La Nina Update: Turning Strong

October 8, 2010

I spent some time today looking at lots of different numbers, indices, and historical information related to La Nina.   It appears that La Nina is now tipping into the “strong” category and models indicate it may strengthen further the next few months.  This is easily now one of the strongest La Nina events since 1950, along with:  1955-56, 1973-74. 

Now that’s using the ONI (Oceanic Nino Index).   Each of those events reached the -2.0 or lower threshold according to NOAA.  1988-89 was very close…a -1.9.  That’s splitting hairs a bit and we won’t know how low the number actually goes this year until all the excitement is pretty much done this winter.

There are other measurements…one that Jim Little and I used to watch a lot in the 1990s is the Multivariate ENSO Index.  Thanks to Steve Pierce for bringing this to my attention again today.  It was in one of his dozen daily emails that keep the local media informed of ANY changes to our weather.   Here is an image and discussion from Klaus Wolter of NOAA’s Earth System Research Laboratory that goes along with the graph:

   

You can read his discussion which is quite interesting, but also notice how rapidly it has dropped the last few months.  According to Wolter “…One has to go back to July-August 1955 to find lower MEI values for any time of year.”  Basically according to this index it’s the strongest La Nina since 1955!  You can see that in the chart.  Eventually the ’54-56 event went slightly lower (than our current La Nina SO FAR).  This index uses more than just sea surface temperatures, it factors in quite a few other variables.

Just for fun, what happened in Winter 1955-56?  Several arctic blasts, including the earliest big freeze we’ve had in mid-November, then a couple more arctic blasts in later January and February.  By the end of the winter Portland Airport had seen 13 days where the thermometer never climbed above freezing.  Wow…cold.  22.4″ of snow that winter at PDX too.  The 2nd snowiest La Nina winter in Portland.  I notice very heavy snow in the Cascades and foothills too.  Packwood, WA (1000′ elevation) had 82″ that year!

That was just one winter though.  The other two big La Nina years mentioned in the first two paragraphs?   No snow one year and only 3.2″ the 2nd.  But both had at least either one or two arctic blasts with winter lows of 9 & 12 degrees at PDX.    1973-74 is the all-time record winter snowfall at Government Camp too…474″

By the way, if this is the first you have heard about La Nina on this blog, check out the tab above labelled LA NINA 2010.  All the images and info about it so far are on the post.

Chief Meteorologist Mark Nelsen