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

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:

 

INVERSIONS

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…

EAST WIND

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…

SUNSHINE

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.

TIME TO WRAP PIPES?

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.

CASCADE SKIING

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

 

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

  1. Jason Hougak says:

    12Z first indications of some type of change 12/21 with -4C temps and bringing in light precipitation. Let’s hope this continues to show model run consistency.

    • Jason Hougak says:

      12Z GFS

      • Ken in Wood Village says:

        I also noticed that there is a low that comes down from the NW around that time too. Hopefully, the next few model runs will keep showing this.

    • Boring Rain says:

      I recommend not getting your hopes up until it continues to show up for a few more days. Even then it could completely change but hey, if something big happened late this month or January my prediction would be right!

  2. Roland Derksen says:

    Sunny and cool here today.The view of the mountains, loaded with snow is truly lovely, but as the inversion develops it will gradually look less impressive. Very high barometer reading this morning at 30.71 inches.

  3. 31°F (-0.5°C) and frosty at my house this morning but it’s 3°C at 4000 feet and the freezing level aloft is now 6000 feet. It’s starting….

  4. Jason Hougak says:

    La Niña seems to be hitting strong in other parts of the world. Britain has snow and -6C temps. Even in Australia they are noticing its effects but not in the PNW… very interesting. Will it be dry through Christmas???

    • Jake-(Gresham near Nadaka Nature Park) says:

      Your guess is as good as mine; my thought is it has to shift. No jet stream with trough and pitches stays put in one spot for long. Count the East coast into this too. Very active Winter despite this pattern here.

      • Joshua Downtown PDX says:

        The jet stream appears to stay well to our north for at least 15 more days. The death ridge will move slowly west and slowly weaken starting mid to late next week. Even 15 days out, it is still too close to us for any meaningful precipitation. Heights and overhead temps remain above normal. It might be far enough north for So Cal to finally get some action. Record dry and boring December? Perhaps.

  5. Jason Hougak says:

    Another dry model run 0.02″… will it ever end???

  6. Temperatures between 8000 and 10000 feet yesterday evening were around -10°C and are around -4°C now. Significant warming aloft even though it’s getting cooler at the surface. Still not an inversion quite yet (temperature is still going down with increasing altitude), but soon….

  7. Ken in Wood Village says:

    I’m sorry but the model runs seem to be stupid. This isn’t winter, it’s spring/summer. I have lived her all my life and I have never seen this type of warm weather for December. It seems like a never ending summer type of weather we had back in July, August, and September. Will it never end 😦

    • JohnD says:

      Interesting–but not unprecedented–as Mark notes. The next two weeks–in the metro area, for example–will no doubt feel seasonal/cold (courtesy of December inversions) amid radiational cooling and east winds–and minus any precip! But I know what you mean: Pretty weird stuff going on overall–especially in a supposed “La Niña” cycle. All we can do is play the “waiting game” for what comes next!

      • Ken in Wood Village says:

        I know what you mean. I’m 50 years old and have seen mean different weather patterns in the Portland area but never seen this type of warm weather above 5000 ft. It’s almost like it’s a “El Niño” winter and not a “La Niña” one. I know we will have the inversion but still, the warmer weather above will kill the snow if this last for a long time. I will admit though, I will be going up to Crown Point on Wednesday when we have some really strong wind. 🙂

  8. Jason Hougak says:

    Anybody see the 18Z GFS run for the next 16 days? Max temp. 59F with max low 34F. The precipitation is rediculous 0.00″ 😆….😩

    • Well, it is the GFS and models in general have a hard time getting temperature inversions right, so I don’t expect it will be that warm.

    • Jason Hougak says:

      I know they are computer models and can change on a dime, it’s just insane to see the entire 16 day run with 0.00″ of precipitation in December.

  9. SR says:

    I’m looking forward to wind in the gorge. I work in Troutdale, so I may have to take my lunch out to the Vista House on Wednesday.

  10. Really, it’s been a while since our last long, strong wintertime temperature inversion, so I won’t mind it if that’s what we’re getting. At least the frost and fog will feel like winter. Though if it lasts a fortnight or more I’ll be eating these words.

  11. Jason Hougak says:

    I splurged and decided to take a ski day away from work. With the forecast ahead wanted some fresh powder while it is here. Timberline is currently trying to make snow but it’s more mist then snow. There are many spots with minimal coverage but it’s a comfortable awesome day to ski with the kids. I just pray something historic snowise in our future!

  12. Roland Derksen says:

    I’ll be happy if we stay dry all this week. Whatever happens next week, is too far yet for me.

  13. Ellen Wallace says:

    sometimes, if memory serves, we get some kind of precip at the end of one of these – any chance? Is it looking too warm? Thanks

    • A big cold pool in the Columbia Basin could indeed enable an ice-storm-inducing east wind for Portland during a transition event.

      That’s at least a week out so it’s hard to say. Moreover, inversions are something the current forecast models — which in general have improved greatly — still have quite a bit of trouble with. It could easily be significantly colder than forecast at lower elevations — but we won’t know until it happens.

    • …it’s going to be hard to get a good cold pool going with essentially zero snow below 4000 feet anywhere near the columbia basin and no arctic air in sight…yet…

  14. Jason Hougak says:

    Several locations in central Oregon below zero this morning on trip check.

  15. Boydo3 N. Albany says:

    Hoping this part of the Valley doesn’t end up with a continuous “fog version” for the next ten days..

  16. Jason Hougak says:

    Could it be possible to go 2 weeks in December without precipitation??? I guess we are about to find out. The model runs just keep staying drier and drier. It’ll be too mild in the Cascades to even make snow. Going to be more like spring on the slopes for December. Yikes🙄

  17. Will it snow at all this year..

    • We have almost the entire winter ahead of us, so it’s too soon to say. The big snowstorm in 2014 was in February, so there could be a big surprise in store for us later.

  18. Paul D says:

    Awesome!

  19. Sally Dixon says:

    Does wind like this impact flights at PDX?

%d bloggers like this: