Cooler (And Normal) December Weather Is Here To Stay

December 3, 2021

9pm Friday…

December arrived with record warm temperatures across the region. Wednesday (the 1st) was the warmest December day we’ve seen in Portland since 2015! These are just a few of the records set that day. Notice several spots in eastern OR/WA set all-time December high temperature records.

Cliff Mass (UW) in his blog called this the 2nd great Northwest heatwave of 2021. By that he means that many areas east of the Cascades observed “heat” just as anomalous as the June event; 25 degrees or more above average in spots.

We cooled off nicely today after a cold front passed through yesterday morning. Highs today were back in the 40s along the I-5 corridor…much more seasonal.

What’s ahead?

The mild/warm westerly flow in the upper atmosphere is changing to a setup where cool troughs dig down from the northwest, passing through our region. Each one should spin up some sort of wet system. So we can expect precipitation regularly over the next 7-10 days. Here’s the view Saturday

Then Monday; another trough passing by

Then a third next Wednesday

Looking farther ahead, to Monday the 13th, models GENERALLY have more troughing digging into the eastern Pacific.

In general this whole setup the next 7-10 days is cooler than normal. At this point I don’t see any surge of cold arctic air moving south, but it may be close at times. This chart shows things well. It’s the ECMWF 850mb temperature ensemble chart. It shows temperature (C) around the 4,000′ elevation for the next two weeks. Green line is the average of all 51 ensemble members. I’ve drawn the yellow highlight at 0 degrees.

Basically for pass elevation snow in the Cascades it needs to be at/below that yellow line. That’s the case most of the next two weeks…very good. Finally, we’re going to see a snow base develop in the mountains, and it’s not going anywhere this time.

Lowland Snow?

It’s that time of year! The next 2.5 months are primetime for snowfall in the lower elevations of NW Oregon and SW Washington. I’ve got a few thoughts on that. The pattern I’ve shown above CAN bring snow to the lowest elevations of the region, but right now it doesn’t appear to be quite cold enough to do that. Sure, late next week 850mb temps dip to around -6 or even -7 at 850mb. That means foothill snowfall for sure (1,500′ or higher). But it takes more than that to get any sort of widespread snow event to the valley floors. I’m not saying we won’t see snowflakes at some point in the next 10 days, but nothing really sticks out on the maps right now. Note there is almost no support for significant snowfall from ECMWF ensemble members in the next 10 days. This is for Aurora/Canby; I chose a spot in the middle of the valley to avoid low resolution modeling issues. Ignore anything beyond 10 days…it’s a crapshoot after that.

SUMMARY

  1. There’s no sign of a cold “arctic blast” the next 7-10 days. My exposed chicken coop waterline will remain on for now. Beyond that, the 15th and after? Who knows!
  2. I don’t see any sort of widespread snow/ice in the lowlands in the next 7-10 days. I haven’t put my snow tires on yet and don’t plan to for now. However, I would not be surprised to see flakes mixed in with rain at some point during that period. Or even a brief snow on the hilltops…maybe.
  3. It’s quite possible we see at least some partial ski area openings NEXT weekend, the 11th/12th

That’s it for now. Have a great weekend!


No Skiing/Snowboarding Yet, But No Need To Panic

November 30, 2021

9:30pm Tuesday…

Thanksgiving has come and gone, along with all that snow that fell last week in the Cascades. About a week ago the snow was between 6-18″ deep at the Mt. Hood ski resorts. But that is all gone now. Here’s the view at Mt. Hood Meadows base area yesterday morning; most of those patches are now gone.

