A Winter Wonderland New Year’s Morning? Mainly In The Hills

December 31, 2016

11am Saturday…

As mentioned in the previous posting, a very weak weather system moves over the Pacific Northwest tonight and New Year’s morning.  During much of the system’s passage, temperatures will be too warm at the lowest elevations for snow to stick.  But near the end, as showers are tapering off, snow may stick in spots all the way down to the valley floor.


  • Your New Year’s Eve plans are safe  There won’t be any snow on roads in the lowlands through at least 2-3am.
  • But any of us could see snow mixed in with the rain during the overnight hours.
  • Near/above 1,000′ (top of the West Hills), some accumulation is possible, but even then it may be a degree or two too warm for sticking snow.
  • 4am-10am a dusting to 1/2″ is possible anywhere, but I’d lean towards a dusting and not that half inch.  Many of us get nothing tomorrow morning.
  • The rest of tomorrow we’ll be above freezing, at least through 3pm, so I think roads will be clear.
  • An arctic front passes through the area tomorrow evening; that means a sudden arrival of cold east wind and all wet areas will freeze.  At that time we’ll be dry, or just a few flurries maybe.


  • Rain or rain/snow showers change to mainly snow showers above 500′ by midnight.  At that time some roads will start getting snow-covered above 1,000′.
  • Anytime after midnight and through Sunday any road in the Coast Range and above 500-1,000′ west slopes of the Cascades could get snow-covered.  That includes Sandy, Estacada, Beavercreek, Mill City etc…
  • Expect 1-3″ in these areas, more above 1,500′.


The NWS is going for a Portland snowstorm tonight and Sunday morning, but I think it’s unlikely.  They are forecasting 1-3″ in the metro area (3″ on hills) and have a winter weather advisory up starting at 10pm.

I feel that’s way overdone for several reasons.  The biggest is that we’re in mild onshore flow through around sunrise Sunday.  In fact southwest wind picks up this evening and continues until almost day break.  Freezing levels are above 1,000′ through 7am tomorrow, when almost all of the moisture will be falling out of the sky.  I’ve seen this many times here in Portland.  We’ll be too warm down at the valley floor until sometime after 4am to even think about snow sticking down here.  There is excellent model agreement on this as well.  That southwesterly breeze is a real killer (for snow) UNLESS the atmosphere is colder than what we’re expecting now.   Take a look at model snow forecasts from the ECMWF, WRF-GFS, & RPM and they agree.  Note the RPM snow is mainly after 4am:

rpm_4amsnow1km ecmwf_snow_18z rpm_snow_12z-1


None of those inspire a lot of confidence for a sledding day Sunday in Portland do they?

Now during the day on Sunday cooler air gradually filters in from the north, but we’ll be battling daytime heating (a little) too.  Leftover snow showers could dump a dusting anywhere during the day, but most areas will be slightly too warm still for stickage.  So we should stay above freezing through 3pm, then we plunge into a frozen abyss.  Okay, that’s a bit dramatic, but I don’t know when we’ll go above freezing again…maybe about 6 days from now?  We’ll see about that.

To wrap it up, I think many of us will wake up to a white dusting, but a frozen city with snow all over the roads like we had with the big fiasco in mid-December is unlikely.

Happy New Year!

Chief Meteorologist Mark Nelsen






Arctic Blast Next Week

December 29, 2016

11pm Thursday…

Models are in very good agreement now that we’re about to experience our first “arctic blast” across the Pacific Northwest in 3 years.  It arrives Sunday night on northerly winds pushing out of Canada and continues the entire rest of the work week.  After Monday we go into a gusty east wind pattern with bitterly cold air moving through the Columbia River Gorge and into the Portland metro area.  Those waterfalls are going to be looking great by midweek all frozen up!

First, will we get snow Saturday night or early New Year’s morning?  I think anything other than flurries or a dusting is quite unlikely.  The showers are pretty much gone by the time the snow level lowers down into the lowlands.  In fact after 7am Sunday we’ll probably be dry.  Take a look at 5 different model forecast of precipitation after 4am Sunday, then the snow that could produce.  Yeah, looks pretty dry:


The ECMWF and WRF-GFS model snowfall forecast don’t inspire much confidence for sledding in the lowlands Sunday either.  Click for a closer view:

After Sunday that cold air takes over and we’re likely going to be sunny and dry most or all of the work week.  Take a look at the WRF-GFS cross-section:


Time goes from RIGHT to LEFT.  The right side is Monday morning, left side is next Friday morning.  Clear areas are less than 70% relative humidity…that’s a very dry atmosphere.  The wind barbs are easterly the entire time.  Through Wednesday morning the northeast/east flow extends all the way up to 10,000′.  This is a rare “deep” arctic airmass.  That means unusually cold temps in the mountains too.  Probably only 0-8 degrees at the ski areas Monday!  Northeast wind will be widespread across the region Monday/Tuesday.  After Wednesday it becomes more of an east wind through the Gorge but light wind elsewhere.  That calm wind will allow for very cold nights…5-15 degrees west of the Cascades.

