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  • Posted

It was another fantastic spring day across the region wasn’t it? Just a few thin high clouds drifting lazily by at times. We made it to 68 in Portland, just a few notches down from the 71 yesterday (March 31st). Salem and Eugene were a bit warmer than yesterday.

March Recap

In my opinion, we’ve had a great start to spring if you like to get outdoors. March was drier than average, with plenty of partly cloudy or sunny days. It was our 7th driest on record at PDX (out of 81), and the 2nd driest during a La Niña winter/spring.

Just as interesting? We’ve now gone through four consecutive years with drier than normal conditions in March. Payback will be a real tough in some future March!

And you can see most of the West has been quite dry this past month

What about temperatures? A bit cooler than average. Not a huge departure, but most of Oregon has been cooler than normal.

Is this unusual? Not really. Looking back at past La Nina springs, there is a very strong signal for cooler than normal across the Pacific Northwest. This is a composite of April-June temperatures for the last 20 La Nina springs. Pretty clear signal isn’t it?

One would think a cool spring would also be wet, but that’s not the case. April through June precipitation from those same 20 springs…well below average.

I don’t mind these springs too much; plenty of sunny or partly cloudy days mixed in with the wet days. Plenty of chilly nights and late frosts (like this year), but a cold/clear night is followed by very strong April/May sunshine too!

Snowpack is still running well ahead of average in northern Oregon; no significant spring melt yet due to the cooler temps. Southern Oregon is not in good shape as of April 1st. Lots of drought issues are likely across the Klamath and Good Lake basins

What’s Ahead?

April is what I call the “greening up” month west of the Cascades. Most deciduous shrubs and trees come alive this month; bare of foliage to start, then flush with fresh leaves & green by April 30th. It’s very dramatic in the woods around my home. Right now the ground is pretty much bare and bright sunshine makes it down to the forest floor. But four weeks from now all the ferns will have popped out of the ground, alder/maple trees will be leafed out. It turns darker and shady in the woods from that point through October.

Portland’s average high temperature rises from 59 > 64, and we typically see 5 days at/above 70 degrees. Last year we made it to 76 degrees late in the month

We have also entered the drier half of the year…just barely. April is slightly drier than October in a typical year as the rainy season slowly winds down

In the short term, we’ve got a dying cold front that brings a few sprinkles to the northern Oregon coastline tomorrow. Then (unfortunately) on Easter a splitting upper-level trough brings another dying front overhead. Lots of clouds that day but not much rain! The fresh 00z GRAF model shows how little rain we expect through Sunday afternoon. If there is no color on this map, that means less than 0.10″ precipitation.

The result? Not much rain and temperatures near normal for this first week of April. And…

EASTER WILL NOT BE A WASHOUT, JUST LOTS OF CLOUDS PLUS A FEW SPRINKLES OR A SHOWER

Chief Meteorologist Mark Nelsen

  • Posted

9:30pm Sunday...

Here we are in mid-January, halfway through meteorological winter (December-February). We've had ONE significant weather event during that time west of the Cascades; the wind and rain storm earlier last week. It has been a very mild winter as well. By the way, I just confirmed the peak gust at PDX was 50 mph during the last minute of January 12th (11:59pm).

December 1st through January 16th has been the WARMEST 1ST HALF OF WINTER ON RECORD IN PORTLAND! You like that big red font? This comes with one big caveat. Portland has grown tremendously and we have an "urban heat island" now. It's most noticeable at night. A lot more people live here compared to 60 years ago. That means even if the climate was not warming (it is), we would be seeing Portland's average temperature rising due to that effect alone. But check out Redmond (little/no urban influence there). It's the warmest since 1951! And Olympia has seen the 3rd warmest after 1951 & 1981. Going back 100 years, Salem has seen its 5th warmest first half of winter. My point is that yes, it has been a very mild winter...so far.

Snowpack is well below normal, running about 60-80% of average in the Cascades. Yet 2018, 2012, & 2011 La Nina years saw similar or lower snowpack at this point around Government Camp. Many of these years we play "catch-up" with snowpack in February/March. We'll see.

Of course weatherwise it's been a very slow winter (again) for forecasters but we think that will be changing as we head into a colder weather pattern. And yes, we may be flirting with low-elevation snow at some point in the next 10 days.