And way up at 6,000′ at Mt. Bachelor’s base area

Having mainly bare slopes at these elevations IS unusual as we head into the first few days of December, yet not unheard of. Check out snow depth on November 29th each year at the SNOTEL site in Timberline’s ski area

It’s the lowest since 2008. In fact I still have the picture from a blog post on December 1st, 2008

What happened later that year? Well, it looked like this on December 23rd at my home near Corbett

Yep, a cold wave arrived around mid-month and snow started accumulating not only in the Cascades but down in the valleys as well. The Mt. Hood Test Site (SNOTEL) went from just about nothing in early December to just under 9 FEET of snow on the ground by New Year’s Day! Over 500″ fell that winter. Proof that things can change quickly this time of year. Mt. Hood Meadows put out a nice “scatter plot” graphic today. The image below shows how much snowfall they get each season vs. opening date. An average winter picks up around 450″ at that 5,400′ elevation. There DOES seem to be a tendency for lower seasonal totals with later starts, but not dramatic most years.

It appears that only 5 of the past 26 seasons have started this late (sometime beyond December 5th). 3 of those ended up with reasonable conditions, two not so much.

What’s ahead?

The reason it’s been so mild has been stronger than normal upper-level ridging over the West Coast. That’s sending lots of warm-ish storms inland just to our north (NW Washington flooding). That general pattern continues for at least another 7 days. Our 7 day forecast for Government Camp says no chance for skiing through at least the 8th of the month

This chart shows the 850 millibar temperature forecast for the next 16 days…from the European model. That’s temperature in Celsius around pass elevation around Mt. Hood. The green line shows the ensemble average, and I’ve put a yellow highlight at “0”. Anytime temperatures are near/below that line precipitation would generally fall as snow in the Cascades. Notice there is a change just beyond our 7 day forecast. IN GENERAL, models are expecting cooler conditions from that point forward, and they’ve been hinting at that general change for the past 1-2 weeks.

Other models are similar, so to summarize:

  1. This extremely low early December snow depth is unusual, but it has happened in the past
  2. There’s no reason (at this point) to believe this means a poor ski season or low snow year in the Cascades
  3. There’s good reason to believe we will see a pattern change, kicking the ski season into gear, about 7-10 days from now…maybe some skiing for the 2nd weekend of December!
  4. Don’t panic! Be patient…

Chief Meteorologist Mark Nelsen


Mild Weather & (Mostly) Good Travel For Thanksgiving Week

November 22, 2021

8pm Monday…

Most likely you experienced a mainly sunny weekend, OR a foggy/cloudy one. It all depends on your location because we saw the first seasonal “inversion” across the region. That’s when cool overnight air stays trapped in the valleys during the very long “winter” nights, along with moisture. The combo leads to persistent fog/clouds in some valley locations both east and west of the Cascades and it happened over the weekend, especially Sunday. This is a common feature of our climate from late November through late February.

Portland only made it to 46 yesterday and parts of the valley never broke out of the gray. Meanwhile east metro areas stayed clear with just enough drier Gorge wind keeping the clouds away. The Cascades remained sunny above the inversions too. In fact Central Oregon (above 2,000′) popped into the 60s today!

A cold front is approaching tonight and that’ll bring us with the usual steady rain turning to showers. This time a much colder airmass follows, along with strong WESTERLY flow into the Cascades. That should be very efficient at dumping lots of snow up there. 6-10″ is likely, on top of the 2-6″ on the ground at the ski resorts.

Of course that isn’t enough for Thanksgiving Weekend skiing, especially with the snow level headed WAY up the rest of the week. Lots of mild weather to wrap up November…

This mild weather pattern is caused by a “flat” upper-level ridge in the atmosphere; that’s warmer than average air over the western USA. Here’s the 500mb map for Thanksgiving Day

And then again NEXT Monday, the 29th…still mild

By the way, there are strong hints from our long range models that a turn toward more typical or even colder than normal December weather might show up about two weeks from now, but that’s WAY out there…

For now, expect lots of days in the 50s over the next week with little/no weather impacts on your Thanksgiving travel. I’ve covered the Cascades…snowy tomorrow through Wednesday morning, then much better Wednesday afternoon and pretty much clear through passes Thursday. How about the Gorge? No sign of cold air, but tomorrow’s snow WILL impact the Blue Mountains between Pendleton and La Grande

Coast Range passes will be all clear through the weekend, as will I-5 both north and south of us. Sometimes we see snow at I-5’s Siskiyou Summit south of Ashland this early in the season, but nothing significant is in the works for this long weekend.

