El Nino Outlook 2015
The El Nino phenomenon can have a big impact on the climate across the lower 48 states through the course of a year, especially late winter and into spring time.
Here is a refresher on El Nino, simply put, it is when water temperatures are above normal in the subtropical Pacific, especially near the equator. This warmer stretch of water can extend across almost all of the Pacific Ocean.
These warmer waters can alter the course of the jet stream (can even sometimes produce a southern branch of the main jet stream). The warmer waters can also have a big influence on the distribution of precipitation across the United States. Some areas can get quite wet, some areas can go dry and many areas experience warmer temperatures.
It is important to note that no two El Ninos are the same. They come in different shapes, sizes and outcomes. However, there are certain trends you can count on when an El Nino forms.
This past year a very weak El Nino (also known as a Modiki El Nino) formed about this time last year. It was a borderline El Nino as water temperatures were just slightly above normal, however, we have seen recent trends where it has become a little stronger over the past month.
There was a lot of excitement last year that a strong El Nino was going to form this past year, this was especially true for folks in California where strong El Ninos in the past have led to above normal rainfall and Sierra snowpack.
In the graph below you can see the frequency of El Ninos back to 1950. The red highlights periods of warmer water in the subtropical Pacific, blue represents periods of colder water temperatures (La Nina).
As you can see, this past year, the warmer water temperatures fell well short of the stronger El Ninos in previous years (especially the super El Nino of 1998). All indications suggest that warmer water temperatures in the subtropical Pacific will again take place during the coming year. In fact, while not expected to be a strong El Nino, it will likely be stronger than this past season. This could bode well for parched California, portions of the central and southern Rockies and the Southern Plains.
The chart below shows a variety of different weather models forecasting the upcoming 2015/16 El Nino season.
With the exception of two models, the rest of the modeling is prediction warmer than average subtropical Pacific water temperatures through January 2016.