Quick Summary

  1. The next 7 days will be much drier than average, it's possible we don't seen any rain until NEXT Sunday
  2. There's no sign of an "arctic blast pipe-buster" for at least the next 10 days. That is a big shot of cold air from Canada; think lows in teens or lower and highs around 30 or below. I don't see that happening.
  3. Beginning next Sunday, expect a cold & wet weather pattern with heavy Cascade snowfall
  4. Beginning next Sunday, we may see our first widespread foothill and Coast Range snow plus there may be more beyond that. This winter, sticking snow below 2,000' has been rare. That will change for the final week of January. If you live between 1,000' and 2,000', you can expect to see snow more regularly beginning next Sunday.
  5. AT THIS POINT, we do not have (sticking) snow in our forecast (for lowlands) through at least next Sunday. That's because we don't see a setup that would drag sticking snow all the way down to the valley floor, or sea level. But it may be close to sea level at some point in the 7-10 day range. Keep a close eye on that Sunday-Tuesday forecast NEXT week.

What's Changing?

We have a strong upper-level ridge right over us and it's staying put through Wednesday. This is the flow of air up around 18,000' (500mb). I've annotated the ridge with a yellow line. This is Tuesday

By Thursday, a cold upper-level trough is dropping down the back side of the ridge as it backs off to the west.

But it appears just about all moisture will remain offshore, so we're going with just a few light showers (rain) Thursday evening. Weather geeks will remember that THIS was going to be the big system that would drop south and bring in arctic air at the end of the week. That was on some models maybe 5-7 days ago. Now it's just a weak ripple in the northwesterly flow. Then by Monday the 25th, a much deeper & colder trough is moving into the Pacific Northwest

This one is preceded by a stronger cold front and plenty of moisture next Sunday. Depending on the exact track of surface low pressure, this setup CAN bring snow to sea level. I've got two thoughts on that. First, neither the GFS or ECMWF models at this moment retain enough cold offshore flow to bring widespread sticking snow to the valley floor. That's because the low is coming in from the northwest. Second, the air isn't that cold to begin with and we're quickly going to onshore (mild) flow. That's almost always a snow killer. That system next Sunday reminds me of several during the 2007-2008 winter that brought abundant snow to Detroit, the Gorge, Coast Range, and the Cascade foothills. But not quite cold enough for lowest elevations to get in on the snow action. 850mb temperatures are forecast to be around -5 to -6...again, not quite cold enough for a big snow event in the metro area next Sunday. I think the ECMWF rain/snow forecast shows the situation well for Sunday night

Beyond that, the upper-ridging wants to move even farther west of us, allowing a cold trough to set up over the Gulf of Alaska and send cold waves of moisture our way. A quick animation of those upper-level heights from next Monday the 25th to Monday February 1st (a full week), shows the progression westward, along with the coldest air

The final image tells me a lot.

It says that beyond about day 10, we're into a classic La Nina pattern that's wet and cool. Tons of mountain snow, but not much chance for it in the lowlands. This will likely be the first big week of mountain snow this winter, maybe like the middle of last January?

Check out the GFS ensemble forecasts for snow. About 1/3 to 1/2 produce "sleddable" snow in Portland sometime in the next 2 weeks. I think that might be generous considering what I'm seeing right now.

You can see model forecasts of high temperature (usually a few degrees low) dip to a minimum early NEXT week and then rise again as we get more systems off the mild Pacific. This is the GFS.

One more thing that gives me confidence that we're not headed into a major cold/snowy spell...the 850mb ensemble charts. Excellent agreement through the next 7-9 days, then a rise (warming). Almost no members below -7 through the next two weeks. This is just the ECMWF, but GFS is similar.

This wasn't the case 5-7 days ago. As we get closer to a change, models come together most of the time and this is a good example.

That's it for now. Of course even without a "major cold/snowy spell", we can get an event where part of the lowlands get snow and that may not show up until just a few days ahead of time. I'll be working regular shifts for the next 3-4 weeks as we wrap up this "winter". We should still be having some fun even if no widespread snowstorm shows up in the valleys.

Make sure you follow me on Facebook @marknelsenweather, Twitter: @marknelsenKPTV, I update those far more often than this blog. And don't forget our podcasts here: https://www.kptv.com/podcasts/weather/

Chief Meteorologist Mark Nelsen

  • Posted

9:45pm Sunday...