That’s it for now, enjoy the mild Thanksgiving holiday!

Chief Meteorologist Mark Nelsen


Late November Weather Slowdown In Pacific Northwest

November 16, 2021

7pm Tuesday…

The first half of November has been very warm in the Pacific Northwest, 3rd warmest on record (first half of month) at PDX.

Now that’s partially due to a long-lived atmospheric river event late last week through Monday. That was a real doozy in Washington, not as extreme in Oregon. Huge rain totals with record flooding the past few days in SW British Columbia and NW Washington. Portland picked up just under 3″ out of the event Thursday-Friday, an excellent forecast by forecast models.

Then a strong cold front finished things off yesterday with a gusty south wind that quickly switched to northwest in the afternoon. Peak gusts were in the 25-40 mph range for most of us, the 4th time PDX has seen a gust at/higher than 40 mph this season. Lots of moderate wind, but no windstorm in the valleys yet this season. Mental reminder: The HRRR model tends to over-forecast wind gusts, it’s been too high most of the time this season. Our GRAF model has done very well.

Rain is running well ahead of average for November…just over another 1/2″ will send PDX over the typical monthly allotment. But now the weather is slowing down dramatically.


WHAT’S AHEAD?

Much calmer weather which shouldn’t affect your day to day living…

Through at least Thanksgiving Day I don’t see:

  1. A storm of any sort west of the Cascades
  2. Lowland cold and/or snow
  3. A big snowfall to jump start the ski season

In general, upper-level heights will be a bit higher than normal along/off the West Coast. That has not been the case most of the time in the past month. This chart shows 500 millibar height (around 18,000′ overhead) averaged over the next ten days…the lines. Warm colors represent highs higher (warmer) than normal

That leads to less precipitation than normal…both the GFS and ECMWF ensembles are similar (GFS here). Not DRY, but DRIER THAN AVERAGE for this time of year.

Just beyond that time (later Thanksgiving Weekend and beyond) models diverge. At this point GFS ensemble members are bringing in a wet southwesterly flow again, but ECMWF & Canadian models think ridging moves overhead for drier than normal conditions through the end of November. We will see, that’s pretty far out. Regardless, I only see two rainy periods in the next week. That’s later Thursday through Friday, then again Monday (very light). These will be relatively weak systems, not significant wind producers. I love this chart…it shows all 51 ECMWF ensemble members for the next two weeks. Each square represents a forecast 6 hour maximum gust in Portland. The lowest part of the chart shows the average of all 51 members. With just a quick glance I can see where windy periods may show up, plus any real “outliers”. That refers to numbers much higher than others.

Gusty easterly wind tomorrow through Thursday morning shows up well on all ensemble members. Most interesting is that there isn’t a single ensemble member trying for a 50 mph gust in the next 16 days! Of course that doesn’t mean we don’t have a storm coming sometime beyond the next 7 days, but in general we don’t see a stormy period ahead.


SKI AREA OPENINGS

Last week things were looking up with 10-15″ fresh snow on the ground at the ski resorts. We were just a storm or two away from at least a few runs opening up on Mt. Hood. Then 5-6″ rain fell on that snow and warm/humid weather melted all of it! Cold showers last night dropped 2-5″ snow on those resorts. It appears only a dusting is on the ground down at Mt. Bachelor west of Bend. This is not unusual for mid-November as you see, but skiers/snowboarders just remember the big starts. 2017 and last year we had some nice snow on the ground at this point.

What’s ahead?

