Colder Weather Next Week: Snow Update

November 30, 2016

9:30pm Wednesday…

Will it snow in Portland this coming Monday or Tuesday?  Sure, maybe in the air, but it’ll be far tougher to get more than a dusting down to the valley floor.  My thinking hasn’t changed much the past two days because models have been doing a very good job with the evolution of the weather pattern over the next week.  The end result is a cold upper-level trough descending on the Western USA


A strong cold front moves through the region the 1st half of Sunday.  Behind it, the snow level (the lowest level in the atmosphere in which snow sticks) drops to around 1,500′ the rest of the day Sunday.  So the Coast Range passes may see some snow come and go during the day, and of course the Hoodland corridor from Brightwood to Rhododendron should see some snow too.  Models haven’t been showing temperatures cold enough for sticking snow lower than that Sunday, so I’m quite confident with this first part of the forecast.  We’ll see showers off/on Sunday with a few flake possibly mixed in at times here in the lowest elevations.  Temperatures hover in the low-mid 40s.

It gets more interesting Sunday night and Monday as cooler air continues pouring in.  By Monday morning, any decent showers should be able to drop a dusting down to around 1,000.  I’m pretty confident that if you live above 1,000′ you could wake up to at least a light coating of snow.  Here in the city it’s more likely we’ll just have scattered showers milling about Monday morning with any of them containing snow too.  Temps remain ABOVE freezing through the day Monday below 1,500′.  The ECMWF and the GEM both show onshore low-level flow and a mixing southerly wind continuing through Monday AM.  That generally kills the lowest elevation snow chances pretty well.  But not always, see the next sentence.

The one item I’m watching closely is the possibility of a more organized band of showers and/or surface low pressure center passing by Monday morning/midday.  THAT is the one thing that can drag the snow level lower in this pattern, and has in the past.  The GFS depiction of snowfall pretty much agrees with my general this assessment, showing any real snow staying out of the lowest elevations:


Just so we’re all on the same page.  This setup with cold showers streaming onshore Sunday night through Monday is not our “big snow/ice storm” pattern.  The big snowstorm almost always happens when cold & dry air is in place (usually via cold easterly wind out of the Gorge) and THEN moisture returns overhead.

Speaking of that, it appears we go pretty much dry Tuesday and at least part of Wednesday as drier and colder Canadian air fills in from the north.  We should finally have a widespread frost and some chilly daytime highs only around 40 degrees both days.

Models are then in relatively good agreement that a strong system pushes inland later Wednesday and Wednesday night to end our little mini “cold spell”.  The ECMWF (and to a lesser extent the GFS) imply this could start as snow even in parts of the valley, and for sure in the Columbia River Gorge.  I’m feeling somewhat confident that some sort of snow/ice “event” is on the way for the Gorge later Wednesday through Thursday.  I’ll be watching this closely as well because, as mentioned above, this kind of setup (with the cold air in place) can cause quite a bit more havoc with transportation through the Gorge and possibly in the metro area.   I noticed 28 of the 51 the ECMWF ensemble members show 2″ or more snow in Portland by next Thursday, lending a bit of confidence.

By the way, don’t forget one of my favorite websites…almost always right on!

Just for the Christmas season, the blog snowflakes are turned on as well…enjoy.  The astute reader will notice the angle of the snowfall will change as you move the cursor…that’ll kill some work time for you.

Chief Meteorologist Mark Nelsen


All-Time Warmest November!

November 30, 2016

Our warm streak continues…

There are only a few hours left in the month of November and it’s going down into the record books as the warmest ever in most of the lower elevations of Western Oregon


Of course there is some urban heat island effect at PDX (mainly with overnight lows), but little or none in Salem and definitely none in Eugene.  So it’s just one more sign of our slowly warming climate.

The weirdest part of this fall is the lack of frost even in most outlying areas…Battle Ground had a frost briefly earlier this month, but nothing at Hillsboro?  Very strange.  As a result, the growing season has been the longest ever observed there, in Portland, and down in Eugene as well:


This was a function of a very early “last spring frost” in the first three locations.  Salem had a frost in March (later than elsewhere), which gave this year the 3rd longest growing season in that 123 year record.

