A cold and wet midweek, but sunshine and first frost on the way

8pm Wednesday…

What a cold couple of days. We only hit 53 in Portland yesterday, then 51 today. Most of the day was showery and in the 40s. Yep, you aren’t crazy, that’s a typical mild winter day around here. That says two things: first is that our winters are pretty darn mild, and second is that it was unusually chilly today. We picked up about 1/3″ of rain, putting us right up around normal for this time of year.

Let’s discuss rain & (lack of) rain ahead, mountain snow, and frosty weather.

RAIN

We picked up about 1/3″ of rain at PDX today, putting us right up around normal for the month so far. But I see very little rain in the next 5-6 days. An “Omega Block” is dominating the far eastern Pacific. That’s because the upper-level flow in the atmosphere, viewed from space, looks like the Greek letter Ω (Omega)

These Omega blocks are often persistent for at least a few days with the strong high pressure blocking storms from approaching the west coast of North America. In this case a cold upper-level trough has dropped down the east side of the high pressure. Yes, this IS the snow/cold pattern for us in winter. This same setup between Thanksgiving and early March could bring snow to sea level. The ridge of high pressure moves much closer this weekend. That’s cool-ish northerly flow and dry air = lots of sunshine!

By NEXT Thursday, the block has broken down and a mild/wet pattern is about to resume.

This general setup is showing up in all the long-range modeling. Check out the 24 hour precip forecast from the Euro ensembles; totally dry for about 5-6 days, then LOTS of very wet members (each horizontal line is a member) for that first weekend in November. Right on cue, November looking mild and wet to start.

(kptv)

So get any outdoor fun/chores/projects done by Tuesday, and enjoy this weekend.

MOUNTAIN SNOW

The first snowfall of the season arrived at Government Camp late yesterday, just one day later than last year.

So far about 6″ has fallen at Government Camp, with 12-15″ higher up at the ski areas.

Expect passes to totally freeze up tonight, then much better driving (mainly wet) by tomorrow afternoon. There will not be any more snow at pass elevation from tomorrow through at least the 2nd or 3rd of November. Snow if October is the norm…Government Camp averages 5″ this month. Every once in awhile we get a big dumping though. I remember my very first year forecasting out of college (October 1991), 2 feet fell and we got REAL excited about a big ski season.

Well, that was an El Niño year and the rest of the season was very mild and drier than normal. That cemented in my mind that October weather has no positive correlation to what happens during the following winter. The snow currently on the ground even way up at Timberline will mostly melt over the next week or so.

FIRST FROSTS

It’s time…typically west of the Cascades we get a first frost somewhere between mid-October and mid-November. Take a look at recent years at Hillsboro, a colder spot in the metro area

And then Portland numbers (text and then bars in blue) on the same graphic. Some years it’s the same time, but most years the city sees a first frost several weeks later.

Almost EVERY SINGLE NIGHT has been warmer than normal so far this month…that includes every red number below.

https://529123ffb3e54af429b49777bc7fa78b.safeframe.googlesyndication.com/safeframe/1-0-40/html/container.html

So it’s going to be quite a change this next week as skies clear out and temperatures drop. A very dry airmass arrives Friday afternoon on gusty northerly/easterly wind. Models are pushing dewpoints down into the 30s and 20s. That’s dry enough to mostly keep fog away, plus easterly gradients through the Gorge are between 4 and 6 millibars from Saturday through next Tuesday. This should keep the low levels dry. Calm spots will drop into the upper 20s in this setup, beginning Saturday and Sunday mornings. This is what we are forecasting IN CALM AREAS OF THE CITY

That’s it for this evening. Enjoy the upcoming dry weather!

Winter 2023-2024: El Niño isn’t always bad news in the Cascades

8pm…

Yesterday I covered all the basics of this upcoming winter and what it could mean down in the lower elevations where most of us live. You should read that blog post first to get an idea of what we generally expect across the Pacific Northwest. This post is all about what we might see in the Cascades; especially important for the ski/snowboard/snowplay industry.

