Whose Fault Is It? Could It Be El Nino, La Nina, or even La Nada?

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Snowfall 2011 South Hills | Image Tim Chuey

Is it El Nino, La Nina, or maybe even La Nada? You have heard those terms bandied about by meteorologists and news anchors alike, but what do they really mean and why should you care. The three terms describe the sea surface temperatures in the Pacific Ocean which have a significant effect on the weather patterns around the world and particularly over the Pacific Northwest.

I’ll start off with the definitions of the terms so we can then use them to explain how they specifically control our weather patterns, particularly during Winter.

Latest Sea Surface Temperatures Pacific Ocean | Image NOAA
Latest Sea Surface Temperatures Pacific Ocean | Image NOAA

El Nino is defined as a warm water current (shown in red/orange) that appears annually, around Christmastime, along the coasts of Ecuador and Peru. The name El Nino means the boy child and refers to the “Christ Child” who’s birthday is celebrated in December when the warm water pool extends itself closer to the South American coast. It was first discovered or noted by the fisherman who found warmer water where they usually would catch fish.

La Nina is defined as a cold water current (shown in blue) that appears annually, around Christmastime along the coasts of Ecuador and Peru. The name La Nina means the girl child and is the opposite of El Nino and is the cool water pool that extends itself closer to the South America in December.

It seems obvious that El Nino and La Nina can’t occupy the same area along the South American coast at the same time. That is where another term comes into play. The ENSO or El Nino-Southern Oscillation. El Nino is often called the warm phase of ENSO while La Nina can be called the cold phase of ENSO. Often the sea surface temperatures waver between the two in the same season.

Just when you thought I was finished giving you definitions I have one more. What would you call it when neither El Nino nor La Nina come to visit the West Coast of South America? I guess you could call it the “nothing” and that is just what they decided to call it. In Spanish it is La Nada.

The Jet Stream | Image ww2010atmos.uiuc.edu
The Jet Stream | Image ww2010atmos.uiuc.edu

Now that you have the key definitions we need to find out how they can make our lives more pleasant or more difficult. What these currents do is deflect the Jet Stream in such a way to either bring the colder air and the Winter storms our way or to act as a barrier to protect us from the stronger WInter storms and keep us warmer.

El Nino’s warm water pool actually deflects the Jet Stream in the Winter in such a way as to set up a high pressure ridge over the Pacific Northwest. (See Picture to left)  That ridge keeps the cold air and the Winter storm track to our North or South and tends keep us warmer and drier. During an El Nino year there is less tropical storm activity in the tropical Atlantic due to increased vertical wind shear over the area.

Vertical Wind Shear Diagram | Image AMOL/NOAA
Vertical Wind Shear Diagram | Image AMOL/NOAA

Vertical wind shear is the change of wind direction with height. In order to build the storm clouds it takes to produce a hurricane there must be steadily rising columns of air and the change of wind direction as the air is rising tends to stop the development of the storm clouds.

La Nina’s cold water pool has the opposite effect and deflects the Jet Stream so as to send the Winter storms right at us. I know what you are expecting me to say next. Which one is controlling our weather now and what kind of Winter can we expect? The experts say we are in the La Nada now. It is a bit early in the season to make a solid prediction for Winter. The best time is mid-November when the sea surface temperatures are set up for the Winter months. That prediction would be for the actual Winter months of December, January, and February. As of now the sea surface temperatures indicate neither El Nino or La Nina so that leaves us with La Nada continuing and neither the cold water nor the warm water dominating. That makes for a difficult forecast. My best guess is that this Winter will be very similar to last winter. That means no major snowfall down on the Valley floor. Remember that this is only an educated guess at best and should be updated when the new winter prediction computer model from the National Weather Service produces the national forecast for October, November, and December. That should be ready soon. It takes a very small change in data for an unexpected storm to appear. That is what makes weather forecasting such a challenge.

Let me know what you would like me to talk about or explain. You can email me at: [email protected].

Tim Chuey is a Member of the American Meteorological Society and the National Weather Association and has been Awarded Seals of Approval for television weathercasting from both organizations.

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