Sunday Morning Forecast Still On Track; Flakes Mixed In Rain For Most of Us

January 23, 2021

6pm Saturday…

I’m not at work today, busy getting all the snow preps done! Just kidding, I left my snow shovel at work for a promo shoot. I’ve been confident I won’t need it tomorrow morning, even at 1,000′. I don’t shovel an inch or so…

This little “event” coming up late tonight and tomorrow morning has been solid forecast-wise for four days! Nothing has changed in either models or our thinking. The previous post is still valid.

Sunday Highlights

  • We will all wake up (west of the Cascades) to rain or a mix of snow/rain at the lowest elevations. Precipitation arrives sometime after 3am…timing has moved up a bit.
  • If you live near/above 1,000′, there’s a decent chance you get at least a dusting on the ground. If you live below 1,000′ IN THE METRO AREA, I’d be surprised if anything sticks. The “1,000 ft” is an approximation, we can’t actually forecast snow level with precision more than 500-1,000′. See rant below…
  • Whatever happens will be done by noon, then temps rise a few degrees (up to around 40 or so) and steady rain changes to light afternoon showers. Nothing interesting happens the 2nd half of the day
  • If you live in the lowest elevations (90% of us), your life should continue as normal tomorrow. Except for that COVID thing, but you know what I mean. Normal for these times.
  • If you live well above 1,000′ (like 1,500′ or higher), you’ll have some nice snow to enjoy tomorrow! Probably 1-4″ up there. This includes northern Clark County foothills, the hills above Scappoose and St. Helens, and above Kalama, Longview etc…

This graphic summarizes it well

Tomorrow night and Monday we’ll see very light showers; could be mixed at times, but leftover wet roads freezing in a few spots Monday morning MIGHT be a bigger issue. I’ll tackle that tomorrow

SOME OTHER INFO

Latest ECMWF snow forecast looks the same as it has for the past few days

This will be the first test of IBM’s 4km (higher resolution) GRAF model for us. Actually it nailed the 1/2″ last March, but this is the longer range version (to 3 days) that came out last summer. It says “FORGET IT” in the lowest elevations.

The “reliable for the past 20+ years” WRF-GFS (UW) is reasonable…a bit of snow most areas above 1,000′. But all lowest elevations…forget it. I’ve noticed it tends to “over snow” these marginal events. So we’ll see if hills around Happy Valley and central Clark county picks up measurable snow… This is the highest resolution model we have for our area. 1.33km! This means grid spacing is so tight that the model’s terrain includes features not seen in coarser resolutions. You can see Chehalem Mtn, the West Hills, outer SE metro area buttes, and south Salem hills. Note this one can also clearly “see” the Gorge. Little or no snow on I-84 in the Gorge tomorrow.

Just taking a look at the text data from ECMWF says we’re coolest before midnight with the partly cloudy skies we’re seeing now, then a light southerly breeze plus cloud cover means temps actually rise a bit toward sunrise. Precipitation is quite light on this model as well. Only .10 to .20″ by noon, that’s not going to drag the snow level down very far. NOTE THAT TYPICALLY THE -3 to -4 850mb temps would mean a sticking snow level up around 2,000′. We’re lucky to see sticking snow below that elevation briefly tomorrow morning.

WE CAN’T FORECAST SNOW LEVELS IN 100′ INCREMENTS

You may remember my rant about snow level forecasting in the past. I cringed when the NWS folks issued a Winter Weather Advisory for elevations ABOVE 700′ in the metro area for Sunday. I have no problem with NWS; they all work hard and do a great job. But when is the last time you heard a Mt. Hood snow forecast of “3,700′ tomorrow”. Or “expect a 4,300′ snow level dropping to 2,700′ late this evening”. We don’t, and shouldn’t in this case either. That’s because snow level is also highly dependent on precipitation intensity. Heavier precipitation = lower snow levels generally. So don’t read the Winter Weather Advisory as “you won’t get sticking snow at 600′ but will at 800 ft”. Instead, I wouldn’t be surprised if some neighborhood gets sticking snow (somewhere) to 500′ Sunday morning, but somewhere else you get nothing at 1,000′. That’s why I use the “near and above 1,000 ft.” terminology.