Let's do a quick checkup on January so far:

1. It has been VERY WARM compared to what we usually see in early January. Through the 10th, Portland is running 6 degrees above average, 7 at Redmond, and 9 degrees at Pendleton! Almost the entire USA has been much warmer than normal...who stole Winter 2020-21?

2. It has been WETTER than average across much of the PACNW, more so the farther north and west you go

What's ahead?

  • Mild to warm conditions continue for the next 8-10 days
  • We get soaked Monday-Wednesday this week, then much drier Wednesday through the 18th-20th
  • There's no sign of lowland cold/snow/ice west of the Cascades through at least the 20th

The Stormy Weather

I see an "atmospheric river" headed our way tomorrow through Wednesday. That's basically a low level flow of very moist air that hits the Coast and Cascade ranges, squeezing out a lot of precipitation. Of course plenty falls along the beaches and in the valleys too, but not as much. This will be powered by the Pacific jet stream reaching from Japan all the way to the PACNW. Check out the 235 mph maximum wind over the far western Pacific Monday afternoon!

A good way to look at heavy rain events/atmospheric rivers is by using Integrated Vapor Transport (IVT); kind of like checking a river gauge to see how much water is flowing through. That's quite a "river" tomorrow evening...

Then again Tuesday night, this is around 10pm.

Since the flow is not coming directly west-east, it's possible we get a bit more rain into the valleys than we sometimes see. ECMWF and RPM are both pretty reasonable showing maybe 2" in the valleys by the time it dries out Wednesday

I think 3-6" is a good bet in the mountains around us; this is similar to what we saw this last time around. That led to minor flooding on some coastal rivers, but nothing significant inland. That said, anytime we get this much rain in just a couple days it's fair to expect some mudslides and/or landslides in spots.

Wind is something else to watch. The boundary line between cooler air to the north and warm south of us will be sliding north/south through the region a couple times. When it is just to our north, we'll get a gusty southerly wind, especially if a "wave" moves along the front. That should happen tomorrow night and again late Tuesday night. There is some model disagreement on how strong the wind gets based on their disagreement where the waves, or even a surface low track. Right now the ECMWF seems reasonable showing the stronger 2nd "event" late Tuesday night.

Gusts 60-70 on the beaches and 35-50 in the valleys; not a big windstorm by any means.

As of now the NWS does not have a flood watch OR any wind advisories/watches/warnings. I assume that will change in the next 12-24 hours.

To Summarize

  1. Expect light rain Monday, but it'll turn heavy at times Monday night through early Tuesday. Then a 2nd wave of rain later Tuesday through around sunrise Wednesday. 1.50-2.50" in valleys and 3-6" in mountains. THIS SHOULD BE ENOUGH FOR LOCALIZED PONDING OF WATER OR FLOODING, BUT NOT ENOUGH FOR A WIDESPREAD FLOOD EVENT.
  2. Expect one surge of southerly wind about this time tomorrow evening or a bit beyond, calm wind Tuesday, then a stronger surge sometime Tuesday night. NEITHER APPEARS TO BE A SIGNIFICANT WINDSTORM, but I'll be keeping a close eye on it of course.

In the Cascades

As mentioned in a previous post, and in our podcast, Cascade snowpack is running below average for early-mid January. Things will get a bit worse over the next week. Check out the snow level forecast

Not good. Only Wednesday and late Friday/Saturday are reasonably cool. ALMOST ALL OF MONDAY-TUESDAY'S PRECIPITATION WILL FALL AS RAIN AT THE SKI RESORTS. If you want to ski, go VERY early Monday, or wait until Wednesday-Friday. Our 7 Day forecast for the Mt. Hood area...

Long Range

I'm about out of time so I'll make it brief. There are pretty clear signals on all models that some sort of significant pattern change may arrive in the January 20th-24th timeframe. The warm ridging that is giving us mild weather, along with an atmospheric river moving through that ridge, is shifting much farther west in about 10 days. Next Sunday you can see a strong ridge right over us = mainly or all dry MLK Weekend

And here's an example of one week later, quite a change with heights much lower over us = cooler.

Will this finally give snow to elevations down around 2,000' and below like a normal La Niña winter? It's been mostly absent so far! All models at least show cooler systems coming in from the northwest at that time, and a few ensembles bring arctic air down from the north. It's far too early to know what we're going to get out of this. It could be 1) A more typical La Niña pattern with cooler systems but still no valley snow, or 2) Colder arctic air slides south and really cools us off, with the chance of lowland snow. Nobody knows as of now. I'll post again later this week or for sure next Sunday with an update.