Beyond our 7 day forecast there are hints of moisture returning next Friday, or Saturday, or Sunday, depending on which run of which model you are looking at.  This is the graphic I used for the 12 Day Trend I used this evening at 10pm.  I do this most nights to give viewers a GENERAL idea of what we’re seeing beyond the next 7 days.  It’s very useful in situations like this.  I think there’s a decent chance of getting some sort of snow west of the Cascades between days 8-12.  But it’s unknown at this point if we have a major ice/snow event coming sometime NEXT weekend or beyond.


The cool pattern is going to continue.!

It’s my weekend the next two days but I’ll be back at Sunday.

Have a safe and Happy New Year!

Chief Meteorologist Mark Nelsen

Drier Than Normal Next 7 Days, But Turning COLD!

December 28, 2016

6pm Wednesday…

Today was an amazingly boring weather day, with just areas of low clouds/fog in the valley and some sunshine central/east metro area.  Not much happens tonight, Thursday, Friday, or the 1st half of Saturday.  Take a look at the 3 day rain forecast from our RPM:


Yes, pretty light stuff with a weak cold front that comes through Thursday night.  That means the daylight hours tomorrow and Friday should be dry.  Saturday morning will be frosty and cold with temps below freezing under a cool airmass.

Things start to get interesting just about the time all you folks start partying New Year’s Eve (2nd half of Saturday).  The upper-level flow begins coming in from the north, and a disturbance is dropping south through British Columbia.  Take a look at the 500mb chart for 4am Sunday:


You see the disturbance carving out an upper-level trough right over us.  Air is flowing from the arctic south straight into the Pacific Northwest.  At the surface, there is a surface low pressure area developing over southern British Columbia.  This map is right at 1am…one hour into the New Year.  Note two things:  first, the airmass is quite chilly, snow could fall even below 1,000′ in this pattern.  The 2nd, a tremendous westerly to southwesterly flow is on west of the Cascades due to that developing low.  That gusty mixing wind will likely keep sticking snow above 1,000′.


There will be plenty of showers, with the ECMWF showing the potential for 8-15″ snow in the Cascades, that’s due to a very strong westerly wind between 2,000-6,000′.  Perfect for orographic lift…the west slopes of the Cascades will get pounding by heavy precipitation for about 12 hours from late Saturday through late morning Sunday.


By 7pm Sunday the surface low pressure center is weakening and dropping south over Western Oregon.  At this time the surface wind is turning north and northeast as very cold (and very dry!) arctic air invades the Pacific Northwest:


The WRF-GFS is even more interesting, check out the 24 hour snow total ending Sunday PM:


Notice how far west the snow is pushed down into the foothills and even far eastern Willamette Valley!  That’s due to the strong westerly flow pushing up against the west slopes of the Cascades.  It’s only noticeable if you regularly look at these maps.  This says significant snow could fall even down to or below 1,000′ on the east side of the Willamette Valley.  For sure the hills will get a dusting, but in this pattern I think significant snow down on the valley floor is unlikely.  But if you live in Sandy, Estacada, Sublimity, Mill City, Sweet Home etc…?  You could see a few inches of snow on the ground by Sunday AM or midday.  After that ALL models agree we dry out quickly as a the dry arctic airmass moves in.

To summarize:

  1. A significant snowfall is unlikely in the western valleys and Portland metro area New Year’s Eve & Day
  2. But we could see a dusting of snow just about anywhere early New Year’s Day, most likely that’ll happen on the hills
  3. Roads may get covered with snow above 500′ or so near/in the Cascade Foothills by New Year’s Morning.
  4. Coast Range roads will likely be snowy/icy later Saturday night through Sunday.
  5. There is relatively good model agreement on the general progress of these weather events Saturday/Sunday

Beyond Sunday…

Models are in excellent agreement that we’re into a cold and dry pattern for at least 3 days…Monday/Tuesday/Wednesday.  How cold?  Now at least the GFS has come around to the colder ECMWF/GEM models, showing 850mb temps dropping down to the -12 to -13 range Monday night and Tuesday with offshore easterly flow.  These numbers are in the same category as the December 2009 and December 2013 cold spells.  Not a massive 1990-style “Mr. Cold Miser Has Arrived” blast, but definitely an outbreak of arctic air.  So prepare for the coldest airmass we’ve seen in 3 years.  It’s going to be in place over us much of next week.  That means wrap pipes and protect your pets/livestock/animals.  High temps will likely only get up to around 30 degrees even with full sunshine.  That’s assuming we get little/no snow cover on the ground.  If some part of the Willamette Valley ends up with 2″ or so (not expected for now), temperatures would be a good 5+ degrees colder.  East wind will also be blowing through the Gorge, although it doesn’t appear to be a real strong wind for now.  Lows should reach down into the 10-15 degree range, even here in Portland.  It’s about time!

