Rare “December Drought” & LOTS of Chilly East Wind On The Way

December 3, 2017

7pm Sunday

We’re drying out this evening and now you can say GOODBYE to the rain for quite a while.  Meteorological Winter (December-February) is going to start out very dry.  It’s possible we won’t see any significant rain for more than 10 days!

The typical westerly jet stream (our storm machine) we see in winter is heading much farther north this week and beyond.  A strong upper-level ridge of high pressure is developing along the west coast of North America and it’s going to stick around for an unusually long period of time.    You can see on the forecast chart from the ECMWF model for this coming Wednesday:

The lines are the actual model ensemble average (51 different runs of the same model) and the colors represent deviation from normal for this time of year.  Huge above average heights all along the West Coast, and well below normal in the Eastern USA.  Then let’s move ahead to ONE WEEK LATER…same thing!  If this pans out, expect dry conditions all across the far western USA for the next 10 days.  All models are in good agreement with this scenario as well.

Looking farther ahead, here’s the view at Day #15, Monday the 18th.

This is the beginning of the first week of Christmas Vacation for lots of kids (some like mine don’t start that 1st week until Friday the 22nd).  The ridge is still there, but a bit weaker, and more likely we’d see some mild westerly flow breaking through at times.  All global models show this same scenario through the next two weeks.  Either a dry & warm upper-level ridge over us or wet at times & warm (this last map).  NONE show a cold and wet or cold and dry pattern in the mountains.  Let’s cover the main effects from this upcoming weather pattern:



Notice I said it’s a warm UPPER-LEVEL ridge.  At our latitude in winter when it warms up overhead with strong high pressure, it won’t be warm down in the valleys where most of us live.  A strong inversion will form under the warm air in the mountains; that starts Tuesday.  That’s because the long nights and very weak daytime sunshine doesn’t allow the surface layer of cold nighttime air to warm up.  Assuming these stagnant conditions continue, it will actually cool a bit over a period of days or a week.  That’s why you’ll notice my current 7 Day forecast is warmest on Tuesday (when the first east wind arrives), then turns cooler later this week and into next weekend.  East of the Cascades a cool pool of air will form below about 3-4,000′ in the Columbia Basin.  That pool of cold air is heavy and dense.  It’ll be trapped over there except for one spot it can move at sea-level…through the Columbia River Gorge.  Yes, we have unending days of…


It’s time!  Every winter those of you at the west end of the Gorge and east Portland metro area suffer through long periods of cold east wind.  That begins Tuesday afternoon and continues until further notice.  I can’t tell you when it will stop this time around…sometime the following week maybe?  At first you can expect temperatures in the 40s out there (Tuesday), but then as the cold air gets established east of the Cascades the airmass will cool.  By next weekend you’ll be only in the 30s with east wind gusts in the 60-80 mph range anytime beyond Wednesday.  It’s going to be a long haul folks!  Tie everything down.  Rumor says Wednesday could be a “Vista House Day” for the weather geeks.  But…there is one huge benefit to that dry east wind…


Yep, we’ve got day after day of sunshine coming.  In the metro area we’ll start with areas of fog Tuesday, but Wednesday and beyond it’ll be too dry to support fog for us.  This is the cool/crisp weather I personally prefer in December IF we can’t get any good storms.  If you live from Salem south in the valley it’s possible your fog lingers all day Tuesday and part of the day Wednesday, it depends on how much drier air works into the valley midweek.


I don’t think you need to do it although why not do it now for the season and be done with it?  In calm areas this week I could see low temperatures drop into the 22-26 degree range (after Wednesday).  Windy areas may not drop to freezing at all.  Those temperatures generally aren’t cold enough to cause big issues, but again, you could just get it done for the season.


We are very lucky some snow showed up this week, because I don’t see a pattern that brings snow to the ski resorts in the next 10 days.  Timberline & Meadows are open, with 2.5-3 foot bases.  Good enough with modern grooming techniques and short sunny days around 45-55 degrees won’t melt much but that snowpack will become a little…er…consolidated (an icy brick).  Again, groomed runs should be just fine though.   Hoodoo, Skibowl, & Willamette Pass all need more snow to open.  Hopefully some surprise can show up near the start of Christmas Break.

Is this a rare event?  Yes and no.  I’ve gone back and looked over the records.  Let’s assume we go 10 days without rain (a relatively big assumption at this point).  That has only happened in 7 Decembers out of around 80 years of records at PDX.  We had 11 consecutive dry days in 2009, and 14 in 2005 and 12 in 1989.  All 3 were followed by great skiing the 2nd part of winter.  It also happened in 1993 and 1980, those two weren’t very good snow seasons in the Cascades.