First…

EL NINO WINTERS ARE RARELY SKI SEASON “DISASTERS”

The phrase “EL NINO” often strikes fear into the hearts of Northwest skiers and is a somewhat deserved reputation. That’s because we tend to see warmer and drier than average weather across the northern half of the Pacific Northwest as mentioned in yesterday’s post. You’ve likely heard that California gets slammed by lots of stormy/wet weather many of these winters (but not all!). You can find a list of these winters here: https://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php. El Niño episodes are in red. Take a look at the last 7 El Niño winters (since 2000) combined…the precipitation anomaly. Warm colors mean drier than average, cool colors = wetter than average. Strong DRY signal here for December to March.

https://4425c8f915318faf5c68f19f8194e5eb.safeframe.googlesyndication.com/safeframe/1-0-40/html/container.html

Temperature anomaly for the same years; a clear signal for warmer than normal!

(kptv)

So let’s take a look at Cascade snowfall during the 25 El Niño winters we have seen since the early 1950s at Government Camp. Average yearly accumulation (for any year) is 254″ (click for full-size)

Government Camp snowfall in El Niño winters

That’s not good news. A couple thoughts:

• EVERY EL NIÑO SINCE 1970 HAS PRODUCED BELOW NORMAL WINTER SNOWFALL AT 4,000′ ON MT. HOOD
• ONLY A FEW YEARS ARE REALLY BAD (WE REMEMBER THOSE!), MOST JUST HAVE LESS FREQUENT SNOWFALL AND MORE RAIN/SNOW EVENTS AT THAT ELEVATION

There is a downward trend as well through the entire period; although 26 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 (global warming) 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 yearly 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 but still cold enough up high.
• El Niños are more reasonable at a higher elevation. That’s because we tend to be warmer in El Niño winters with warmer storms.
• At higher elevations a few El Niño winters have actually been snowier than normal. Another reason to not freak out about the upcoming winter ski season. You will likely need to spend more time this coming winter on the higher parts of your favorite resort.
• 1982-83 is a strange 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 Niño winters…not as bad.

https://4425c8f915318faf5c68f19f8194e5eb.safeframe.googlesyndication.com/safeframe/1-0-40/html/container.html

There are some years (06-07, 15-16, 18-19) when plenty of snow fell during this time. Drilling down a bit further, just looking at November+December snow below. That’s when we want to see a solid base develop. Most years are at least “okay”. An example is December 2018. Little or no snow on the ground up there early in the month, but just in time for Christmas Break a dumping arrived. Whew! Ignore the M on the chart, that’s a different subject (Modoki El Niños). So even a drier/warmer than normal January/February can be offset by a one-month dumping of snow in December. That 3-6 foot base can sustain the ski season, although it doesn’t help the water supply much.

So perception of winter up in the mountains will be based on two things: timing of snowfall, and if we get regular rounds of good quality snowfall.

SUMMARY

• There is an increased chance that this year will be more challenging; it’ll be tougher to find regular powder days in the mountains. When it happens? Seize the day and get on the slopes quickly!
• The best chance for good snow this year will be up high, most likely many of our systems will be a bit warmer than “normal”
• It’s unlikely we have a terrible ski season as we saw in 91-92, 04-05, and 14-15, BUT, the risk for a train-wreck season is higher than normal
• We can get a surprise. The end of the last El Niño season (18-19) featured a strange/cold northerly flow for 5 weeks in February and early March. It ended up being the snowiest February during an El Niño at Government Camp!
• Snowpack in much of the Oregon and Washington Cascades will likely be below normal this winter and that could lead to water supply issues later next spring/summer in some areas

Winter 2023-2024: El Niño is back, but will this one be different?

9pm Monday…

It’s time to take a look at this upcoming winter. Of course we can’t forecast with any sort of detail more than 7-10 days ahead of time. but we can glean a few general ideas each year. Buckle up, let’s call this “my thoughts” for the upcoming winter since I’ve got a few tidbits for you. This is NOT a forecast or even an outlook. First, a quick recap of the past two winters…

Winter 2022-2023 Last winter was a 3rd consecutive “La Niña” winter, which means for the 3rd consecutive year the tropical Pacific Ocean was cooler than average. We ended up a little cooler than normal and slightly dry. Here in the metro area of course me mainly remember two things: the very cold air leading into Christmas with mainly freezing rain, then the snowstorm 2nd half of February

Winter 2021-2022 Two winters back was a 2nd consecutive “La Niña” winter; things got a little crazy with lots of foothill/mountain snow the 2nd half of December, but then real quiet midwinter. Most of Portland’s snowfall was in late December.