It’s pretty obvious that we should all have some sort of frost/freeze by next Tuesday/Wednesday mornings.  More on that on a later post.

Chief Meteorologist Mark Nelsen

Snow Coming To The Lowlands?

November 28, 2016

7pm Monday…

What a snowstorm in the Cascades!  The past 24 hours we’ve seen more than with any other storm so far this “winter”…


For the first time since 2011 we’ve seen a general opening of terrain at Timberline and Meadows ski areas in the month of November


In one of two of these past few years we’ve seen warm rain obliterate part of the snow pack in November.  But this year I don’t see that.  This snow is here to stay; I see no period of warm rain in the next week or so.

That said, temperatures in the lowlands will be near or slightly above normal for the next 5-6 days.  Tuesday and Thursday look dry.


Is your favorite weather app showing snow or a snow/rain mix for next week?  Mine does…this is what it’s showing right now:


It says highs in the upper 30s next Tuesday and Wednesday with snow showers.  Even though that’s not in the range of our 7 day forecast, I figure I should address it if you’re seeing it right?

About 3 days ago some models (not all) were showing a big “arctic blast” coming up next week with a good possibility of snow in the lowlands.  For comparison, we have not seen arctic air move into Oregon since February 2014.  We’ve gone two winters without a deep freeze.  So of course that would be a big event.

But in the past 2 days models have backed off and (as of this evening) now show a typical “it might snow down to 1,000 ft” type event early-mid next week.

To summarize what we DO know

  1. The next 6 days will be very mild…some light rain at times
  2. A sharp drop in snow level comes Sunday or Sunday night, at that point snow may fall down into the foothills (1,500′).
  3. Next week will definitely be colder…it’s going to feel like December
  4. All areas should finally get a long overdue frost
  5. There is no sign of a big arctic blast for now

What we DON’T know yet since it’s still 7-9 days away

  1. If sticking snow will fall below 1,000’…it may or may not
  2. If it’s just a few days or a cold period that’s going to stick around for a week or more.


For the hardcore weather geeks…

The ensemble charts from both the 12z GFS and ECMWF sure don’t show a big arctic event like a few days ago (click for full view)


…but they clearly show a good agreement with 850mb temps dropping down into the -5 to -7 range next Tuesday/Wednesday.  That’s hilltop snow material (assuming there is moisture around) but tough to get snow down into the city at that temp unless we lose the mixing wind that is often present.  Some versions of some of the models (primarily ECMWF) have shown offshore flow and quite cold temps the latter half of next week, similar to what we saw around the New Year last winter.  That would be interesting because it could lead to some sort of overrunning moisture event following the cold.  Lots of possibilities ahead!

The surface temps (which in winter sometimes run too cold) from the 12z ECMWF ensembles show the cool spell next week, then warming beyond:


The GEFS ensembles from the 18z run show that cold period next week as well with highs staying in the low-mid 40s (or colder if a day were to be cloudy/wet/white).


So stay tuned, as of now there’s no sign of a December 2009 freeze or December 2008 freeze & snowstorm.  But as I mentioned in last night’s posting…that can change quickly!

Chief Meteorologist Mark Nelsen


Heavy Cascade Snow Finally Arrives Tonight

November 27, 2016

8pm Sunday…

The long Thanksgiving Weekend is pretty much finished.  If you are STILL at your relative’s home?  Time to go home, they are most likely tired of you by now.  Plus they wanted to make more turkey sandwiches and you are gobbling up those precious leftovers.

The weather in the lowlands turned out about as expected with the big soaker on Thursday. Almost 2″ fell (in case you were out of town and didn’t get to experience it).