Chief Meteorologist Mark Nelsen

  • Posted

It's a brand new year; we're 4 days into January 2021. What has changed over the past week? Not much; it's still mild and wet. We ended up with near average December rainfall in Portland. For the region as a whole it's been a very wet start this month. Astoria around 5" in just four days!

And 1.50-3.00" in the metro area

Not enough for flooding, but the ground is saturated. Precipitation the past month looks like a classic La Nina winter setup; a wetter than average northwestern USA, but very dry Southwest

Snowpack is running a bit below average over and west of the Cascades.

That's not due to lack of precipitation, but "warm storms". Or at least warmer than average. An example would be this past weekend. Just a few inches fell at Government Camp and snow depth hasn't changed. But 2 feet of snow fell up at Timberline Lodge (6,000') which stayed above the snow level most of the weekend. This is more of a typical wintertime El Nino setup...plenty of precipitation but mild storms. The last time I remember such a mild La Nina year was 2000-2001. At least in 2017-18 we had cold arctic air move south into the USA and give us a cold/icy/snowy Christmas. You see that trend continuing this first week of January. See forecast snow levels, based on 850mb temps off the ECMWF model

Some snow is again falling down to the passes right now, but a warmer system arrives Tuesday night and Wednesday morning. We do get a nice cold system Friday; should be a good snow producer for lower elevations in the mountains. You see another snow level spike the middle of the upcoming weekend. Although for now most of the precipitation with that system is forecast to fall in the cooler airmass with/behind the cold front.

What's ahead? More of the same for at least the next 10-15 days. Notice the ECMWF ensemble forecast high temps keep our highs near/above average. Ignore the last day, it stops in the early morning (when it's colder)

Almost constant westerly flow off the Pacific ocean is the culprit, in fact upper-level heights RISE a bit next week leading to even warmer temps! A break from the rain? No more than a day here and there; hardly any gaps on those same 15 day ensembles

You probably already know what that means for a lowland snow chance...essentially near zero through the first half of January, possibly all the way to around the 20th. It's somewhat startling to see not one ensemble member giving Portland significant (or any) snow in the middle of a La Nina winter.

The ECMWF ensemble 850mb temperature forecast shows almost no members below -6/-7, what we need to see to at least get snow down into the West Hills.

As for rain, intensity will probably back off in the next 10 days as upper-level heights rise. Notice a 3-4" forecast for Salem, that's just typical wet, nothing too heavy.

To wrap it up, the message remains the same as we head into the 2nd half of winter...mild and wet through the foreseeable future.

  • Posted

9pm Sunday...

It's been 9 days since I last posted. Part of the reason (other than keeping busy at work) is the lack of stormy weather. As mentioned in the previous post this first half of December was looking drier than average. Sure enough...the 14 day anomaly across the western USA shows a very dry month SO FAR...

Temperatures have been running near average over the Pacific Northwest. Although wintertime inversions in some valleys/basins have given cooler than average (Pendleton, Tri-Cities)

Again, nothing too exciting. We had a pretty good easterly wind episode the first week of the month; Troutdale saw 7 consecutive days with gusts 35 mph or higher. That said, it is December and that sure isn't unusual. We've seen snow in the central/eastern Gorge twice now, although real marginal both times... the 2nd was last night. I had a wonderful day of light rain showers with the temperature between 33-36 degrees all day long (at home). Snowpack IS running near average in the Cascades which is great news. As I write this I see Hwy 26 through Government Camp has turned snowy again

A couple of notes...nowadays I spend time putting out shorter thoughts/maps etc... on Facebook, Twitter. It's much easier on a busy night to quickly post a model chart or other weather information there as opposed to a long blog posting. You can find me on Facebook as @marknelsenweather or Twitter as @MarkNelsenKPTV Also, we have a Northwest Weather Podcast.

Lots of fun! Just this past week the four of us (Brian MacMillan, Jeff Forgeron, Anne Campolongo, & I) discussed La Niña so far, Vista House wind, Solar Eclipses, & holiday plans for the weather center. Several weather folks having a jovial conversation...what could be better? You can find it here: https://www.kptv.com/podcasts/weather/

What's Ahead?

