El Nino-La Nina Neutral Snow in the Cascades

Whether you snowshoe, downhill ski or cross country ski you eagerly await the early Northwest winter forecasts, right? What are the early predictions? This should be easier than predicting the Presidential election correct?

Before we delve into this let’s do a quick seasonal weather forecasting 101 review. Many meteorologists have statistics that prove there is a correlation between the winter snowfall in the Washington Cascades and ENSO, the El Nino/Southern Oscillation. ENSO describes what the sea surface temperature anomalies (SST) are in the Eastern Pacific Ocean off the coast of Peru. The main area studied is close to 140 west longitude and close to the equator (this is called Nino 3.4 region).

Outside of the the Neutral phase when temperatures are normal, there are two main phases of ENSO: one is El Nino which occurs when there is above normal SST in the Eastern Pacific. The other is La Nina and this occurs when there is below normal SST. There are many ways to measure if we are in El Nino or La Nina phase and the simplest way is to see if the departure from normal is greater than or equal to ±0.50 (C). If it’s above normal SST for over three consecutive months than it is El Nino; if it’s below normal at this level than it is La Nina.  You can see what we’ve averaged on this graph:

Still with us for our weather review?

The main point in this whole discussion is that generally if there is a strong El Nino signal (SST greater than 1 C degree SST) then the Northwest generally will have above normal temperatures and below normal precipitation. So skiers, start looking at other places to ski when this occurs. However, with a strong La Nina skiers are usually rejoicing as generally a strong La Nina brings below normal temperatures and above normal precipitation; lots of snow for the Washington Cascades!

The maps below depict the “typical” weather patterns that can be associated with a strong La Nina or strong El Nino.

 

This winter will be———–?

The forecasts for the fall and early winter (October through December) give us some conflicting reports.
One of the major forecasts comes from the Climate Prediction Center (CPC), part of NOAA-National Oceanic and Atmospheric Administration. At the time of this writing the CPC states that we are in an ENSO Neutral condition. However CPC states that an El Nino is likely to form.  From October through December the CPC is predicting the Northwest will have normal temperatures and below normal precipitation; that would be not bring good news for the skiers looking for some early powder.

Another organization that provides seasonal forecasts is the International Research Institute (IRI). The IRI was established as a cooperative agreement between NOAA’s Climate Program Office and Columbia University. The IRI forecast for the fall and early winter is also below normal precipitation and normal temperatures. Skiers may again be hard-pressed to find powder.

These first two early winter forecasts are not the most optimistic if you ski or snowshoe.   Let us look at several other seasonal forecasts from private weather vendors.  One is Weather Services International (WSI) which is part of The Weather Channel. Their forecast for the Northwest ranges from below normal temperatures to much below normal by December.  However their model does not address precipitation.  This is somewhat encouraging news for us Nordic winter sports lovers and that is from the Global Climate Center. They are forecasting below normal temperatures and above normal precipitation.

Do we have a consistent winter mandate? No!

First of all, when there is a weak signal like we have now the forecasts do not do as well in terms of accuracy. I think it is constructive to look at the SST for the current phase which can best be described as a weak El Nino. Contrast this situation with 1997 which was a strong El Nino.
Map below is sea surface temperatures anomalies 9-27-2012

 

Map below is sea surface temperatures anomalies 9-30-1997

It should be obvious from the above maps that the SST anomalies in 1997 were much higher than normal; +4C off the coast of Peru and well westward which indicates a strong El Nino. In fact during the 1997-98 winter many areas in the northwest had snowfall much below normal and in California much above normal snowfall. This is what “generally” happens during a strong El Nino.

However, for the current year the temperatures are close to 0.50 to  1 C above normal near the Peru coast  and as you go westward to 140 degrees west longitude they are  close to normal. Another factor indicating a weak El Nino is that at least half of the forecast models indicate a weak El Nino (SST at or below 0.5 C). The chart below indicates this. The color lines are the forecast models.

Other Factors besides ENSO?

There are other indices used in seasonal forecasts.  One that can impact the Northwest is the Pacific Decadal Oscillation (PDO). PDO refers to the sea surface temperatures from the coast of Alaska south to the Washington, Oregon and California coasts. Currently we are in a cool phase PDO (below normal sea surface temperatures) which can intensify a La Niña phase or minimize the impacts of an El Nino.  There are many other indicators and weather patterns that impact seasonal forecasts and space in this article does not permit discussing all of these.

Conclusion
At this point it is frankly too early to have much confidence in a seasonal forecast.  Some forecasters are suggesting average winter conditions for the Northwest winter and I would tend to agree with that. However things can and do change. It is best to monitor different web sites to see if there have been any changes. Some sites to utilize are NOAA’s Climate Prediction Center or the International Research Institute’s seasonal climate forecasts.