December 23, 2011

The Big Shift in Our Weather

Mother nature has a holiday gift for you--a major shift in  our weather pattern.  For roughly three weeks, the Northwest has been preternaturally dry, you would think we were living in Palm Springs!  For example, Seattle-Tacoma airport has only received .25 inches this month, 3.61 inches below normal.  Yesterday, sun was nearly everywhere and seasonal affective disorder (SAD) cases are surely down this winter.

It all ends this weekend.

Instead of the high-amplitude, persistent ridge in the eastern Pacific the atmosphere will transition to what meteorologists call zonal flow, in which the jet stream, and the strong flow associated with it, head straight into our region.   Embedded in this flow there will be low pressure systems and fronts that will bring rain and wind every day or so.  Temperatures will warm into mid-forties each day, clouds will never leave us, and fog and frost will be far less likely--normal weather for us mid-winter.

I am deathly afraid that this pattern will end our chances of being the driest December on record.

Just to illustrate, here are two upper level maps at a level where the jet stream is generally strong (300 hPa, roughly 30,000 ft) for today and next Wednesday.   The shading gives the wind speeds. See the difference?  Ridge versus zonal flow.  You can think of the jet stream as the atmosphere's fire hose....and we will be on the receiving end.

 With strong zonal flow it becomes increasingly difficult to get the timing of weather systems right--so don't be surprised if forecasts are off by 6 hrs or so, particularly for forecasts a few days out.

On vacation and want to escape this onslaught?  Can't afford the exorbitant fares to Hawaii?  Head to southern California.  They will be sunny with temperatures heading into the upper 60s and 70s.  No rain.  Lots of sun.  Ironically, the ridge has brought us the dry, sometimes sunny weather, produced cooler than normal conditions in the SW U.S. since there is cool northerly flow to the eastern side of the ridge.   But with the ridge gone, southern CA temperatures will rebound.

And one more holiday gift....nearly all the long-range models indicate La Nina will disappear over the summer and next winter will have a very different character.  

Happy Holidays....


  1. Well, I hope we don't mess up the record dry December, but I would like some snow.

    Whaddya think? Snow in the Portland/Vancouver area any time soon?

    Merry Christmas and thanks for all the data you provide!

  2. Cliff,

    It might be a bit premature to make a forecast for next winter. According to Klaus Wolter at NOAA:

    "I believe the odds for this La Niña event to continue right through early spring (March-April 2012) are higher than 50%. Beyond that, it is worth noting that of the ten two-year La Niña events between 1900 and 2009, four ended up as a three-year event, so I would put the odds for this to occur in 2012-13 at 40% right now. Interestingly, the other six all switched to El Niño, leaving no ENSO-neutral case. Will be interesting to see how 2012 evolves."

  3. @Snapdragon,

    I'm an amateur meteorologist in the Portland area (amateur meaning I have a degree but I haven't gotten a job yet). I run a forecast for the Portland area, so you can imagine I keep an eye out for the possibility of snow. Sadly, I'm not seeing any real snow event conditions developing in the longer models (384h out), but I don't have access to as many models as Cliff probably does so maybe he has seen something more promising.

    What I've seen has been along the lines of the jet stream continuing to aim right for us, or close to us, at least through the first week of January. But that could always change.

    I know I'm no Cliff, but I just thought I'd give my 2 cents.


    Given that both of these La Nina's have had a shift in the position of the ridge (this year's obviously being much more pronounced), I was wondering if there is some thoughts that maybe an ENSO neutral or El Nino 2012 would end up being more interesting than you might think at first. I guess I'm just sort of mulling ideas around in my head. I don't have any meteorologists around me to discuss this sort of stuff with.

    Anyways, sorry for the long post.

  4. Mother Nature's "gift" can suck it. It is winter - where is the cold and rain and snow!? Now THAT would be a gift! :)

  5. "Deathly afraid..."

    Thanks for the chuckle, Cliff!

  6. Thanks for being the bearer of better news. We'll take it. But its still not anywhere near to a snowy pattern.

    I would estimate my particular location in E. Wash. has a brown Christmas 1 in every 7 to 10 years. Even worse, our surrounding ridges up to 5000+ ft don't even have a flake on them. Thats probably 1 in every 40 to 50 years. Maybe unprecendented.

  7. Justin W.
    Sounds like you know what you are talking about- thanks for the info! I won't be holding my breath for snow any time soon. (But I might go get my car washed- that seems to always bring snow...)

  8. OH please no. I hope you're not hinting at an El Nino next winter. I can't handle another warm, dry, and boring winter. Why can't we just have a normal neutral winter. I use to cheer for La nina, but last winter was a dud and this winter has been more boring, so far..... I'm still holding out hope for La Nina in mid January through March, but it has a lot of work to do.

  9. hey hey hey. Tonights free sample MSL and 850hPa EURO shows a decent landfall storm at 168hrs. First run I'd always discredit it. But this year, I'm running with it, lol. Nerdy sense of humor.

  10. Taiwan has had no sunshine... a bit weird for them in December.

    I'm not sad about the lack of snow and actually hope it continues into January. My husband is having major heart surgery next month and I'm going to have to manage the kids and driving to Seattle every day on my own... I HATE driving in snow!

  11. El Niño / ENSO-neutral conditions next year?

  12. I'm still pretty amazed that--with all the vast amounts of meteorological modeling and super-computers, the mountains of data and experience of people like Cliff Mass--how weather forecasting can be so imperfect (or completely wrong!).

    "It all ends this weekend." ...??

    On Saturday in Ballard there was unbridled sunshine with beautiful clear views of the Olympics.

    On Sunday we had less than 0.01" of rain during a very brief event. Even now, as I type this at 9:30pm...I see the glow of Jupiter high in the starry night sky.

    To think that one can forecast what El Nino/La Nina will do a year from now seems a bit nutty when this weekend's forecast was so completely off.

    Why not just flip coin?

  13. Cliff - I live in Poulsbo, and yesterday we had a really unusual event - at least according to NOAA. The temperature rose 16 degrees in an hour, and then fell again over the next 3 hours - the wind shifted and gusted - you can see it in the 3 day history starting about 6AM in Quilcene. thought you might have some interest in this very local event, as well as an explanation..?

  14. Cliff~ the nws seems to be watching the friday storm quite closely... Is it just a stronger than usual system or something to be really ac concerned about (like the 2006 storm?). Also, sundays storm looks like it may have even stronger winds...what's your take on these storms?

  15. Elf said "hey hey hey. Tonights free sample MSL and 850hPa EURO shows a decent landfall storm at 168hrs. First run I'd always discredit it. But this year, I'm running with it, lol. Nerdy sense of humor." December 24, 2011 12:23~~~~~~~~~~~ I saw that too! The nws is concerned about the friday night storm, but the sunday storm looks way more intense to me. This could get interesting, maybe? Welcome back La Nina!


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