Enjoy the next week!  Chief Meteorologist Mark Nelsen


Fresh Mountain Snow and a Very Dry December Start

November 30, 2017

10pm Thursday

Today was a gray day but only around .10″ fell in much of the metro area…a classic “soggy” but not “soaking” Pacific Northwest day.  The month ends in just two hours;  it was a slightly wetter than average November in Portland.

Mark November Rain

The first day of December (tomorrow) looks dry as we wait for a weakening cold front to move inland during the evening.  Another chance to hang your Christmas lights and stay dry.   For you skiers/snowboarders this is the plan for tomorrow and the weekend:

Snow Report2

There is only one wet day in our 7 Day Forecast this evening and that would be Saturday.  That’s because next week a new weather pattern takes hold.  It’s a pattern we never saw last winter;  a big “blocking” ridge of high pressure parked over the west coast of North America for many days, possibly well beyond a week.  For comparison, the last time we saw 7 consecutive dry days in December was 4 years ago.  Back in December 2011 we went 9 consecutive days without rain so it’s a rare event but it DOES happen.  Take a look at the upper-level map (500 millibars) for Tuesday.


You see the big ridge developing along the West Coast and a very cold trough pushing cold air down over the Great Lakes.  Next week I’m sure the national weather story will be winter arriving in the eastern half of the country.

In this pattern we’ll see surface high pressure set up east of the Cascades.  That will push a strong easterly wind through the Columbia River Gorge.  Tuesday is the beginning of that setup and it’s possible that east wind will continue for at least week!  In December an east wind is cold as the valleys cool off and stay chilly under wintertime inversions.  The Cascades will turn quite warm next week, likely well into the 40s or even 50s at the ski resorts.  But blue sky and clear/cold nights will keep snow melt to a minimum.

That upper-level ridge sticks around on ALL models through the next two weeks.  Check out the GEM (Canadian) ensemble average for Thursday the 14th:


and the ECMWF ensembles…similar setup with a cold eastern US and mild west (above the inversions):


On a side note, are you are headed out to a tree farm this weekend?  Then Sunday is your day.  It should be mainly (or all) dry.  Saturday looks like a soaker.

Mark Christmas Tree Forecast

Chief Meteorologist Mark Nelsen

No Frost Yet In Portland

November 28, 2017

7pm Tuesday

If you are a gardener like me there’s a decent chance you are staring out the window at a relatively green garden as we head toward December 1st.  I have only had a low temperature of 30 degrees at my home and the banana trees barely look touched by frost and the annuals are rotting, but still alive due to no significant freezing action.  See the lows so far this fall around the metro area.

Mark Low So Far This Winter

The temperature needs to drop down into the upper 20s to really kill off many annuals and very few of us have seen that.  Not on the map is downtown Portland which has only seen a 37 degree temperature.  This is a bit late, but not too unusual.

Mark First Frost Last Few Years

And having a first frost in early December sure is not indicative of the winter to come.  Last year it didn’t happen until December 6th and we know how winter (brrr!) turned out.  It’s more an indication of the weather pattern from Halloween into December.  For frost we need clear nights and a relatively dry airmass to allow temps to drop.  When we have constant rain that doesn’t happen.

But fear not, I expect frost for almost all of us at some point next week.  An east wind pattern is coming much of next week (after Monday).  The result should be widespread freezing for just about all of us west of the Cascades.  Dry offshore flow in December means fog and/or frost west of the Cascades.  It’s likely downtown Portland and a few windy spots in the western Gorge still won’t drop to freezing.

Speaking of dry, the big change is still on for next week.  Bad news for ski areas that are only going to pick up a maximum of 2 feet new snow the next few days, then dry out.

Snow MtHood Outlook

But it’s good news in the lowlands, a chance to hang your Christmas Lights and not get soaked maybe?

Chief Meteorologist Mark Nelsen



Mainly Calm Weather Heading into December

November 26, 2017

9pm Sunday

Thanksgiving Weekend is wrapping up now with lots of you at home relaxing, getting ready to head back to work tomorrow.   I had some leftovers here at work…very nice.

