It’s been a beautiful autumn across the Pacific Northwest, at least if you love colorful leaves.  Trouble is, I haven’t been able to get out much due to a long-winded car repair fiasco.  But just from the vantage of Portland, I’ve noticed brighter colors than usual – and the colors have peaked a week or two earlier than in recent years; i.e. the middle of October instead of near the end.  By Halloween, most of the vibrant colors were already gone.

 

The weekend before last, I made my annual pilgrimage to the Winter Weather Conference at OMSI.  It’s the biggest weather nerd event of the year in Portland, and attracts hundreds of attendees every year.

There were several excellent presentations this year, beginning with a 9am project by University of Washington professor Cliff Mass.  He covered two interesting topics:  first, the return of ‘The Blob’ off the PNW coast and how it gave us unusually warm summer nights.  Second, the link between wildfires, offshore flow, and climate change.  Local KPTV meteorologist Mark Nelsen continued his annual tradition of reviewing last winter – “Boring As Fork” for the first two months, then a historically cold February and early March.

 

The three 2019-2020 forecasts were given by NWS meteorologist Tyree Wilde, hydrologist Kyle Dittmer, and KOIN a.m. meteorologist Kelley Bayern.  I’m not going to discuss the details here; their forecasts can be found on the [AMS website].  However, several key themes stuck out in my mind:

 

1. We’re likely headed into either an ENSO ‘neutral’ season, or else a very weak El Niño.
2. Neutral years tend to be wetter than normal, with an increased chance of Pacific windstorms.
3. Neutral ENSO years tend to see more low-elevation snow in the Portland Metro area, but near-normal snow in the Cascade mountains.
4. The official NOAA/CPC forecast is for above-normal temps across much of the continental U.S., especially the western 1/3 of the country.

 

MY THOUGHTS.

 

I’m not going to step out and give an “official” winter forecast.  Two reasons:  one, there’s still a lot of uncertainty with any winter outlook, especially with regards to snow or ice in the lowlands of Western Oregon & SW Washington.  (More on that in a moment.)  Second, forecasting in neutral years is always a bit of a wild card.  Some years we’ve had extended periods of mild weather, others we’ve seen a lot of cold Arctic action near the West Coast.  And sometimes, we get a combination of both:  the neutral winter of 2013-14 featured the coldest arctic blast of the decade, but also some of the longest periods of ridging & inversions I’ve ever seen.

 

Furthermore, the past two winters have largely defied the general ENSO theme.  The 2017-18 season was La Niña, but it had long periods of boring weather with only one major cold pattern in late February.  (On the other hand, that one week of cold northerly flow produced multiple snowstorms in the Portland Metro area.)  In contrast, the 2018-19 winter was El Niño, yet featured a month-long period of very chilly troughing in February and early March, including some of the latest-season snow cover east of the Cascades that we’ve seen in modern history.

Point is, even a strong warm or cool signal in the tropical Pacific is not a guarantee as to what actually happens.  In a neutral year, the uncertainty is even more enormous.

 

The most recent neutral years were 2013-14, 2012-13, 2003-04, 2001-02 and 1996-97, according to the ONI index.  As you might recall, both January 2004 and February 2014 saw major snow events in the Portland metro area, as well as very deep snowstorms in the Columbia Gorge.  But the 2012-13 and 2001-02 seasons were complete duds for the city.  I don’t seem to recall 1996-97 (my freshman year of high school in The Dalles) to be very active either, though the Gorge DID get a wet snowstorm before Thanksgiving that year.

 

Here are the precipitation and temperature anomalies for those five December-February seasons, courtesy of NOAA’s Climate Division Data :

Hmmm…dry and warm for California and the Southwest, but cool and wet for the Northwest.  Also some major arctic air events in the Northern Plains if this is to be believed.  All of this seems to vibe pretty well with the forecasts from the Conference, which call for an active/stormy winter with a good chance of snow in the lowlands.  I should also point out that none of the past five neutral winters were particularly bad for Cascade snowfall; though 2013-14 started out looking like it was going to be.

 

That said, the official NOAA forecast  for this winter is warmer than average along the West Coast:

This is why I’m not confident at forecasting winters.  There are too many variables still at play including, crucially, the position of the jet stream.  It seems as though the jet has experienced more periods of “amplification” in recent years.  This results in longer periods of continuous cold/warm/dry/wet, than we’d see in a more normal, “zonal” jet configuration.  The unusually dry past 2 weeks, was itself a result of a highly amplified ridge along the West Coast.

One intuitive thought.  Three times this autumn, we’ve seen this ridgy pattern back off to the west for a few days, allowing very cold Canadian Arctic air to surge southward into eastern Oregon and Washington.  This then affects Portland via the chilly east wind coming through the Gorge.  Despite being only 3.4 degrees F below average, October 2019 was the coldest October at PDX in 70 years!  It was the coldest October in 71 years of record-keeping at The Dalles Airport, as well.  There are two things to take away here:  first, we don’t usually see big cold departures in October in the Pacific Northwest.  Second, the anomalously cold October of 1949 was followed by one of the worst winters in the past century, with subzero temps even in Portland by early February 1950.  (I think The Dalles dropped to -25F.)

We don’t know if the current amplified ridge, or another ridge later in the season, will retrograde in a similar fashion.  But if it does, then we’d likely see the Gorge and parts of northwest Oregon thrown into a cold wintry weather scenario.  For now, though, the safe bet is to plan on a little of everything for this winter:  rain, some wind, flooding/mud, mountain snow, and maybe some low-elevation snow and ice.  And the way the past few years have gone, I wouldn’t be surprised to see an extended dry spell with inversions and cool east wind at some point.

A final word of warning:  If anyone on social media, or even a weather anchor on TV, claims that there’s going to be a “big snowstorm in early February” or “turning cold just before Christmas,” please ignore them.  There’s no way we can forecast specific weather events 4 or 6 weeks in advance, not even if the ENSO or other climate indicators suggest we’re in for an active season.  There has already been at least one article from a local news station, suggesting that we have a cold snap on tap “at some point in early December.” We’re never going to be able to see signs of a coming pattern shift, more than 10-12 days in advance.  And even then, it’s dangerous to make too much out of long-range model maps.  It’s perfectly normal to see some sort of cold air pop up 10 or 11 days away on the map, only to have following model runs yank it away and give us more of the usual winter rains and fog.

In the event that a cold episode DOES appear imminent, I will post here explaining why I feel confident about it.

But for now:  Grab your magic ‘8 ball’ for this winter, because it might be more reliable than any official outlook.

Karl