So insert your eyeroll here and “oh geez, Mark is throwing a fit about THIS again?” One example below is from a blog post in 2016. Setup was a bit different, but same issue


We’re doing people a disservice by implying we have more accuracy than we do.  

This morning is a perfect example of why forecasters (and the NWS) shouldn’t be forecasting snow level in increments below 1,000′ in a snow shower pattern.  A snapshot at 8:30am:  Staley’s Jct. on U.S. 26 west of Banks…elevation 200 feet.  A snowy road and maybe a half inch on the ground:

us26-at-staleys-junction3_pid2985

At the SAME ELEVATION, but 15 miles east on the west side of Beaverton…all bare and wet with no snow in sight:

26bethany_pid524

Then over on the eastside of the metro area just above Sandy…at 1,200′.  NO SNOW. The white stuff is left over from yesterday’s hail/graupel showers.

us26-at-firwood-rd_pid2331

So what was the “snow level” at 9am???  Under the heavy showers it was near sea level, where very little precipitation fell it was higher, up around 1,500′.  


Alright, I’ll be on TV tomorrow evening at 5/10/11pm, taking a close look at Monday and Tuesday. Likely a couple more “near misses” for those days.

Chief Meteorologist Mark Nelsen


Sunday Morning: First Snow Sighting Of Winter For Many of Us

January 21, 2021

6pm Thursday…

If you haven’t left the lowlands this winter, most likely you also haven’t seen a single snowflake. February is less than 10 days away! That’s unusual in our climate. Typically we have a close call or two, if not real sticking snow, by this point in the winter. Not this year, it’s been very mild. But if you are up before 10am Sunday, it appears there’s a decent chance you will at least SEE snowflakes in the air. Sledding in the lowlands? Unlikely.

For the short attention span (TLDR) folks…

Winter Weather Highlights

  • Between 4-8am Sunday, precipitation arrives across NW Oregon and SW Washington. Most likely it’ll be a rain/snow mix in the lowest elevations (where most of us live)
  • There’s a decent chance it falls as mainly snow for at least a few hours 7am-10am, even in the lowest elevations. It could get very exciting weather-wise for a few hours!
  • Temperatures remain ABOVE freezing Saturday night and Sunday = little or no sticking. If it falls heavily enough, it might briefly accumulate on cars/barkdust etc…
  • IF you live up around 1,000′ and above, there’s a better chance your neighborhood turns totally white for a few hours.
  • IF you live around 1,500′ and above, expect 1-3″ Sunday morning through midday. There are no spots in the metro area that low.
  • Highways/roads will remain snow-free Sunday in the metro area, except at/above 1,000′ where they could briefly turn snow covered.

THIS SHOULD BE A “CONVERSATIONAL SNOW” EVENT FOR THE LOWEST ELEVATIONS. That means everyone will be talking about it; plus posting Instagram/Facebook pictures of their dog/cat/pig/chicken/duck running wildly about outside, but it won’t affect our lives otherwise.


TECHNICAL DETAILS

A cool upper-level trough (the first of several) is sliding down north to south along the West Coast. This system is headed for California and far enough offshore that we’re seeing almost no showers inland. A mainly dry and cool airmass settles over us Friday & Saturday. Drier air filtering in from Canada gives us LOTS of sunshine Saturday; enjoy that day after a cold start. We’re not getting a “cold blast of air” by any means, just a bit colder.

By Saturday night another cold upper-level trough is sliding south along the BC coastline. A cold front then moves inland midday Sunday. Here’s a loop from the ECMWF model showing the movement from 1am to 7pm Sunday. Not exactly a “storm” eh? All models have been showing this scenario for several days and all agree on the timing; pretty good for 3-5 days ahead of time.