Last week was quite warm, which cancelled out the cold first half of the month.  You can see the Pacific Northwest is running about average temp-wise so far this month.  The nation as a whole has been warmer than average:

Skiing has been shutdown on Mt. Hood now due to the washout through Thanksgiving Day.  Timberline just announced they won’t open again until Friday and Meadows/Skibowl are on hold as well, waiting for more snow this week.  The good news is that there IS some snow coming for the Cascades this week, 2-3″ fell this evening, and another 10-20″ is likely by next Sunday.  Here’s the ECMWF snowfall forecast:

Along with the 12-20″ (very dense & solid) base already on the ground that should allow some basic ski runs to open next weekend at both Timberline and Meadows.  Skibowl might be tougher since some of the snow falling this week won’t get below 5,000’…we’ll see.

In the lowlands it’s been a wet November once again but not crazy “flooding wet”.  In general it hasn’t been stormy this month like we sometimes see.

The rain this week should be relatively light.  I see one weak cold front coming through Tuesday, then another on Thursday afternoon/evening.  Other than leftover showers Friday and Saturday, that’s it for the next 7-10 days.   In fact the Friday/Saturday showers aren’t more than just showers because the main energy with that cold system dives south into California instead of heading into the Pacific Northwest.

If I don’t sound real enthused about the upcoming weather it’s because I’m not.  The pattern over the next 10+ days signals a very slow start to “meteorological winter” which begins on December 1st.    There DOES appear to be a change in the pattern about 8-10 days out.  A strong upper-level ridge builds right over us or just to the west, blocking storms and giving us mainly dry weather for NEXT week.  For now there is excellent agreement on this basic feature…look at the forecast GEM, & ECMWF ensemble averages of 500 millibar height 10 days from now…on Wednesday the 6th.


Then the GFS & ECMWF 5 days later…this is two weeks away…

They all look the same!  That’s some unusual model agreement that about 8 days from now the pattern will change.  It’ll feature an upper level ridge in the West (dry & mild) and cold troughing in the Eastern USA.  This is more likely a chilly east wind pattern for us, depending on the orientation of the upper-level ridge.   I will mention this in the 12 Day Trend…a graphic I use from time to time in the 2nd half of the 10pm show.


By the way, note this isn’t a 12 day FORECAST, but a general trend.  In fact I’d rather not have those “40s” on there or specific clouds for each day, so don’t read too much into that.  I like the text part best.

Regardless, it’s obvious the early part of December will not feature much active weather.  Weather Geeks:  Get your Christmas shopping and chores done now…who knows what is around the corner in mid/late December!  As I recall some seasons that started out slow suddenly saw the weather action pick up after early December (2008).  I think 2007 was pretty quiet too early on, followed by tons of foothill snow.

Chief Meteorologist Mark Nelsen



Happy Thanksgiving! Good Travel Weather in PACNW

November 22, 2017

9pm Wednesday

It’s Thanksgiving Eve and all is well on the weather front.  It’s been a record warm day all across the region.  Here at Portland we’ve only hit 56 degrees as of 9pm with a persistent “cool” easterly breeze out of the Gorge.  But we have until midnight and warm southerly wind is quite close.  So it’s quite possible we still break the 59 degree record before the day is finished.

The very warm and moist sub-tropical airmass gave us some river fog in some places.   That humid air gets cooled by the chilly 50 degree water.  When that happens the air can’t hold any more moisture so the water vapor condenses into those little fog droplets…fog hangs low over the river.  Makes for a nice pic!  Thanks to Tim Mulshine for this one.


Records have been tied or broken at Hillsboro, Astoria, McMinnville, Roseburg & Medford.  That’s just in Oregon.  Seattle made it to 68, blowing away the old record by 10 degrees!

Record Highs Cities

Tonight will be one of the warmest November nights you have ever felt in our area, crack open the windows and bring in some fresh air while you sleep!  With an approaching cold front I expect southerly wind to pick up in most areas except IN the Gorge.  That keeps most of us right around 60 degrees right through around noon on Thanksgiving Day.  Cooler air pouring in behind the cold front means dropping temperatures after noon-1pm tomorrow.

Other than lots of showers, mainly the first half of the day, it appears there won’t be any significant weather on Thanksgiving Day.  Same thing for Friday and Saturday.  Friday looks mainly dry, then a warm front with the usual solid gray sky and light rain comes in Saturday.

I have the next two days off (along with Saturday), then coming in on Sunday I’ll take a look at the big picture; by that time the 7 Day forecast will include December already…time is flying!

Mark Thanksgiving Day Fcst



Will 4 Days of Warm Rain End An Early Ski Season?

November 19, 2017

9pm Sunday

November has been near to slightly below normal temperature-wise across much of the West.

Compare that with the blowtorch November last year across the entire USA!