LOOKING AHEAD

It’s hard to believe, but this will be my 32nd winter forecasting here in NW Oregon; I started forecasting professionally in October 1991 straight out of the University of Washington. Many things have changed since then, but there is still a LOT we don’t know about our climate and seasonal shifts in weather. Typically we focus on the La Niña/El Niño (ENSO) oscillation across the tropical Pacific and what that means for northern hemisphere winters. That is still the case, but other factors play into our winters such as the “Pacific Decadal Oscillation” warming oceans. So each winter is different and lots more research is needed. Disclaimer: I’m dropping the “ñ” from this point forward in this post because I get tired of typing ALT-0241 over and over. Just know the proper spelling in Spanish is with the ñ.

We are already in an El Nino episode and that continues through the winter. Right now it’s a “moderate” El Nino based on the “Oceanic Nino Index”. That index may make it into the “strong” category. Anything above +0.5 on this chart is considered El Nino, above +1.5 is STRONG. Notice all model forecasts peak and then weaken the event by next spring

We tend to see a changed north Pacific jet stream during El Nino cool seasons, due to the mass of warm water to the south positioned a bit farther east than normal, plus some other changes. Typically the Pacific jet stream flows generally west to east and runs into the northern half of the USA West Coast, especially during La Nina winters. Thus the heaviest winter rains tend to fall in the Pacific Northwest, as opposed to California. There are exceptions, like this past winter when California got hammered with rain/snow during a La Nina winter; unusual.

La Nina Jet Stream

But during most (not all!) El Nino winters we see the normally strong jet stream in the western/central Pacific push farther east towards North America. It’s barely noticeable on these graphics because it’s a 3-month average.

https://439c8604e5d22837907de2ce5643431e.safeframe.googlesyndication.com/safeframe/1-0-40/html/container.html

When that happens, we see more wet systems into California AND more areas of upper-level high pressure pop up over western Canada. This causes a bit of a “split flow” in the Eastern Pacific, shunting 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. Remember this is all what is “typical”.

Notice the Pacific Northwest sees a mix of weather. The northern part is strongly influenced by the upper-level high in Canada, 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 in many El Nino years.

https://439c8604e5d22837907de2ce5643431e.safeframe.googlesyndication.com/safeframe/1-0-40/html/container.html

It’s important to point out that though many El Nino winters follow this pattern, but 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 (Winter 2015-16). Both 1982-83 and 1997-98 (strongest since 1950) both featured near or above normal rainfall even up here in Portland.

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 and possibly drier than normal winter means no snow in the lowlands; not true at all. Check out the last 10 El Nino winters:

We saw snow storms in January 2007, January 1998, & February 1995. And who can forget the fiasco in late December 2009…the surprise (terrible forecast) snow event that gave us the worst evening commute in many years! But there is one common theme in each of these snow events; they all lasted just a short time, then the mild winter resumed. I distinctly remember shoveling feet of drifted snow in eastern Multnomah county 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 (Winter 2016-17), 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. The last 17 winters at Troutdale airport below. Any day with an easterly gust over 25 mph counts

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 events in 2009-10, 2014-15, and 2015-16.

SUMMARY

• 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, you should have a plan for that
• Widespread regional flooding is unlikely this winter, more action heads south into California
• Expect a bit more east wind than normal this year in usual spots east metro and Gorge

THE WILDCARDS THIS YEAR

1. Warmer than average ocean water across much of Pacific (and globe!)
2. The “MEI” index is significantly weaker for now, indicating this El Nino may not be as strong as it appears

One item that’s different than previous El Ninos is the widespread warmth across most of the global oceans. Of course I mean warmth compared to normal. There is some speculation that this El Nino could be different because that large area of very warm water in the equatorial Pacific is surround by lots of warm water elsewhere. Could that prompt a different atmospheric response this year? Maybe upper level ridging in a different place instead of western Canada? Look at almost the entire northern Pacific with well above normal sea surface temps! In a most El Nino events, the warmth in the equatorial Pacific really sticks out. This year that warmth is surrounded by many areas of warmer than normal ocean waters (most of Atlantic and almost all of north Pacific).

The Oceanic Nino Index chart I referenced above has a related cousin. The “Multivariate Index” takes both oceanic AND atmospheric variables into account; it’s considered a more “thorough” view of this phenomenon. Notice how much weaker the event is (so far) using this index. More like 1986-87, and 1991-92. Significantly weaker than the strong event in 2015-16.

