WeatherWatcher: el Nino and la Nina explained

By Carl Dinse, WeatherWatcher for the ShorelineAreaNews

ENSO (El Niño, La Niña) What does it mean for us?

ENSO is an acronym for El Niño Southern Oscillation. The Oscillation occurs in the eastern Pacific along the Equator. There are three different modes for the ENSO, El Niño, La Niña, and neutral. Typically this pattern occurs during the late fall, winter, and early spring seasons for the Northern Hemisphere. However some may last all the way through summer and continue into the next winter. In spring NOAA has what is called the Spring Block, where they can’t predict easily what the ENSO is going to transition to until after March or April.

Here’s the short and sweet as what each mode means for Shoreline and Lake Forest Park.

• Neutral: This typically means we will have a normal winter, average precipitation, and average temperatures.
• El Niño: This means our winters will be warmer than average, with less than average precipitation.
• La Niña: Causes cooler than normal winters, with higher than normal precipitation.

El Niño winters are the biggest cause of our water shortages we have some years in the summer following, due to a lower than normal snow pack in the mountains. La Niña years can generate excessive snow packs, and rain, or snow events even to our area. Depending on the strength of the modes, depends on the weather severity. Also it is very important to note, even if the weather is expected to be cooler, and wetter than normal, it doesn’t necessarily translate to more snow events in the lowlands, however they do tend to increase on some La Niña years. The same goes for El Niño years, we might have no rain or snow events, or we might have a snow event and normal rain storms. It all depends on the strength. Take it as just a general outlook, nothing specific, after all forecasters can barely predict a week in advance, let alone a whole season. That being said, here’s some data that shows the difference between an El Niño year, and a La Niña year.

The winter of 2009/2010 was an El Niño year. This past winter, 2010/2011 was and still is a La Niña year.

Here is a line graph that compares the daily average temperatures from November – end of March against the 2009/2010 El Niño and the 2010/2011 La Niña.

Daily Average Temperatures compared.

Here is a bar graph that compares the monthly total rainfall of the winter of 2009/2010, and 2010/2011, from November to March.

Rainfall comparison.

You can see how the 2010/2011 winter is wetter, and cooler than the 2009/2010 winter.

About once a month I will write a short report on the ENSO status, and forecast and what it could mean for all of us here in Shoreline and Lake Forest Park.