Along with near normal rainfall that has given us a very nice mountain snowpack already.  At the Mt. Hood Test Site at the lower part of Timberline Ski Area, 34 inches of snow sit on the ground, containing 7.80″ snow water equivalent.  That means if you could melt it with a snap of your fingers, it would be just like 7.80″ of rain fell suddenly.  See how this compares to the past 8 Novembers at that site.

Pretty nice eh?  Quite a change from the past 3 mid-Novembers with very little snow on the ground at this moment.

That was the good news.  The bad news?  We have 4 days of warm rain (Monday-Thanksgiving Day) headed for all elevations in the Cascades.

The result will be substantial snowmelt.

But I do NOT believe this is the end of our early ski season.   There is no reason to panic when you hear many inches of rain are coming to your favorite ski resort.

It’ll be a setback, but this was an early bonus anyway.  A good part of the current snowpack will survive, in fact in the past 20 years we haven’t made it to 30″+ snow depth at this location followed by a complete melt down.  Sometimes it has dropped quite a bit (like the week ahead), but then more snow fell within a week or two.  If you are a skier or ski resort manager there’s no reason to freak out.

The pattern for the next 4 days looks like this…

a big ridge of high pressure with very warm temperatures overhead.  Lots of subtropical moisture will be streaming north around this ridge, pushing sticking snow levels up around 8-10,000′ on Mt. Hood.  We’ll be breaking out of the usual November inversion when we get a southerly wind so we can also expect a very warm Thanksgiving Week in the lowlands.  A record high is possible in Portland either Tuesday or Wednesday (records are 62 & 59 for those dates).

I expect lots of rain, but this isn’t generally a flooding rain pattern with the flow coming steeply from the southwest (instead of west).  Plus no one system seems to sit right over us for an extended period of rain.

There is one huge bonus…THANKSGIVING TRAVEL THROUGHOUT THE PACIFIC NORTHWEST SHOULD BE EXCELLENT.  There will be no snow over mountain passes anywhere in Oregon or most of Washington from tomorrow morning through Thanksgiving Day.  Even after that time through Sunday sticking snow levels seem to remain mainly above the Cascade Passes.

So enjoy the week ahead…at least you’ll save on your heating bills!

Chief Meteorologist Mark Nelsen

Winter is Here, And Not Just In The Mountains

November 15, 2017

9:30pm Wednesday

Heavy snow is falling in the mountains tonight.  The nice folks at Skibowl installed a very bright yard light this fall, so now we can see what it looks like after dark (until night skiing starts in December).  It’s been like a big “snow-globe” on the big monitor overhead here in the weather center.  This is great news; two more local ski resorts will be opening this weekend:

The cool westerly flow of showers will continue through early Friday, dumping 1 to 2 feet of fresh powder

Of course that means rough driving over the Cascades tomorrow and Friday.  Things should improve over the weekend with Saturday sunshine and then a warmer system the 2nd half of Sunday.   But the message is clear:  WINTER HAS ARRIVED AND IS HERE TO STAY IN THE CASCADES.  I don’t expect to see the ground appear again up at our camera location until sometime in May…or beyond.  That’s a 6 month-long snow cover!  Meanwhile down in the valleys it was a gloomy, cool, & dark day.  Most areas west of the Cascades have seen around an inch or rain…give or take a few tenths.

Today we are at the halfway point through November, which has been slightly on the cool side.  Can you believe that right now we are actually entering winter in the lowlands west of the Cascades?  It may seem like a silly statement, but in reality now through mid-February is “prime-time” for our winter weather.

Almost all of our flooding, snow/ice storms, damaging arctic blasts and (to a lesser extent) windstorms show up from now through mid-February.  Yes, I know it can snow either before this date or after mid-February, but those times are the outliers.  We are entering the main “weather action season”.

In the short term, it’s obvious we have a mild 2nd half of November coming…seems like upper-level ridging wants to linger over the western USA for a good chunk of the next 10-14 days.  Here’s the ECMWF 500mb anomaly for next Wednesday, a mild southwest flow of air

Then Sunday AFTER Thanksgiving, wet with temps near normal

And finally the last day of the month…Thursday the 30th

The last few runs of the GFS are not quite as ridgy, so maybe it won’t end up as mild as these maps would imply.  Regardless, the 12 Day trend I show many nights around 10:45pm will look like this:

The big message is that travel conditions might be very good for Thanksgiving…maybe even reasonable in the Cascades too.  #FingersCrossed

Chief Meteorologist Mark Nelsen