The weak/moderate MEI El Nino events since 2000 look like this for cold season precipitation; very dry in the Pacific Northwest. So could we have a drought winter on the way? Hmmm…

That’s a much different look than the 3 strong El Nino wet seasons…wetter than normal.

In a future post (Tuesday), I’ll take a look at what we might see in the Cascades and how this all might affect the ski season.

Tornado in La Center Today

10pm Wednesday…

Once or twice a year we hear about a (usually) weak tornado in northwest Oregon or southwest Washington. It happened again today. In fact we first heard about it while recording our weekly weather podcast.

(kptv)

I think Katie was “passed a note” around the 22 minute mark, you can watch it here (lower player): https://www.kptv.com/podcasts/weather/

Well, this one was not only weak, it was VERY weak. Here’s the story from La Center

The damage? A few shingles missing, trash cans turned over, and a trampoline thrown around. Oh, and don’t forget the basketball hoop blown down! The official storm report from the Portland NWS office…

(Mark Nelsen | kptv)

EF-0 tornadoes are the norm these past few years. Although I recall that Sandy tornado did quite a bit of damage in the Cherryville area last October

(kptv)

Of course the vast majority of tornadoes in our area are EF-0 to EF-1

(kptv)

Speaking of October, there IS a bit of a tornado season west of the Cascades. September/October and again in late spring. I mean, this sure isn’t “tornado alley”, but just an interesting little tidbit of twister info.

https://97598b0ab11a09b5c91d78eadc17b74b.safeframe.googlesyndication.com/safeframe/1-0-40/html/container.html

(kptv)

There was just a bit of snow at Timberline Lodge (6,000 ft. elevation) this morning for the first time this season. It was only a dusting. In some years significant snow falls in the high Cascades in October; but that doesn’t appear to be the case for the next week or so. Take a look at the ECMWF 500mb height anomaly for the next week

(kptv)

Then for days 8-14, which takes us close to the end of the month. Higher than average heights = warmer than normal October weather. Not necessarily dry, but any systems coming through will be relatively warm for the next 1-2 weeks.

(kptv)

Those were ensemble average maps from the ECMWF. The GFS ensemble average is similar for days 9-16

That’s it for this evening. Enjoy a warm and dry Thursday with lots of afternoon sunshine!

October “heat” along the coastline today; plus record-setting Saturday for Portland

11pm Friday…

I loved the crystal clear blue sky today, the bright sunshine, and the warm evening. Not a cloud in the sky late this afternoon across Oregon, Washington, AND Idaho; quite rare anytime of the year.

GOES18 Satellite Image(Mark Nelsen | kptv)

But the warmth WAS a little strange for this time of year wasn’t it? Take a look at our 3 coastal cameras at 4pm:

(kptv)

(kptv)

(kptv)

Our forecast and modeling of this fall east wind event was perfect. Sure enough, the easterly wind made it all the way to the coastline, pushing temperatures into the 80s. Newport even hit 90!

Wx Blog(kptv)

But that is not a record for October. Most inland locations have hit 90 at some point in the past in October. Coastal spots are similar

(kptv)

The easterly wind that brings us the warmth is dying along the coastline this evening. A good measure of that offshore flow strength is the pressure difference from Spokane WA to North Bend OR. Earlier today it was up to 12 millibars. Now it’s down to 7.6 millibars. The gradient through the Gorge (better measure for east wind in metro only) peaked around 6 millibars earlier and now is also around 4.7 millibars. This means wind keeps flowing in east metro areas and the western Gorge tonight through midday tomorrow, but dies in all other spots. The change to southerly wind drops the coastline 20-25 degrees Saturday

Oregon beaches Saturday(kptv)

That wind kept Troutdale at/above 68 degrees last night, the warmest October low temperature on record there. Expect a similar reading tonight. All other calm areas drop into the 50s by sunrise. Numbers should end up similar to what we saw this morning

(kptv)

So the wind dies down tomorrow and we have another day in the mid 80s in the metro area. Then the loss of that easterly flow Sunday keeps us in the 70s. A weak cold front moves inland Monday for a rainy/cloudy day and temperatures closer to 60. A little bit of something for everyone the next 3 days. Enjoy your weekend!