Freezing levels Sunday morning will be up around 2,000′ or so with this system, which typically means we might see snowflakes down to maybe 1,000′ and just a rainy Sunday morning in the lowlands. But a few things are different Sunday morning which should bring those flakes lower:

  1. Overnight cooling, while minimal, means this system comes in at the coldest time of day
  2. No significant “warming” onshore wind. There’s no cold/dry wind blowing out of the Gorge, but there’s no push of warmer air before 10am either. It should be mainly calm Sunday morning, at least for a few hours.
  3. There are signs we get a burst of heavier precipitation between 7-10am. Heavier precip = better chance for flakes to survive a longer fall through the atmosphere

These all point to a setup where snowflakes may survive falling all the way down to the valley floors west of the Cascades (less likely along the coastline) for a few hours Sunday morning. The reliable WRF-GFS model from UW shows the above freezing temps through Saturday night. At 4am it’s in the mid-upper 30s in Portland. This isn’t a setup where precipitation arrives at sunrise after a frozen night.

But as precipitation starts falling, look how surface temp drops to 33-36 degree range

Then 10am

That’s pretty much a snow sounding; at/below freezing except for the lowest 500′ or so. By 1pm Sunday, the cold front has passed, mixing (warming) the lowest layer of the atmosphere with a southwest or westerly wind. At that point we’ll just see rain or mixed rain/snow showers. It appears we have .25 to .50″ precipitation to work with, enough for 1-3″ in higher elevations where this falls as snow and sticks.

Models ALWAYS struggle with predicting snow totals in these marginal events. This morning’s ECMWF model continues the “little or no sticking snow” idea; you need to be up/above 1,000′ (or 1,500′) to make a snowman this time around

Note the coarse resolution here. I’ve purposely left it “unsmoothed” so you can see the model resolution. It doesn’t see the West Hills or Chehalem Mtn. at this 9 kilometer resolution. It also doesn’t “see” the Columbia River gap between Woodland and Longview, thus painting a bunch of snow for Kalama, Rainier, Longview, & St. Helens. It “thinks” the hills of Columbia county OR just merge into the hills above Kalama & Woodland. Higher resolution models (4km & lower) DO show those features, but we don’t have those today. They run just 72 hours out in time and only cover to 4am Sunday.

Alright, so that’s your first “big snow chance” for this season. That was a joke, it’s not a big snow chance. We MIGHT be close again early next week (either Monday morning or Tuesday night), but we can discuss later.

I still want to be clear that this is the not the beginning of a cold/snowy weather pattern. Sure, we’ll be getting more regular frost and overnight freezing. But no sign of an arctic blast through at least the first few days of February.

I probably won’t post tomorrow considering how minor this event will be; time to get out and enjoy the wintry outdoors. I’ll definitely be back with an update Saturday.

Chief Meteorologist Mark Nelsen


Warm Winter Records & Low Elevation Snow Thoughts

January 19, 2021

7pm Tuesday…

Just a brief post this time around to assist in your weekend planning.

It has been another mild day…back in the 50s. Hard to believe it took until January 19th to see our first frost of the new year too! We dropped to 31 in Portland this morning.

From the beginning of meteorological winter (December 1st) to this point, Portland has never seen so many 50+ degree days! It’s a record that goes back 80+ years. Salem hasn’t seen this many in 100+ years, same thing at Astoria. Even in Central Oregon, Redmond has seen more 50 degree days than any winter (so far) in the past 30 years. It’s truly been a mild winter to remember…so far.

The general plan continues the same through the next 8-10 days. Warm upper-level ridging is replaced by cool upper-level troughs dropping down over us Thursday, Sunday, and possibly next Tuesday. Beyond that time the troughing either weakens or shifts farther west = slightly warmer which would mostly eliminate the main chance for low-elevation snow. So for January it appears our “big chance” near the valley floor will be Sunday-Tuesday. But don’t get out the sleds yet…

In case that was already enough technical talk for you, I think these two graphics cover it well:

What we DON’T expect…

and what we DO expect…

For the rest of this month, it appears your plants are safe from a big arctic freeze. That’s still not in the cards. Just looking at the next two weeks (Euro model ensemble high/low average) you can see we “bottom out” Sunday through Tuesday, then rise back to around average again late next week. We may not be headed into a prolonged period of cooler than average weather. We’ll see.

Alright, how are we looking for Sunday at this point?

As you can see above, I think there’s a good chance that we may wake up to rain/snow mix even at the lowest elevations. But all models show temps near/above freezing that morning with a light southerly flow; we’re not going to have a snowy metro area locked in snow Sunday.