Note how much wetter the past 6 days have been compared to the week leading up to it.  November’s rain total is now well above average…it has been a wet fall.  I missed it all since I drove with the family to the Reno area and back Wednesday through Saturday.  But oh that sunshine was nice!  Cold nights and comfortable afternoons.  Good enough for a Black Friday bike ride with nobody around


We also drove through a brief dust storm in progress between Lakeview and Summer Lake, plus it’s so cool to see the huge clouds of alkali dust blowing off that lake too.

Now let’s talk about that snow forecast.  Early last week we were REALLY excited as models showed several systems coming in Wednesday-Sunday to bring 3-6 feet of snow in the Cascades.  By Tuesday evening, models were slowing down the Thursday system and digging more energy south into California later Thursday and Friday.  As a result, at 10pm that night I had this forecast for Mt. Hood:


You can see I lowered the numbers…thinking 2-3′ by late Monday when everything was done.  Marja lowered the numbers even further Wednesday night.  On the forecast I made Tuesday PM, for the Thanksgiving Weekend you get a forecast of 20″ at Government Camp (lowest number) to a 33″ for higher up at Timberline and Meadows.  Ooops…that’s not what happened.

Instead THIS is what we have seen…as of midday Sunday.  Only 3″ at Govy!


It was a GREAT weekend for travelling in the mountains since very little snow fell, totally different than what we were warning about Monday and Tuesday.  But for ski areas, it was an epic forecast fail.

What Happened?  It’s relatively simple…the upper-level trough moving into the Pacific Northwest slowed down Thursday-Saturday, keeping us in warm air longer.  It also stalled the surface front Thursday over the Coast/Coast Range/Western Willamette Valley.  Very little of ANYTHING fell on Thursday in the Cascades.  To the south they had more action than expected (as of Monday/Tuesday) in California.  Instead of several waves of moisture moving in from the west Thursday-Saturday, half the time the moisture was coming up from the south or southwest…hardly good for Cascade snow.  This illustrates why it is important to “stay on top of the latest forecast”.  I know it’s a cliche, but it’s true.  If you saw the forecast on Monday for many feet of snow, then didn’t pay attention to the gradually evolving forecast in the days following, you missed out.  I think by 10pm Wednesday our forecast was down to 1-3 feet of snow…a bit closer to reality in the end.

What you really want for big snow in the Cascades is strong westerly or northwesterly wind to ram into the mountains.  That is happening tonight.  So tonight is the big snow dump.


I will be surprised if 10-12″ fresh snow is not on the ground at Government Camp by Tuesday morning.  15-20″ is more likely at Timberline and Mt. Hood Meadows.

Looking ahead…the weather this week looks quite benign.  Another weak system, but with that perfect northwest flow behind it, arrives Tuesday night.  That will bring another nice round of snow to the Cascades.  I expect mainly dry conditions Thursday and Friday as an upper-level ridge develops over the West Coast.

Temperatures remain near or just a bit above normal for the next 7 days.  December begins uneventfully.  But so did 2008, then we had our biggest snowstorm in 30 years just 2 weeks later!

Chief Meteorologist Mark Nelsen


Thanksgiving Travel Update

November 22, 2016

10pm Tuesday…

A wet weather pattern has returned to the Pacific Northwest.  We’ve made a few (minor) changes to the forecast this evening.  Primarily to lower snow totals for the next 5 days


  • Showery conditions tomorrow (Wednesday), but not stormy.  The usual stuff
  • Thanksgiving Day will be VERY wet west of the Cascades.  Expect slow highways and freeways
  • Snow falls in the Cascades the next 5 days.  Heaviest snow will be on Thanksgiving Day.  But the snow level may briefly lift above the passes on that day
  • Friday now looks drier (or even mostly dry!) as a weather system stalls offshore before moving inland Saturday
  • I’ve lowered the total snow expected the next 7 days due to the drier Friday and more snow staying above the passes.



Don’t even worry about anything west or north of the metro area.  Forget about the Gorge too


A surface low pressure system will pass by Thanksgiving evening just offshore.  The pressure pattern isn’t right for a big wind event in the valleys, but gusts 25-35 mph are likely.

As of now, Mt. Hood Meadows, Timberline, & Mt. Bachelor plan to open at least a few lifts Friday.  With more splitting and energy headed south showing up on models , it might be tough to get too much terrain open if we don’t get at least 18 inches up there.

I’ll be driving about 9 hours on Wednesday…at least it’ll be a nice day to see all the wonders of Eastern Oregon and NE California on the way to Reno.

No posts until Sunday when I’ll be back at work.  Drive carefully everyone.


Chief Meteorologist Mark Nelsen

Thanksgiving Travel: Could Be Rough For Some

November 20, 2016

After several years of uneventful Thanksgiving road conditions across the region, this year is looking much different.  If you are headed into mountains either east, west, or south, pay attention to the forecast this week.

What’s going on?

As of this Sunday evening it appears 3 separate weather systems will move through the region Tuesday through Friday.  In between each and after Friday’s system more cold showers will be streaming onshore.  Those showers turn into snow in the Cascade & higher Coast Range.  The Blue Mountains will get in on the action at times in NE Oregon too.  The Siskiyous could really get slammed later this week as well.  The one place you DON’T need to worry about is the Columbia River Gorge.

Snow levels will be fluctuating between 2,000 and 4,000′ Tuesday through Sunday since these are “cold” storms, totally different from the warmer events we’ve seen so far this season.  Basically this IS the beginning of our winter season here in the Pacific Northwest.

We don’t need to worry about flooding because of snow falling in the mountains instead of rain, and it’s not the incredibly heavy subtropical rain we saw in October.  Check out the WRF-GFS precipitation forecast from Monday through Thursday afternoon…a solid 1.5″ in the valleys and 2-4″ in Cascades and Coast Range:


Then from Thursday PM through Sunday PM the rain lightens up in the valleys a bit.  Maybe 1″ or so, but another 2-4″ in the Cascades and Coast Range.  During this period it is ALL SNOW above about 4,000′!


My forecast for the Mt. Hood area says the ski season starts big-time this coming weekend!



Yes, you are reading that correctly…several feet of snow are coming.  That includes down to Skibowl & Hoodoo ski areas as well.  In the past 4 years there hasn’t been more than 12″ of snow on the ground at Government Camp on any November day.  Looks like we’re going to see much more than that one week from today!

Here is a detailed look at what you can expect on all the major highways heading away from the metro area:




Chief Meteorologist Mark Nelsen

Ski Season Could Start Thanksgiving Weekend

November 17, 2016

9pm Thursday…

The past 4 Novembers have been a real disappointment for skiing with either mild temps or snow getting washed away by rain right after it falls.  This 2nd half of November 2016 looks different.  Models are in pretty good agreement that we have a series of “cold” and wet storms that will move through the Pacific Northwest starting next Wednesday.   Snow levels vary between 3,000 and 5,000′ next weekend.  You can see the cool westerly flow on the ECMWF for Thanksgiving Day:


and the ECMWF ensembles from last night’s 46 day run show cooler than normal temps for the next two weeks.  This is the 850mb temperature anomaly:



Check out below normal 500mb heights the next two weeks as well:



How much snow?  To start, here’s the GFS 10 day rain forecast showing 3-5″ in the valleys, a bit wetter than normal and definitely wetter than what we’ve seen so far this month:


Convert that to snow and you get a solid 3-4 feet between now and the Sunday ending Thanksgiving Weekend!


Now that would open up all the ski resorts wouldn’t it?  Even half of that would get things halfway open.  By the way, the ECMWF (more reliable model) has similar totals for both rain and snow.

So…get the skis/snowboards waxed…things are definitely looking up!

For the real weather geeks of course you know the ECMWF monthly run goes out two more weeks.  But since last winter I’ve generally not shared those images since the usefulness drops off beyond about two weeks.  For fun though here you go:



Definitely drier week 3 with heights going above normal, then average after that.  Again, not real useful is it?

Chief Meteorologist Mark Nelsen