We sure don’t want to see those higher than normal upper-level heights over the next week as I mentioned earlier in the post. That means weak systems and a bit warmer than normal. So very little accumulation at the resorts at least through next Wednesday.

BUT, things can change quickly this time of year. Stay tuned to see if we get that cooler/wetter pattern as we go through Thanksgiving Weekend.

Chief Meteorologist Mark Nelsen


Pineapple Express Is Here! More Rain Ahead But Mainly Dry Weekend

November 11, 2021

6pm Thursday…

Now THIS is the November weather I remember growing up with west of the Cascades…day after day of rain and mild weather. Some southerly breezes, then a bit of mountain snow. Annoying if you want to get outside, but great to see the ground saturating, reservoirs refilling, and (eventually) a building snowpack in the Cascades. Especially after a brutally hot summer and record dry spring. It’s pouring in past of the metro area right now and we are under a Flood Watch for local areas of flooding through tomorrow. What’s ahead? Read on…

KEY POINTS

  • Showers continue in the metro area and south tonight, while heavy rain continues most of night in a line from Tillamook to Longview and northward.
  • Steadier rain develops later tonight in the metro area and south, continuing through Friday afternoon. The morning commute and midday will be a soaker again!
  • Rain comes to an end all areas west of the Cascades around sunset Friday
  • Saturday should be dry
  • Rain returns north of Portland Sunday, we’ll be right on the edge of that rain line in the city. Definitely dry south and east of here Sunday too.
  • Expect another 2-4″ Coast, Coast Range, and Cascades. 1.00-1.50″ metro, and 2-3″ Longview up to Olympia the next 24 hours

This is what we’ve seen so far; a big dousing central/south Willamette Valley last night, but then heavier rain shifted north of Portland most of today. Of course mountains both east and west of us have been significantly wetter

Notice Portland is one of the driest spots. That’s not unusual. In fact check out the typical yearly rainfall in the Portland/Vancouver area. Charlie Feris retired from BPA many years ago, but continues to maintain a precipitation network of observers. He’s been doing it since about the time I was born!

Precipitable Water chart shows that we are most definitely under an atmospheric river (pineapple express) right now. Let’s just call it an “AR” so I don’t have to type it out each time. Look at that slug of tropical moisture stretching 2,500+ miles from near Hawaii to Washington!

A tool we use to analyze this situation is Integrated Water Vapor Transport (IVT). Basically how much water vapor is being transported in any one location through a cross-section of the atmosphere. Chart below is 4pm today. Numbers show total mass of water vapor passing through each square meter of the AR each second. Got that? Simpler: Bigger numbers equal more moisture moving through any one spot overhead.

You may notice there isn’t much “IVT” going on east of the Cascades. Where did all that water go? It was converted into rain. That “river of water” in the atmosphere slams into the Coast Ranges, then the Cascades. Rising air cools, and moisture must condense into droplets = rain. The heaviest rains fall where high IVT encounters a mountain range perpendicular to the flow. Westerly flow squeezes maximum rain out of these ARs with our north/south oriented mountain ranges. That’s why so much more rain falls west and east of downtown Portland compared to the city itself.

Alright, so the AR is aimed at Washington right now and through much of tonight. By tomorrow morning it has weakened just a bit, but dropping south over Oregon. But don’t worry, there’s still plenty of rain to go around

Then it has fallen apart by Saturday morning, ending the rain over most of Oregon

An even more intense AR sets up Sunday, but this time it’s aimed at Vancouver and NW Washington. We will be right on the edge of that one.

How much rain is ahead? I think the 18z ECMWF shows a good approximation of what we can expect the next 24 hours. Less than 2″ for most areas south of Longview in the lowlands. Up to another 4″ in the wettest parts of the Cascades and Coast Range

We will probably end up with 2″+ in Portland out of this event, pretty good model forecasts so far…

The final part of this AR moves south over us Monday, followed by colder air; snow levels will go below the passes Monday night. But then a relatively dry and cool-ish pattern follows much of next week. The GFS model’s ensemble forecast for Salem high/low temps gives you the general idea.

There’s no sign of a stormy pattern OR low elevation cold/snow in the next 10 days. That can happen once we hit mid-November.

That’s it for now. I’ll be on TV at 8/9pm on FOX12Plus and 10/11pm on FOX12, see you there!

Chief Meteorologist Mark Nelsen


Fall So Far, Plus A Pineapple Express Ahead

November 8, 2021

9pm Monday…

Time is flying, or maybe I’m just getting older. We’re quickly heading toward mid-November so let’s do a quick recap of the season so far.

Meteorological Fall includes September/October/November, so we only have 3 weeks left this season:

  1. Temperatures have been near normal, or slightly below since September 1st. September and November (so far) slightly warmer than normal, but October slightly cooler than average. Nothing interesting here
  2. Wet! After an incredibly dry spring/summer, rainy weather arrived in mid-September. We are very fortunate it didn’t wait a few more weeks. It’s always amazing how we go from desiccated/dry ground and brown vegetation to green within just a few weeks each fall. Since that time, 8.87″ rain has fallen in Portland! As always, the mountains scoop up lots more rain. Mt. Hood Test Site at the bottom of Timberline’s Pucci Lift has seen 15.30″. North Fork SNOTEL south of Multnomah Falls at 4,000′ picked up 27.70″. A SNOTEL station named “Sheep Canyon” is on the southwestern slopes of Mt. St. Helens. In that notoriously wet location, over 3 FEET of rain has fallen since the wet season began; 37.40″. It’s hard to believe, but those numbers are about normal for this point in the fall. The Cascades are very wet (or white) late September through springtime!

Here are some other numbers showing just the last 30 days. Screaming message here is that you shouldn’t complain about rain in the I-5 corridor…tons more rain regularly falls west and east in hills/mountains surrounding the lowlands.

SUMMARY: THIS FALL HAS BEEN QUITE “NORMAL” SO FAR

November is here and it’s one of the 3 wettest months of the year west of the Cascades. November, December, & January are close to the same rain-wise. It’s also the month that we slowly slip into our “winter” conditions west of the mountains. High temperatures drop down through the 50s.

WHAT’S AHEAD?

More wet weather. Sure, today was amazing with early blue sky and comfortable temps in the 50s. But a relatively weak system is sweeping north along the coastline; we’ve got a wet night ahead. The Cascades picked up 4-12″ snow over the weekend, and I expect another 4-6″ through tomorrow above 3,000′. But don’t get excited about an early start to the ski season yet…

PINEAPPLE EXPRESS

Starting Wednesday, upper-level ridging pushes warmer air north along the West Coast. That ridge LOOKS strong enough to give us warm & dry weather Thursday based on this map

But plenty of warm & subtropical air will be flowing northeast from north of Hawaii. Check out “Precipitable Water” on Thursday. You can see why these narrow ribbons of warm/moist air are named “Atmospheric Rivers”.

When it’s a warm one like this, freezing levels soaring over 9,000′, we also call it a “Pineapple Express”. Same idea, a warm, cloudy, and very wet weather pattern for us.

Since this is like a narrow firehose of rain that flips around easily, forecast rainfall can be all over the place as well. The ECMWF forecast through Friday morning seems a bit excessive showing 2-4″ in the western valleys of Oregon and SW Washington just through that time.

It’s better to use “model ensembles” in a situation like this. For Salem, the 51 members of the ECMWF model show an average of 2.50″. That’s the bottom half of the chart. Each of the horizontal lines on the top half show accumulating rainfall the next 6 days (at Salem)

For this reason (and at this moment), the event late Wednesday through Friday does not appear to be a significant flood producer. But, always something to watch as we get closer.

Snow levels will be very high Wednesday night through Sunday, mainly above 8,000′.

