Wednesday, October 10, 2012

“Do You Think He’s Coming Back?” 
– From The Dark Knight Rises 

2:10 PM EDT 10/10 (Forecaster Mike Natoli - College Park, Maryland) When a schoolboy asked this key question of patrol officer John Blake in The Dark Knight Rises, it captured the essence of a foremost question on the minds of many in the audience. 

Are you searching for a sign of what lies ahead this winter? Wondering if there are any clues that might support or reject the forecasts for big snowstorms in some parts of the country this upcoming season? If you're a Powderhound, in public safety, or just want to know what's really going on with the winter forecast, the answers to our uncertainty may rest with the "He" of our movie analogy. 

In our take-off analogy of the Batman story, "You" are the curious schoolboy, our Long Range Forecasters play the role of Officer Blake, and the "He" is simply El Nino. This the world-reknowned Spanish term for the Christ child, so applied to climatology due to the tendency of this sea-surface temperature driven oceanic influence to peak around the Christmas holiday season off the coast of Peru.  An El Nino condition in this region is characterized by warmer than normal temperatures across the equatorial Pacific Ocean. 

The top map shows the Sea Surface Temperature Anomalies on 10/07/2002, heading for the eventual moderate  El Nino of the 2002-03 winter. Compare to the bottom map, which shows the current state of a virtually non-existent El Nino as of 10/08/2012. Image Credit - NOAA

The last time a defined "moderate"  El Nino formed was from Fall 2009 into Spring 2010. During the winters of ’10-’11 and ’11-’12, the opposite effect of El Nino was observed, in which below normal temperatures took place in this region. This cooling trend is denoted in Spanish as La Nina, for the sister. 

WHERE DOES THE DATA STAND? Since the spring, long-range climate models have been pointing to El Nino forming for the upcoming winter. The only problem is that the majority of these models showed El Nino developing by August or at least September. However, here we stand at October 10th, and El Nino has yet to form. 

  • As of October 9th, the ENSO index stands at 0.1º C above normal'
  • This reading is still below the threshold for El Nino conditions of 0.5º C. 
  • Above normal anomalies in all 4 regions have decreased in the last few weeks instead of increasing as would be expected heading into an El Nino year. 
This is in the most important Nino 3.4 region which is shown on the map below. 

The top shows the locations for each of the four Nino regions, and the four graphs below show the Sea Surface Temperature Anomalies for the last year in each of the four regions. 
Image Credit - NOAA Climate Prediction Center (CPC)

PEACEMAKER OR PREMONITION? In addition to the warmer than normal temperatures, El Nino also has an impact with temperature and precipitation patterns across the Pacific which in turn affect the United States. For example, El Nino conditions are often characterized by westerly anomalies , or weaker than normal easterly trade winds. 

  • In the month of September, we saw weak westerly anomalies start to form in the western and central Pacific which is a sign of El Nino. However, the difference is very slight, and atmospheric circulation is still close to normal. 
  • The graphic below shows wind anomalies near the equator for the last several months along different longitudes. The reds indicate westerly anomalies while the blues show easterly anomalies.
As one can see, westerly anomalies (the ones typically characteristic of El Nino conditions) have expanded and strengthened to the west of 180º Longitude (The International Date Line). This actually does indicate a slight trend to El Nino instead of stronger easterly anomalies that come with the opposite, La Nina. 

Wind Anomalies near the equator for the last several months from the CPC

SO...WHAT ABOUT THE WINTER? If these westerly anomalies were to strengthen or expand eastward, a weak El Nino could still develop. On the other hand, we have the near average equatorial temperature, with significant drops in temperature over the last few weeks. However, many long-range climate models are showing little to no El Nino forming, while the Climate Prediction Center has reduced the probability to a 55% chance of El Nino conditions developing. 

Just like the Dark Knight comes to save Gotham, many Powderhounds look for El Nino to save the winter forecast, or at least create some alternate reality in which big snows are still possible. The influence of shorter-term signals, such as the North Atlantic Oscillation also carry an influence on large scale regional patterns, and that will be examined in a future article later this month. For now, the reality remains clear: Although  El Nino may be the hero the winter forecast deserves, but not the one it needs right now.  

Lead Author: Forecaster Mike Natoli

EditorCEO Rich Foot
Forecasters Jason Mitchell, Jason Isaacs, Wesley Hicks

No comments: