NOAA’s Climate Prediction Center has given a 50/50 chance for the transition into an El Nino phase this fall. This isn’t likely to be another moderate El Nino, this could be an extreme event. Skiers likely know more about the the El Nino/La Nina (El Nino Souther Oscillation) cycle than most people because of its impacts on snowfall patterns. However, the NOAA forecast from March 24 looks a bit conservative compared to other models and forecasts.
Annual average temperatures vs average 1951-1980. chart: NASA
An El Nino event in 2014 or 2015 would likely be a record breaker. Global temperatures have trended higher across both El Nino and La Nina events. And the recent ‘stall’ in global temperature rise occurred on two La Nina years. The warmest year on record, 2010, was a mild El Nino event, and 1998 was a record El Nino event. While the temperature differences may not seem that big, these are taken over an entire year. Sure, maybe most days feel the same, but we definitely notice when storms come in hot, drenching the mountains in rain.
The current ENSO (El Nino Souther Oscillation) phase is neutral, indicated by Sea Surface Temperatures over the equatorial pacific that are within 0.5 Celsius from average sea surface temperatures. El Nino events are caused by a reversal or breakdown in trade winds, that normally push equatorial water West into Indonesia, and the pooling of warm water along the Eastern Pacific. This increase in sea surface temperature affects weather patterns worldwide.
A recent German study puts the probability of El Nino much higher, around 75%, while a study from Columbia University indicated a 60% probability. Paul Rondy, professor of meteorology at Albany State University, New York, puts the chance of an extreme El Nino at approximately 80%. The Australian Government, interested because El Nino can cause severe drought across Australia, also monitors the Southern Oscillation Index (SOI). Negative SOI index values, calculated from pressure data in Darwin and Tahiti, have remained strongly negative, which are correlated with El Nino events.
There has been an observed patterns of events similar to those before the 1997-1998 extreme El Nino event, but of larger magnitudes. These strongest of these observations are the reversal of trade winds, instead of blowing at 10 knots from the East, bursts of up to 30 knots have been observed from the West, and Kelvin waves. Kelvin Waves travel beneath the sea surface and transport pockets of warm water (that are several hundred kilometers long) Eastward towards South America. Kelvin Waves are created by West Winds acting on subsurface waters, and recent observations show the water in these waves is up to 9 degrees celcius warmer than the surrounding water. This difference in temperatures is larger than what was seen prior to the 1998 El Nino.
Graphics showing temperature anomalies at depth and temperatures at depth (imagine looking into the side of a fish tank). The upper graphic shows the most recent observations of the kelvin wave and warm water headed East. charts: NOAA
The Kelvin wave actually moving East, pretty dang cool to watch! from: NOAA
While this summer could be a record breaker, nothing is set in stone. Currently, equatorial winds continue to come from the West, but a breakdown and a return to normal trade wind patterns would move the warmer water Westward towards Indonesia, reducing the chances of an El Nino event occurring this summer. Unless this pattern changes, it looks like we are headed into an El Nino.
El Nino has an effect on temperature and precipitation patterns. During El Nino events the pacific jet streams straightens travelling Eastwards across the U.S. and bringing in storms on a more Southerly track. This weather pattern favors the Sierra Nevadas and Southern Rockies, while areas further north tend to have a warmer and drier winter. During the 1997-1998 extreme El Nino event Donner Summit received over 40 feet of snow. On a global scale, a strong El Nino event in 2014 or 2015 could set a new temperature record. The moderate El Nino in 2010 set a new high temperature record of 128.3 F in Pakistan (yes, its hot there, but that is really hot).