Add 3-6″ of rain to a fresh foot of snow later this week and and you can guess what will happen. There won’t be much left. But hopefully a bit colder next week and MAYBE some ski terrain opening up for the weekend before Thanksgiving…we will see!

To sum things up…it’s going to be very wet this week, especially Wednesday night through Friday. But models are also implying the ridging pushes most or all of the rain north of us next weekend. I’m skeptical…more later in the week

Chief Meteorologist Mark Nelsen


Winter 2021-22 Thoughts

October 27, 2021

October 27th, 2021

About this time each fall people start asking me “What this winter will be like?” or “I’ve heard it’s going to be a bad winter!“.  Actually sometimes they start asking in August!  For the record, 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”.  That’s because 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 ideas by looking over some weather tidbits.  I’ve been doing this for quite a few years and it seems to work.

For those of you with a short attention span, just three points:

  1. Plan on an “active” winter this year.  The last 3 winters were quite “boring” (most of the time) for the weather professionals. Which means they were “easy winters” for regular folks (most of the time). Of course we all remember the 4 day stretch of snow/ice around Valentine’s Day right? But most of last winter was quiet weather-wise except for that event plus some flooding in mid January. The odds are tilted toward more changeable weather this winter; I expect it to be busier here at KPTV. A better chance for a windstorm, flooding, and lowland snow.  And I doubt we’ll be locked into weather patterns for weeks/months at a time.
  2. Expect at least once we’ll see some snow or freezing rain in the metro area and lowlands west of the Cascades.  I would be surprised if we get through this entire winter without measurable snow in Portland. I’d peg the chance of “sleddable” snow at about 70% some point between November 10th and March 1st. No, we have no idea when that could happen until at least 7-10 days ahead of time 
  3. Expect a good snow year in the Cascades. Good for both water next summer and skiing during the winter.  Go ahead and plan on a normal ski season with the usual variable ski conditions from week to week. I’d give this about a 70% chance of happening too. It IS possible to get a low snow year during a La Nina winter. In fact two La Ninas back in time we saw terrible ski conditions through January! Then February/March were incredible.

SUMMARY OF THE LAST 2 WINTERS

Two winters back…2019-2020  So boring…this was our 2nd consecutive “El Nino” winter. There was a real lack of Pacific storms; it was as if the jet stream just didn’t want to perform last winter.

Last winter…2020-2021 It was a surprising La Nina winter because of the mild temperatures, plus almost nothing interesting happened weather-wise until mid January! Some widespread (light-moderate) flooding showed up at that time, but then all was quiet until a 4 day blast of cold air arrived starting February 11th. That cold air was overrun by plenty of Pacific moisture which produced a snowstorm from Portland north/east and a severe ice storm from south metro down to around Albany in the Willamette Valley. Then temperatures warmed and typical (wet) winter weather resumed. We dried out dramatically in March and April, but with plenty of cool temps.

You can check out the rest of my winter recap presentation here: https://oregonams.files.wordpress.com/2021/10/mark-nelsen-winter-weather-recap-2020-2021.pdf

So much of the past 3 winter seasons have involved a lack of storminess and drier than average weather. About time for some action don’t you think? But that’s what I thought would happen this past winter too…there’s so much we still don’t know about our climate.


WHAT’S AHEAD FOR THIS WINTER?

We have entered weak/moderate “La Nina conditions” once again this fall. Models tell us most likely it’ll be a weak to moderate event through the winter. So this will be our 2nd La Nina winter.  That can give us a few hints, definitely not a forecast, but what direction our winter might be “weighted” toward.  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/moderate event.   Right now the Oceanic Nino Index (or ONI) is in the WEAK La Nina category.  

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. Anything below the “-0.5” is weak La Nina, below “-1.0” is a moderate event. Strong would be “-1.5” or lower.