1- We are turning wetter now and should see more regular rainfall over the next 10-14 days. I don't see a significant dry spell (2+ days) between now and at least the middle of next week.

2- There's NO sign of real cold weather or lowland snow west of the Cascades for the next 10+ days. That bumps us up right against Christmas of course. My gut feeling is that we won't be seeing snow anywhere near the lowlands for Christmas Week (next Sunday through Christmas Day).

3- I don't see flooding or an especially stormy pattern for the next 7 days. Most of the weather systems moving inland are relatively week; I'm not seeing big deep low pressure areas in the eastern Pacific. Of course that could change, but not this week.

I can explain both #1 and #2 just by showing you the 500 millibar forecast from the GEFS (GFS ensembles) for the next two weeks.  Red is above average heights, blue is below

It's a continuing train of weather systems moving west to east in a "zonal" flow. That's as opposed to a "meridional" flow which would lead to more north-south movement. Also notice there are no prolonged ridging episodes (dry weather). In this pattern it never gets cold because the chilly arctic air is bottled up to the north of the jet. You aren't going to get lowland snow in this setup. Look at the 850mb ensemble chart from the ECMWF model.

I'm amazed that through the entire 2nd half of December there are almost no members (each line is one of 51 ensemble members) that drop below -7. That's about what we need for lowland snow in onshore flow. Very consistent westerly flow = mild.

Confirmation comes from the ECMWF ensemble forecast of Portland snowfall the next two weeks (through Sunday the 28th). Not a single member tries for 2" or more snow.

There are hints that Christmas Week might be a bit drier than this week and coming weekend. You see quite a few more gaps in 24 hour precipitation totals during the 2nd week.

What About La Niña? Shouldn't Weather Be Wilder at This Point?

No, not necessarily. Remember that La Nina doesn't guarantee lowland snow, and it sure doesn't guarantee lowland snow and stormy weather between November 1st and January 1st. For all we know we've got crazy wild weather action coming in January or February! For fun I looked back through the last 8 La Nina winters to see what happened. Some start just like this...mild and dry-ish. My brief notes on each.

2017- A boring November, dry ridging 1st half of December. No decent skiing until Christmas Vacation

2016- Crazy and wild ride. At this point we had just gone through an ice storm and were preparing for a 2pm arrival (December 14th) of a snow storm. Everyone hit the road at the same time and you remember what happened. I always remember the date 12-14-16.

2011- Stormy November, Dry December. Then a big atmospheric river wipes out quite a bit of snow on Mt. Hood right after Christmas. January 2012 following was stormy

2010- Stormy November, arctic air at Thanksgiving

2008- Boring November, dry December start. Arctic blast arrives right about now (Dec. 14th). Two weeks of snowy mayhem followed...

2007- Boring/dry/mild November, huge coastal storm and widespread flooding just north/west of metro early December. A series of colder storms began in mid December bringing feet of snow to the foothills and many feet the rest of winter to the Cascades

2000- Nothing all that interesting, cold/dry November, in fact entire winter was dry-ish. Didn't fit La Nina pattern at all

1999- Warm & wet November

1998- Very wet November and December, arctic blast around December 17th

1995- Warm and wet November, stormy December included the last major regional windstorm (12-12-95)

You can see this current year isn't a very good fit for any the last 10 La Nina winters. Maybe similar to the last one 2017-2018? Interesting...

That's it for now, enjoy the rainy weather. Best chance for some dry is tomorrow and maybe sometime between Thursday showers and renewed rain on Saturday...possibly Friday.

Chief Meteorologist Mark Nelsen

  • Posted

10pm Sunday…

Well, that’s been an exciting 5 days since the election started eh? Since I love numbers and politics I’ve watched everything closely. Now that things are settling down I figure we should talk about weather. And what a change we’ve seen!

For the first time this season we’ve seen sticking snow down below 3,000′. I took a run today, midday, with a temp in the upper 30s. It felt like December under a gray sky (east side of metro). Portland saw it’s coldest day of the fall, just 47 degrees

You know winter is close when at 8pm we’ve already got parts of the metro area below freezing.

