El Niño Is a Lock But Snow for Wasatch Less Certain

The National Weather Service Climate Prediction Center (CPC) issued their monthly El Niño/Southern Oscillation (ENSO) Diagnostic Discussion today and El Niño is looking like a lock for this winter.  They give a 90% chance of a very strong El Nino during Northern Hemisphere fall and winter.  

By most definitions, a strong El Niño is already in place over the Tropical Pacific Ocean.  Sea surface temperatures more than 1°C above average already extend westward along the equator to nearly 180° with areas more than 3°C above average near the coast of South America.  Anomalously warm sea surface temperatures also extend poleward to the west of North and South America.  

ENSO strength probabilities from CPC are near or above 90% for September-November through November to January.   The odds of a strong event decline later in the winter, although the odds of El Niño conditions persisting remain high.  

El Niño is a tropical climate phenomenon with impacts even in the mid and high latitudes as it affects jet stream and storm track patterns.  During Northern Hemisphere winter (December – February) over North America, El Niño can be associated with anomalous warmth of Alaska, western Canada, and the northwest United States and wetter conditions in the southern US and northern Mexico.  Linkages to the mid and high latitudes are weaker in summer.  

Source: https://www.climate.gov/news-features/featured-images/global-impacts-el-ni%C3%B1o-and-la-ni%C3%B1a

For the Wasatch, the relationship between El Niño and snowfall is relatively weak.  It is popular for people to look at past events for analogs, but there isn't a true analog to this event and strong events are relatively rare during the historical data period, so the sample size is small.  Additionally, El Niño is an important factor, but there are other phenomenon that can influence the weather in any given winter, including the possibility that what happened in a previous strong El Niño year more strongly reflects randomness than a real signal.  The CPC outlook (now almost a month old so maybe there will be an update) still puts northern Utah in the "equal chances" category for December to February precipitation, meaning they don't consider there to be better skill than chance for what will happen this winter in our neck of the woods. 

Source: CPC

They are, however, giving better odds for above average temperatures, although that's not all that surprising given recent trends. 

Source: CPC

My view is that the usefulness and reliability of these seasonal outlooks for anticipating what the ski season will be like is limited in the Wasatch.  In addition to the limited correlation in our part of the world, how the snow comes and how the temperatures fluctuate matter.  A warm winter can yield a good snow year at low elevations if the storm characteristics are right.  A year with above average snowfall due to big snows in November and December is very different from one with big snows in March and April.  

As such, I'm comfortable saying that I can't confidently predict how this coming season is going to play out in the Wasatch.  It's probably better to spend your time getting in shape for ski season than worrying about what the season will bring.