April 11, 2012

Goodbye La Nina

 Weekend Forecast and Discussion of Heat Islands on KPLU

Finally, La Nina's days are numbered, and its expression in the ocean and atmosphere are beginning to fade.   In two months, it should be history, which is fortunately for us in the NW, where it brings cool, wet weather.

Here is the proof--something to savor.  Lets start with the key index that meteorologists look at, the sea surface temperature anomaly (difference from average) in the central Pacific (the 3.4 area, see map

 Here it is.  The cold anomaly (a sign of La Nina is rapidly fading)

Now lets check under the sea surface to see what is happening, since surface temperatures can be deceiving.  Here is an east-west cross section under the central Pacific, showing you the water temperature anomalies down to 300 meters (red and orange warmer than normal, blue is colder). The panels start in February, with the latest one April 3.  Notice how the blue colors with depth in the central and eastern Pacific have faded, with warmer than normal temperatures taking hold.   Very bad for La Nina.

A number of organizations run statistical and dynamical (simulating the temperatures of the Pacific) models of La Nina/El Nino and here are the latest results:

Virtually all the models are taking us to neutral conditions (temperature anomaly near zero) during the next few months, with some even heading towards El Nino by next winter (large warm anomalies).  Plus it would be extremely unusual to have three La Nina years in a row.   So we can rest easy about the end of La Nina.

Since it will take months for La Nina to fade and the atmosphere to reconfigure itself, don't expect a sudden transition to warm and dry conditions.  Besides, the correlation between La Nina/El Nino and our weather fades as we move into the warm season.  But the implications for next year are substantial, particularly after the New Year.  Years in which the sea surface temperature anomalies are near zero (neutral or La Nada years) are climatologically normal except for one thing:  the biggest of the big weather events (floods, windstorms, etc.) like neutral years.

The long range forecast models, both U.S. and European Center (ECMWF), suggest a good weekend, particularly on Sunday.  Here is the ECMWF upper level flow (500hPa) forecast for Saturday and Sunday mornings.   A ridge is moving in on Saturday and will be over us on Sunday, with a trough messing up weather over the southwest U.S..  I would worry about some serious thunderstorm activity on Monday from Texas, OK, and eastward, as the uplift from the trough reaches the SE U.S.
PS:  Some good news for those who like Seattle's roads clear of ice during the winter.  The city of Seattle is now putting several road temperature sensors on bridges and other locations around the city.  This will greatly assist SDOT in knowing that is going on during the winter-- a major advance.    Imagine what the TV snow/ice hypsters will do with this data! And we have some major improvements in mind for SNOWWATCH.


  1. Check out this neat Art Project that graphically displays the wind currents for the US. Found a link to it through Orcas Power & Light (OPALCO) site. http://hint.fm/wind/

  2. Cliff, 'sorry to use comments to reach you, but seemingly no other option. This post of yours is the first one failing to show up properly on Google Reader. If I press the "reload" button, I get the message "Sorry, an unexpected condition has occurred which is preventing Google Reader from fulfilling the request." If I hit reload again, it serves up your last post (Warmth).

    Thanks again for all the effort you expend keeping the public up to speed. I just listened to your spot on KPLU. Hmmm, I think I'll send KUOW another reminder that my public radio support moved with your weekly weather spot!

  3. Cliff, a follow up: Your next post (birds on Doppler) showed up properly on Google Reader, so only this post has the GR issue embedded in its dark innards. Hooray!

    I recommend Google Reader to anyone following Cliff Mass Weather Blog. Since Cliff created this fine information source, I've had to check in 2,3,4 times before finding a new Mass Posting. Of course, GR is free and I found it very easy to set up. The GR tab stays open 24/7 in my Chrome, and I use a small free widget from Google Labs which shows unread posts as a tiny number displayed in the GR tab. No clicks, just a glance tells you of a new post.

    And a thousand thanks to The Clare's for that TERRIFIC FIND wind animation link! The finest execution of turning scientific data into a work of art that I have ever seen. I've already sent its creators an email begging them to link their daily frames into a longer animation. I'd pay the cost of a Hollywood movie to have a DVD of one year of these data. Mesmerizing! It's a bit counter-intuitive that nerdy computers can find such stunning beauty in the streams of data we all now have at our fingertips. Thanks!

  4. I'm curious: When you say that having three consecutive La NiƱa years would be extremely rare, how rare do you mean? Has such a phenomenon ever been recorded?


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