Expect widespread mid-upper 20s tonight for another hard freeze. Whatever survived frosts a couple weeks ago probably won’t make it through tonight. We’ve seen a few inches of snow at Government Camp, maybe 4-5″ higher up at the ski resorts. Here’s the 8:45pm view from the top of Upper Bowl at SkiBowl

The rainy season has arrived; that’s the screaming message on maps/models this evening. In fact if you’re looking for a 3 day period of dry weather? Extremely unlikely…

Summary of What’s Ahead

  1. Expect steady rain or showers just about every day for at least the next week to 10 days west of the Cascades. IF we somehow squeeze in a mostly dry day, consider that a bonus! Somewhere between 2-4″ rain could fall in the next 10 days…
  2. Temperatures will remain between 40-50 degrees most of the next week too. A mild Pacific airmass will be in control of our weather most of that time.
  3. I don’t see a setup for low elevation snow OR ice/snow in the Gorge for at least a week, probably much longer. There’s no sign of cold Canadian air surging south in the next 7-10 days either
  4. Snowpack will be building in the Cascades over the next week. IF we don’t get a set of warmer systems NEXT week, I could see ski areas trying to open up at least a few runs!

Details

As expected we’ve seen a surge of cool/dry air drop south into the Pacific Northwest, thus the cold temps tonight. But starting tomorrow afternoon our weather will be dominated by a succession of cool-ish weather systems coming in off the Pacific. For at least the next week, none of these are forecast to be “warm” or related to atmospheric rivers. For example check out the ECMWF 850mb ensemble chart. Each thin line represents one of the 51 ensemble members. That’s for the next two weeks. It’s temperature (C) at around 4,000′. So the “zero” line means freezing around Government Camp.

Notice there is general agreement that there won’t be any extra-warm ridging or cold spells. In fact there’s only one or two of those members showing anything really “cold”, at the end of the run. Otherwise it’s generally just a little below average (green line) for this time of year; excellent for mountain snowpack.

Then check out precipitation from the GFS ensembles. Tomorrow through a couple of days before Thanksgiving (2 weeks out). Wet!

It shows six hourly rain totals for each of the 31 ensemble members. Each horizontal line (upper part of chart) is one member. You don’t see many gaps do you? This says it’ll be hard to find much dry weather the next two weeks. Other models are similar. The reason? A typical November Pacific jet stream aimed at the West Coast. Six days out, this coming Saturday

Models are telling us somewhere between 2-4″ rain could fall in the next 10 days west of the Cascades. Very wet, but…it IS November. And precipitation in Cascades maybe around 8-12″. Get ready for an overdue soaking, it’s time.

Snow levels linger between 3-5,000′ over the next week.

Snow at 4,000′ will come and go, but it’ll be ALL snow up above 5,000′. The ECMWF model shown here would imply 2-3 feet may fall at the top of Skibowl, and the upper parts of Mt. Hood Meadows and Timberline ski areas too. Ignore the Gorge, that’s a contouring issue with the terrain.

This COULD be enough to jump-start the ski season a bit early! What we don’t want to see this early is a warm/wet storm following next week to melt the snow. That’s not unusual in November. Last year there was some very basic skiing for Thanksgiving, but then things lagged until we got to mid-January. But this upcoming pattern looks great!

Again, there’s absolutely no sign of lower elevation snow. This is a mild westerly-flow setup, just a bit cooler than normal. Take a look at the stable temperature regime from the ECMWF, actually that’s weirdly stable.

Maybe this will be a 2007-2008 type La Nina winter? That’s when it hardly snowed in Portland, but multiple systems came down in WNW flow pummeling the Cascades AND the foothills with feet of snow. We will see. It’s still very early…kind of like looking at those first few hours of election results and making an assumption of how things were going to play out.

So remember, you’ve got a mainly dry day tomorrow to get outdoor projects done (I have a few), and then it’s on to wet, wet, wet…

  • Posted

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.  Since it’s 2020, I suppose this year everyone gets a pass.

I don’t put out a “winter forecast”.  That’s because the few forecasts I see are often (not always!) 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 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 two winters were quite “boring” for the weather professionals. Which means they were “easy winters” for regular folks. I think we’ll see more changeable weather this winter; I expect to be quite a bit busier here at KPTV. A better chance for windstorms, flooding, and lowland snow.  And I doubt we’ll be locked into weather patterns for weeks/months at a time as we’ve seen the past two winters.
  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. Any forecaster that claims so is making it up or click-baiting you…#FakeWeather.  
  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 the last one gave us terrible ski conditions through January! Then February/March were incredible.