Our forecast looks like this for lows:


Note the lowest temperature we’ve seen each winter from my OMSI presentation back in October.  During the last December arctic blast we saw a few upper single digits in the metro area and then lower teens.  That’s why I have that 12 degree forecast, especially with the east wind not looking too strong.


There is very good agreement on this second part of the forecast this next week…the cold part.  Check out the ECMWF ensemble chart from this morning:


Look at all those lines very close together through next Thursday, the 5th.  Then things break down, but the trend is to add some moisture back into the forecast as the pattern stays cold.  Yes, we could be looking at some sort of snow/ice event the end of next week.  That’s still 8-10 days away though…

Chief Meteorologist Mark Nelsen




2017: First Week Looks Cold

December 26, 2016

9:30pm Monday…

The astute FOX12 viewer will notice a sudden drop in the high temperature Monday…the 2nd of January.   And your weather app is looking quite chilly for next week too isn’t it?   Well it’s looking like we’re going to turn quite cold next week once again.

Models all show a similar pattern developing Sunday through sometime later next week…an upper-level ridge builds over Alaska.


That forces a cold airmass to dive down through western Canada and into the Pacific Northwest late Sunday through next week.  In general, the pattern is the same on all models.  As a result I’m quite confident we’re headed for a very cool first week of January 2017!

But will it just be cool like earlier this month?  Or could it be a real arctic blast, one we haven’t seen in 3 years (since December 2013).  That’s a good question and I don’t have an answer for you yet.

For reference, I’d consider a widespread Pacific Northwest arctic blast one in which 850mb temps drop down to at least -12 (celsius) over Portland/Salem.  The last 5 times that has happened?

December 2013:  -14
November 2010:  -12
December 2009:  -12
December 1998:  -18
December 1990:  -22 (coldest 850mb temp on Salem sounding record)

You can see a true widespread Pacific Northwest outbreak of deep arctic air is quite rare.  It’s like the weather geeks (including me) are reaching for that “big one” each winter, but most winters will end in disappointment.

It could possibly happen next week.  The ECMWF model run from this morning was that cold, but other members of its ensembles were not.  Same thing with the GFS model.   Check out the ECMWF ensemble chart from this morning:


Quite a variety of solutions by next Tuesday/Wednesday, but in general it looks cool. Check out the ensemble forecast temps from the same morning run:


A pretty clear signal for a chilly week ahead…starting Monday.  It was interesting to note that only about 1/2 of those ensemble members showed 2″ or more snow over Portland in the next 8 days, but that number jumped to 46 of 51 members by the 12th day.  The point is that once real cold weather arrives, moisture will likely interact with it at some point.  Especially since the pattern seems to stay cold for a while.  Look at the 1st and 2nd week of last night’s ECMWF monthly run.




That’s a cold pattern with the upper-high remaining over Alaska and downstream troughing over us.

This evening’s GFS run is not nearly as cold as the ECMWF for next week; it looks more like what we saw earlier in December.  But I’m sure there will be lots of twists and turns the next few days on the models.

Stay tuned..

Chief Meteorologist Mark Nelsen

Major Snow Storm In Cascades Begins Soon

December 26, 2016

4pm Monday…

I hope you all had a Merry Christmas!  Time to get updated on the latest weather happenings.  I see I didn’t miss much here…I was in Florida Monday AM through Saturday afternoon.  The morning my family and I flew out (Monday) it was COLD sitting in the economy lot with ice pellets/snow/rain pelting us along with a breeze.  But the south wind arrived as expected and the vast majority of the metro area made a quick switch to rain.

Today we’ve got a front moving onshore with lots of precipitation.  Due to strong westerly wind up around 5,000′ following the front later tonight through Tuesday, we’ll get maximum snow enhancement along the Cascades, and Blue Mountains in NE Oregon too.

This storm is going to be a major snow storm up in the Cascades:


What timing too…1.5 to 2+ feet of snow in the Cascades right during the peak of the ski season.  I’ve heard in the past that these two weeks of Christmas Break are HUGE for ski areas, accounting for a large part of their winter income.  So the good times with Ski Season 2015-16 will continue!