If you live at/above 1,000′ it could be a nice little 1-3″ snow event Sunday. Best bet would be northern Clark county hills along with higher parts of Columbia county (St. Helens/Scappoose) and Coast Range (Vernonia). Maybe central/eastern Gorge too. Possibly a dusting to an inch in Portland’s West Hills…maybe.

We will cover all this in more detail as we get closer…we’re still five days away.

Chief Meteorologist Mark Nelsen


Mild Winter So Far, But Colder With Snow Close to Sea Level Ahead

January 17, 2021

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 ECMWF ensemble forecasts for snow. About 1/3 to 1/2 produce “sleddable” snow in the Portland metro area 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


Pineapple Express Delivers; Flooding and Wind Recap Plus Brief Look Ahead

January 13, 2021

9:30pm Wednesday…

We just experienced the stormiest weather we’ve seen so far this very benign winter. It was quite a triumph of weather forecast models too. They nailed the rain totals plus end time of that heavy rain.

A few points:

  1. Portland broke a record for daily rain yesterday
  2. Tuesday’s rain was the most we’ve seen in one day in over 3 years!
  3. Over a 100,000 power customers lost power in the metro area as a cold front moved through early today

Surprisingly uniform rain totals at the official reporting locations

Of course hills pick up more precipitation; there were some spots in the metro area that saw up to 4″ of rain. But the big totals were in the mountains; look at all those 8″+ spots!

By the way, the south wind and warm airmass pushed Portland to 61 degrees right after midnight, tying a record high for the date. That’s when things turned wild. The one surprise was last night’s cold front; it was stronger than expected. Strong WEST wind came in behind it between midnight and 1am. Peak metro gusts…

Of course you are probably wondering how we ended up with 94,000 PGE customers out of power with gusts only up around 35-50 mph? Two thoughts on that:

  1. Two days of soaking rain saturated the ground, loosening roots and allowing trees fall over easier than if ground was dry
  2. I haven’t seen a strong west wind like this since March 2011. That month we saw a rare westerly gust to 55mph at PDX. Strong wind from an “unusual” direction can easily give us more damage than expected

What’s Ahead?

We’ve got a lot of SLOW weather the next 7 days. Upper-level ridging sticks around now through the middle of next week. Only very weak systems slide through Friday, Sunday, and maybe next Tuesday. First, you can see the 500mb map for Saturday…ridging over the western USA

Then Wednesday

But a change late next week; ridging moves farther west and weakens. Looks like we’re heading into a cooler flow of air from the northwest.

That was the ECMWF for Friday the 22nd. Beyond this point is where models diverge. Will a much sharper upper-level ridge build over the Gulf of Alaska and allow a cold trough to dig south over us? Or will westerly flow dominate? Regardless, it’s obvious we’re headed into a cooler pattern starting around the 20th. We’ve been seeing this pattern change for almost a week! Look at the ECMWF ensemble chart for 850mb temps over the next two weeks (the rest of January). You see the sudden change on the 20th.

The “0” line means snow down to about Government Camp; notice that for about 10 days starting the 20th the sticking snow level should be near/below the passes. We haven’t seen that yet this season. Could be a great snow pattern for the Cascades and the foothills will finally start seeing some snow!

Summary

  • The Pacific Northwest will likely enter the first cool weather pattern of winter; starting late next week
  • It’s too early to know how low snow could fall, the change is still 8-9 days away
  • No, we don’t know if it’s going to snow in the lowlands the 2nd half of January. But for the first time this winter, yes, I’m saying…”there’s a chance”. It’s bizarre that I haven’t mentioned that phrase; we’re 3/4 of the way through winter west of the Cascades!
  • If something fun (snow and/or cold) is on the way, it would be the last full week of the month (23rd-31st), not next week

Notice 20 of the 51 ECMWF ensembles forecast some sort of real snow in Portland sometime in the next two weeks.

That’s it for this evening. I’m off the next three days and will have plenty of time for a fresh post Sunday evening.

Chief Meteorologist Mark Nelsen


Lots of Rain & Wind Ahead; Then A Drier MLK Weekend

January 10, 2021

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 (Sunday the 24th), 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


Looking like El Niño conditions more than La Niña so far this cold season

January 4, 2021

8pm Monday…

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.

Chief Meteorologist Mark Nelsen