Thursday, August 4, 2011

Double Dip La Nina?

The Climate Prediction Center has issued it's latest ENSO advisory, which suggests that either ENSO-neutral or La Nina conditions for this coming winter.

WTH is ENSO-neutral?  It basically means that the sea surface temperatures in the tropical Pacific Ocean are pretty close to average and that neither El Nino (warm sea surface temperatures in the central and/or eastern tropical Pacific) nor La Nina (cold sea surface temperatures in the central and/or eastern tropical Pacific) conditions are present.

Currently, sea surface temperatures in the tropical Pacific are very close to average (i.e., within 1C).

Source: NOAA/CPC

The atmospheric circulation and areas of convection, however, still reflect what we expect from La Nina.  Thus, oceanically this is a neutral situation, but in the atmosphere, conditions are still a bit La Nina like.

For this coming winter, the models that are used to forecast ENSO are, to use a technical phrase, "all over the place."  Some models predict a return to La Nina conditions, most members of the NCEP Climate Forecast System ensemble.

Source: NOAA/CPC

The bottom line is that we have some forecast tools suggesting ENSO-neutral conditions, and others suggesting a return to La Nina conditions for this winter (a.k.a. the double-dip La Nina).  The CPC is understandably calling for ENSO-neutral conditions for the fall and either ENSO-neutral or La Nina conditions during the winter.

What dis this mean for winter in the Wasatch?  Practically nothing.  The ENSO phase does not strongly correlate with snowfall in the Wasatch.  Some years are big (like last year), others not, others near normal.  Even if things end up on the dry side, it's always good to remember that a bad year in the Wasatch is better than a good year just about anywhere else. 

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