SUMMARY OF THE LAST 2 WINTERS

Two winters back…2018-2019  Up until around February 3rd 2019, we had experienced the most boring winter I can remember in my 28 winters forecasting in the metro area.  Long periods of weak weather systems, almost no real “storms”, and mild temperatures.  This was typical for a weak “El Nino” winter.  That means the tropical Pacific Ocean was a bit warmer than average.  Things were progressing according to plan…but then all hell broke loose around February 5th.  Cold northerly flow became a common weather theme for much of the following five weeks!  Several snowstorms moved through the region, affecting different parts of the FOX12 viewing area at different times.  Who can forget the “Kale Fiasco” when some metro-area stores ran out of kale & other groceries?  A good learning time for local forecasters…

Last winter…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.

So much of the past two winter seasons have involved a lack of storminess and drier than average weather. About time for some action don’t you think?

 

WHAT’S AHEAD FOR THIS WINTER?

It appears we have a weak to moderate “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.  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 on the edge of WEAK to MODERATE 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”.

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.

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 the last La Nina in 2017-18. Ouch! Check out the mid January snowpack during the last event…

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.

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 25 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

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.  Two La Ninas in the last 20 years have produced a major snowfall here in Portland…December 2008 and January 2017.  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 50+ years.  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 1 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. Warm Blob In Eastern Pacific The sea surface is much warmer than normal in the eastern Pacific once again this fall. Some would consider it another “warm blob” offshore. I can’t find a La Nina in the past 40 years that started with such a warm ocean offshore in October. Local meteorologist Charlie Phillips has a great writeup about this in his blog: http://charlie.weathertogether.net/2020/10/18/blob-the-third/

It’s possible the relatively shallow layer of warm water gets “mixed out” as fall/winter storms arrive, we will see.

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. That is not the case this time, or at least ocean temperature anomaly doesn’t seem to match the current “cool phase”. Strange, although sometimes it happens. 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 2-3 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…

Chief Meteorologist Mark Nelsen

  • Posted

Weather is a bit slow this evening...

We've seen some weather action the past few days with three Pacific frontal systems moving across the region. That first one Friday night and Saturday morning was sure a soaker; up to an inch in parts of the metro area. Our October rain total is slowly starting to add up

Western slopes of the Cascades have picked up 7-9" of rain the past month...that has pretty much finished off the fires up there!

Last October was very dry, but we're tracking a bit wetter this year so far

After a very warm start (and warm September!), we've cooled back to normal

What's ahead? Typical October weather...lots of clouds and some showers at times.

A large upper-level ridge is building just west of us. It'll be the main factor in our weather over the next week. It looks about like this right now

By Friday...

The forecast is very tricky Saturday through the middle of next week. That's due to the ridge wanting to move just slightly farther west and "flatten" a bit. That leaves the door open to weak systems moving by to the north. Basically we may get clipped by several waves of clouds and light rain showers. You can see one moving by Sunday

The morning ECMWF model (pictured here) really flattened the ridge and carved out a cool upper-level trough. This would be a setup to bring light snow down below 5,000' in the Cascades. But other models and even some ensemble members of this model keep a stronger ridge closer to us. We'll see. I think the main point is that we're probably not headed into a warm and sunny 7-10 days, but also no sign of stormy weather either. Just a typical mix of clouds, showers, and occasional sunny days. The ECMWF ensembles show temps cooling a bit more the next 10+ days; that would be normal for late October

Speaking of cooler temps, La Nina is now into the MODERATE category in the equatorial Pacific. Forecasters are confident this will be the case for upcoming Winter 2020-21. I'm working on the general winter outlook and should have it finished up next week. I'm feeling very confident we should see quite a bit more action than last winter. Remember how boring it was? Almost no storms and no lowland snow until mid-March! To whet your appetite a bit...take a look at the past 20 winters in Portland.

And farther back in time...seems like we have leveled off the past three decades a bit. Last winter finished off the 2010s decade; a new weather decade starts this winter. Snow measurements were taken at the NW corner of PDX up until 1996, then moved to Parkrose (near Sandy Blvd) for the past 24 years.

Last winter was very mild, some of my annuals from the previous summer made it through.

My banana bushes/tree, which most winters die down to the ground, made it to the 2nd story roofline by late August!

In fact last winter EVERY SINGLE DAY made it to at least 40 degrees for a high. It's been 18 years since we've seen a winter without a 30-something degree day.