Friday, August 21, 2015

CPC Gives Northern Utah Skiers No Love

The NOAA/NWS Climate Prediction Center (CPC) issued their latest three-month outlooks yesterday and they give northern Utah skiers no love.

For December through February, they give northern Utah slightly elevated chances of above average temperature and slightly elevated chances of below average precipitation.

Source: CPC
Source: CPC
Does this mean we're in for another warm winter with bad snow?  No.  In the images above, equal chance (EC) areas in white are not projected to have an average winter.  Instead, EC means that the likelihood of below average, average, or above average temperature or precipitation does not differ from their climatological odds of 33.3% each.  In other words, the tools available for seasonal forecasting do not allow us to anticipate a strong loading of the seasonal climate dice one way or the other.  Areas in red (temperature) or brown (precipitation) are areas where the likelihood of above average temperature or below average precipitation, respectively, are higher than climatology.  So, for northern Utah, they are giving us just slightly higher than climatological odds of above average temperature and below average precipitation since the odds are between 33% and 40%.  In other words, the seasonal climate dice are loaded just slightly on the side of above average temperature and below average precipitation.

These outlooks are based on a variety of tools including seasonal climate forecasts, composites (averages) of past years stratified by El Nino, La Nina, and neutral conditions (this year they are banking on El Nino), and a few other statistical tools relating past weather to various factors.  El Nino composites typically feature a precipitation dipole with below average precipitation over the interior northwest and above average precipitation over the southwest, roughly consistent with the outlook above.  Below is the average precipitation anomalies from three ensemble suites produced by the NCEP Climate Forecast System (CFS) for December to February.  I've drawn a black line at the approximate position of the central Wasatch.  Each of these ensemble means has a dry northwest and a wet southwest relative to climatology, with the central Wasatch in the transition zone.

Source NCEP
Keep in mind that the composites generated by CPC use very coarse precipitation data that does not specifically look at the central Wasatch, while the CFS does not resolve the Wasatch in any way, shape, or form.  Thus, one needs to be cautious in interpreting these outlooks and projections.  We can, however, use past data from Alta Guard to stratify central Wasatch snowfall by El Nino, La Nina, and Neutral and even strong El Nino and La Nina events, as we have done several times in the past (e.g., El Nino Likely for the 2015-16 Winter).  You probably know the story here.  Not much signal in the noise.  We've boldly put a linear trend line on the data, which does show a very small trend to lower values as one transitions to strong El Nino, but the scatter is so large that I think that's neither physically or statistically significant (we haven't bothered looking at the latter).  Note that this is for various 3-month periods during the cool season, not specifically December to February as in the plots above.  This scatter exists because: (1) Utah sits in the transition zone between the El Nino/La Nina precipitation dipoles, (2) other factors affect the seasonal climate besides El Nino, and (3) there is always some randomness in the weather that occurs during any given season.  

So, we may be looking at a Godzilla El Nino, but for the central Wasatch, that means nothing.  Don't fall for the hype.  For the central Wasatch, we really have no idea what kind of winter we are going to have.  It could be big, it could be bad, or it could be average.  Further, the amount of snow we get isn't always as important as when it comes and how it comes and those details are even more uncertain.  


  1. I couldn't help but notice the incredibly negative precipitation anomalies predicted across the Equatorial Atlantic. Looking around, negative anomalies there appear to be normal for an El Nino, but not to that extent, and I wonder what is driving it (in the models, at least).

  2. Very well put's nice to see another fellow meteorologist with a more realistic view of the upcoming El Nino. Seems like a coin toss to me as well.

  3. I'll settle for "average" this season!!!

  4. Could you show what this map looked like for last years prediction? Looks similar if I remember correctly

    1. You have an excellent memory. See the DJF plot in

      There was an expectation of a moderate El Nino developing for last winter, but it was late in getting going.

  5. First winter in SE Alaska isn't looking so good;) Oh well.......