Also note the heavy snow for the Blues and Wallowas, mainly during the daytime Tuesday:


Eastern Oregon has been extremely cold this December.  In fact as of today it’s the 2nd coldest December on record in the Baker Valley (Baker City/Haines/North Powder).


The presence of snow cover allows any clear night to turn frigid.  Plus we’ve seen a real absence of moist/warm southwesterly flow to clear out the trapped low-level cold air in the Intermountain Region.  The average low at Baker City is 15 this time of year, so getting below zero IS quite cold.  This is a December to remember over there!

The cold air will stay entrenched the next 48 hours, and that means the strong south & southeast wind through the Blue Mountains will be here with this snowy system too.  The result?  Blowing and drifting snow with near-blizzard conditions again along parts of I-84 Tuesday from Emigrant Hill to Baker City.  There won’t be all that much snow in the valleys, but lots of blowing/drifting.

The storm leaves the area by Wednesday sunrise so Wednesday and Thursday look pretty tranquil across the Pacific Northwest.  A weak system will drop in over us Friday, lowering snow levels down below 2,000′ again.  There won’t be much moisture with that one though…just a few more inches in the Cascades.

What lies beyond for the first few days of 2017 sure looks interesting…more on that in a post later…

By the way, you are living through the coldest December (or any month) in 3 years here in Portland.  The average temperatures of 37.2 degrees is just slight warmer than the cold December 2013 and 2009.  Things have FINALLY gone back to normal (at least for now) after a long almost 3 year period of very warm weather.  We’ll see how long it sticks around.

One more quirky fact…December is the only winter month that has been getting COLDER over the years here in Portland.  January/February/March have definitely been going up, but December for some reason is going DOWN.  Strange eh?


Chief Meteorologist Mark Nelsen


Christmas Vacation

December 19, 2016

I’ll be on vacation the rest of this week, back at work for the 10pm show Christmas Day.   So likely no postings this week, unless something real exciting shows up on the maps.  Heading for a brief stay in a warmer place.

This isn’t the hotel I’m staying in, but hope to visit it this week!  It’s been in my bucket list for a few years.  Can anyone ID it?


Merry Christmas!

Chief Meteorologist Mark Nelsen

Brief Freezing Rain or Snow Monday AM

December 18, 2016

10pm Sunday…

Our cold spell is about to come to an abrupt end in the next 12 hours.  The lowest part of the atmosphere over the western valleys of Oregon and S.W. Washington is still quite chilly this evening with many of us below freezing.

During the night a strong southerly and/or southwesterly flow will be developing.  By 4-7am up at 2,000′ models say the southwest wind will be blowing around 30-40 mph transporting in much milder air.  That’s in advance of a relatively strong cold front approaching from the northwest.

Now typically if we have a juicy front approaching with a dry and cold airmass at the surface, it’s quite possible to get some sort of snow/ice storm.  But this time it’s much different from last week.  This system is coming in from the northwest and gusty southerly wind arrives by tomorrow morning.  The easterly Gorge wind that would often transport very cold and dry air into the Portland metro area has died down to just an easterly breeze that is barely making it out of the Gorge.  I was just at a house about 200′ above the Columbia River in Corbett and I can vouch that it IS just a breeze at this point.  So the “freezer door” is now shut and the atmosphere will quickly moisten and go above freezing overhead by 4-7am.

At the same time precipitation will be arriving.  Between 4-7am SOMETHING frozen will likely fall for many of us.  There could be spots of snow from the metro area north but I think it’s more likely we’ll get areas of freezing rain for a couple of hours at the beginning of the Monday AM commute.  In this case it can’t last long with the mixing southwest wind arriving both above and the Gorge wind nearly dead.  So the main message is:  Be very careful if you are out and about between 4-7am; what appears to be rain may be freezing on the roadways in some spots.  Or there could be light snow accumulation at first as well.  You can see the 4-7am precip forecast from the WRF-GFS this evening:


IF that were all snow, that would imply an inch or so accumulation.  But I think freezing rain is more likely for the spots that remain below freezing since the airmass above appears to be mainly too warm for snow (for most of us).  Check out the snow forecast from our RPM model, which implies at least a dusting for many of us before the changeover to regular rain:


And the WRF, which holds the snow in the higher elevations only:


Beyond 7am temperatures should warm above freezing quickly.  In fact by tomorrow night at this time we’ll be around 50 degrees with a gusty south wind!  It’ll feel “tropical” after the last couple of weeks…

For you folks in the (central/eastern) Gorge, you’ll likely get a mix of freezing rain/snow through tomorrow evening before a changeover to rain tomorrow night.  A gusty WEST wind there by Tuesday means high temps in Hood River and The Dalles will surge well into the 40s…the melt will be on!

Chief Meteorologist Mark Nelsen