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 based on a moderate La Nina event:

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. And the chance for “wet” is much higher in northern Oregon than the southern half of the state. Although the current weather pattern this week suggests otherwise with an incredibly wet northern California very early in the season.

1a.  Flooding

This goes with the rainfall.  For obvious reasons we tend to have more flooding events in La Nina winters due to the wetter weather. Keep in mind we haven’t seen a major regional flood in 24 years. That was 1996. Previous big flood was 1964. I wouldn’t say we are “overdue”, but one of these winters it’s going to happen again.

2.  Mountain Snow

Lots of precipitation and cool weather systems = plenty of mountain snow.  This is probably the #2 most likely event.  7 out of the last 10 La Nina winters have brought above normal snow to ALL elevations in the Cascades.  Note that there CAN be a bad year; it just happened during winter 2017-18. Ouch! Check out the mid January snowpack during 2001 & 2018…

3.  Foothill Snow

This happens in some 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.  It didn’t happen last winter, but colder than normal ocean water is poised to the west/northwest of the PACNW.

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 26 years ago!  14 years before that we had the major November 1981 storm.  It’s interesting that all the 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

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.  Three La Ninas in the last 20 years have produced a major snowfall here in Portland…December 2008, January 2017, & February 2021.  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.

ADDITIONAL THOUGHTS:

The elephant in the living room I suppose is the fact that our winters are gradually warming, and snow in Portland is more rare than it used to be when we look back more than 70+ years. Although the past couple of decades total winter snowfall seems to have stopped it’s downward plunge.  Take a look at total snow each decade since the airport observations started about 1940. Divide by 10 to get average per winter.

And downtown records that go back to the late 1800s.  The low spot in the 80s is missing some data…it should be a bit 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 a good snowstorm. We all remember that event and that pops up the long-term average.  It is interesting that the last 3 decades seem to have leveled out a bit at around 4″ per winter at both downtown and PDX locations.

WHAT ELSE COULD HAVE AN EFFECT ON OUR WINTER WEATHER?

  1. Cooler Water In Eastern Pacific There is no blob of warm water in the northeast Pacific like last fall/winter. In fact much cooler than normal now.

2. Pacific Decadal Oscillation (PDO) This is directly related to the sea surface temps. Typically during a La Nina we get a negative or “cool phase” of the PDO at the same time. Last year that was not the case. But this year we seem to be in the cool phase (right side figure below). Could that make this La Nina winter behave significantly different (cooler/wetter) compared to last year? You can read up on the PDO here: https://www.climate.gov/news-features/blogs/enso/going-out-ice-cream-first-date-pacific-decadal-oscillation

This gives the general picture

3. Anthropogenic Global Warming (Climate Change) A warming globe doesn’t necessarily mean we don’t get cold air outbreaks or snow. It can also mean the usual circulations get disrupted. For example it seems to me we just aren’t getting as much storminess over the eastern Pacific the last 3-4 years. That’s just anecdotal of course. But has something shifted the past 20 years? We don’t know, although 30 years from now, we might look back and notice something did change during this period. There is still a LOT we don’t know about climate.

That wraps it up…as always we’ll see how the winter turns out…my money (again) is on “wet”, “good Cascade snow”, and at least one “snow/ice event” in the lowlands. Maybe several, but hopefully I won’t be spending too much time at the hotel right near the TV station…

WHAT OTHERS THINK

Each autumn the Oregon chapter of the American Meteorological Society puts on a “Winter Weather Conference”. It’s my favorite meeting of the year! I have been a part of this chapter my entire career. Speakers present their thoughts/outlook/forecast for the upcoming winter. The public is always invited. Last year and just this past week we gathered virtually due to the pandemic. Interested in watching? Check out my recap, plus 5 different outlooks on our Oregon AMS web page. I was especially impressed by the passion/talent the younger folks are bringing to our chapter! There is some really good information in each of these presentations. Enjoy!

Chief Meteorologist Mark Nelsen