow (every year). Much of that is in “shoulder seasons” of November and mid-March/April/May, I suppose when it’s too warm down at Gov’t Camp.
- El Ninos are more reasonable at a higher elevation. That’s because we tend to be warmer in El Nino winters with warmer storms.
- 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.
- 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:
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.
Sorry this has been such a long read, but hopefully you have a little better feeling for what we might see during this upcoming winter.
Chief Meteorologist Mark Nelsen