(kptv)

Big warm up this week plus fire season wraps up

7pm Tuesday…

October is here and colors are beginning to appear on trees here in the lowlands. I was up around 3,000′ in the Cascades southwest of Hood River last weekend and the flaming red vine maples were stunning under a blue sky. Of course winter arrives much earlier up there so those leaves will be gone soon.

Fall is typically a mix of warm/sunny weather and rainy/cloudy/cool weather and that’s what we’ve been seeing this year so far. Yesterday was wet/drippy, but very warm weather is on tap for a few days. Then it’s back to wet/cool for at least the early part of NEXT week.

KEY POINTS

• The next chance for rain for most of us is not until Monday of next week. You’ve got 5 dry days ahead!
• Temperatures warm dramatically Thursday-Saturday, but no record highs. Lots of sunshine too
• A gusty east wind Thursday and Friday won’t be a problem fire-wise since the hills have been soaked by rain
• Fire season is ending with well below normal acreage burned in the Pacific Northwest…good news!

September ended pretty darn normal, of course a very warm first half and cooler than normal 2nd half.

(kptv)

And just in time, plenty of showers/rain scattered over the past 10 days has started to moisten the parched soil a bit. Portland has picked up about 1.50″ rain, but over 2.00″ fell down around Salem. Most important, the mountains around us have picked up substantially more. Some foothill and west slope locations along the Cascades have seen 2-4″ rain

(kptv)

The leftover wildfires on the west slopes of the Cascades are just smoldering a bit under high humidity and rain. There has been no significant acreage burned for at least a week. Fire Season 2023 is pretty much over now folks and we got lucky once again this year. Only about ¼ of the typical acreage burned across the PACNW. Every spring we run stories about how it could be a bad fire season for whatever reason. Sure, a warm/dry spring (this May) can set the stage for a bad fire season, but what really matters is how the weather progresses July-September. This year we had cooling and/or showers following a couple of big lightning events, keeping things under control. Plus it seems that we had far less lightning than normal in July and early August. The sudden cooling/showers in mid-September kept us from having any blowups right at the end of the season and we had no gusty east wind events before those rains arrived. Of course this means we didn’t have to deal with any power shutoffs in the late summer or early fall.

(kptv)

WHAT’S AHEAD?

We have some fantastic weather on tap the rest of the week. A strengthening upper level ridge of high pressure is developing just offshore and now has shut off the rain as it edges closer. It’ll reach max strength right over the top of us Thursday

(Mark Nelsen | kptv)

It lingers overhead, although weakens through Sunday. By Sunday afternoon you see a cool trough and westerly flow is ready to run into the Pacific Northwest

(Mark Nelsen | kptv)

How warm is the ridge? It’s quite similar to several events we saw during last year’s warmest ever October. In fact 7 daily record highs were set at PDX in October last year. This time of course it’s only happening once during the month. 850mb temps around +19 to +20 both Thursday and Friday afternoon will be accompanied by easterly low level flow. The thick blue line on the WRF-GFS cross-section is around 5,000′. Time runs from right to left on these charts. You see the easterly flow developing overhead tomorrow night, then surfacing Thursday afternoon at sea level. The pressure gradient across the Cascades (The Dalles to Troutdale) reaches 4 to 5 millibars Friday morning, then goes flat again by Saturday afternoon; this is just a 2 day offshore wind flow event

(Mark Nelsen | kptv)

Just like last October, this should give us 2-3 days at/above 80 degrees. No records though this time

(kptv)

Overnight lows drop into the low-mid 50s in the city and 40s in outlying areas. It’s that briefly weird time of year when you want heat in the morning (possibly), but then want to open the windows in the afternoon to let in the warm breezes.

By next Tuesday, a westerly flow overhead has returned the clouds and rain to the region. That said, there are hints it’ll only be one or two systems and then ridging might come back for a day or two.

(Mark Nelsen | kptv)

That’s it for this evening.

Don’t forget that we are now producing a weekly weather podcast. As far as I’m aware this is the only weather podcast in the region. Last week we had a GREAT discussion about the big southerly windstorms we get in our region. Just one graphic for you here…

(kptv)

You can subscribe to the audio version of the podcast on your favorite app, but nowadays since we often incorporate graphics I suggest you watch it on this page: https://www.kptv.com/podcasts/weather/. The 2nd link is the video version. If you have the First Alert Weather app, then a push alert comes out each time a new podcast is available

(kptv)