El Nino conditions have developed and are very likely (>90% chance) to persist through the 2015-16 winter. The developing El Nino has started to receive attention and so we would like to take a moment to answer some of the common questions that arise when the topic of El Nino comes up...

What is El Nino?

El Nino is a state where the water temperatures in the Pacific Ocean near the equator become abnormally warm. This is a natural cycle that repeats itself on average about once every 2 to 7 years. El Ninos tend to begin in the summer and usually peak in intensity during the following winter.

I don’t live near the equatorial Pacific, why should I care if the ocean is warmer there?

The unusually warm waters in the Pacific Ocean cause a ripple effect in the atmosphere with weather patterns across many areas of the globe altered as the warm waters help shift jet stream patterns. The map below highlights some of the typical impacts from El Nino across the globe.  Notice that it often results in droughts in some areas while heavy rain and flooding occur in others.

The effects of El Nino in our region tend to be most pronounced during the winter, when moderate to strong El Ninos typically produce warmer than average temperatures and below average precipitation.

Has the current El Nino had impacts on the weather patterns yet?

The typical warm season El Nino patterns have most definitely already become evident. First, El Nino typically results in a more hostile environment for tropical storms and hurricanes in the tropical Atlantic Ocean and that has certainly been the case this year. There have yet to be any tropical systems in the deep tropical Atlantic and the Caribbean region is experiencing drought conditions. The tropical Pacific on the other hand has been abnormally active, in particular the Central Pacific in and around Hawaii where there have already been 2 tropical storms that have threatened the state, a phenomenon that is quite rare, particularly so early in the season. 

How is this El Nino comparing to previous El Ninos?

It is important to note that no 2 El Ninos are exactly alike and no 2 El Ninos produce exactly the same impacts on weather patterns. The index that is commonly used to measure the magnitude of the El Nino is already trending toward this El Nino developing into a strong El Nino, similar to the 1982-83 and 1997-98 El Ninos, which both ended up being among the strongest El Ninos observed since 1950.  Experts at NOAA’s Climate Prediction Center are now forecasting the current El Nino to be similarly as strong as the 1982-83 and 1997-98 El Ninos.

What were the 1982-83 and 1997-98 winters like in this area?

Both winters were abnormally warm and featured only about half the average snowfall during the Dec-Feb period. Interestingly, both years saw significant snowstorms during March, which helped push the annual snowfall totals up closer to normal. Temperatures were above to much above average all 3 winter months during both winters, peaking at +7.1F above average in December 1982 and at 12.4F above average in Feb 1998.

If this El Nino is going to be strong like 82-83 and 97-98, then that means this winter will be very warm like those winters, right?

The odds certainly favor a warmer than average winter and below average snowfall during the upcoming 2015-16 winter, which is what NOAA’s Climate Prediction Center is currently forecasting.  The forecast below was issued on August 20th.

It is, however, important to remember that no 2 El Ninos are alike, and even if this year’s El Nino is similar in strength to 82-83 and 97-98, it is not a guarantee that the weather patterns will end up exactly the same. Comparing current Pacific water temperatures to water temperature to those from 1982 and 1997 shows similarities, but one striking difference is the incredibly warm waters farther north in the eastern Pacific.

That abnormally warm water actually extends all the way north off the U.S. west coast up into the Gulf of Alaska. It is unclear if this anomaly will persist through the upcoming winter, and if it does, how and if it will alter the weather patterns from those of a typical moderate to strong El Nino. It has been theorized that these abnormally warm water temperatures, which were present the past couple winters, were a contributing factor to the recent abnormally cold winters. 

How is a winter officially classified as abnormally cold, warm or normal?

The high and low temperatures for each day during the winter are added together and divided by the number of days to determine the average temperature for the winter. This average temperature for the winter is then compared against the 30 year normal average temperature for the winter to determine how close they are. It is important to know that even abnormally warm winters can and often do experience spells of cold and snowy weather, just like abnormally cold winters typically experience thaws.

When was the last El Nino?

The last El Nino was back in 2009-10 and was a moderate El Nino. That winter actually ended near to slightly cooler than average as other atmospheric circulations mitigated the effects of the El Nino some. This is reminder that no 2 El Ninos are the same and there are other factors that could play a role in our winter weather and result in the 2015-16 winter not being as anomalously warm as previous strong El Ninos.

Additional resources and information on El Nino can be found here:

2 min YouTube video on El Nino

https://www.youtube.com/watch?v=_Tuou_QcgxI

Latest Climate Prediction Center technical El Nino discussion:

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html

NOAA El Nino informational Page:

https://www.pmel.noaa.gov/tao/elnino/el-nino-story.html

Historical El Nino/La Nina Index Values:

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml

El Nino FAQ:

https://www.pmel.noaa.gov/tao/elnino/faq.html#often