ENSO Update: La Niña officially ends

LaNina2011to2012

RICHMOND, Va. (WTVR) – The cooling of the equatorial Pacific waters west of South America likely aided our mild Winter in the Mid-Atlantic, keeping the jet stream pattern over the U.S. northwest of Virginia most of the season. In the latest update from the Climate Prediction Center, scientists monitoring the El Niño Southern Oscillation concluded, “La Niña has transitioned to ENSO-neutral conditions, which are expected to continue through northern summer 2012.” You can see La Niña depicted on this plot from Summer 2011 through April 2012 in blue on the plot here:

Plot: Climate Prediction Center

Plot: Climate Prediction Center

Here’s what an “average” La Niña Winter looks like:

The warmer-than-average and drier-than-average part certainly verified for the Southeast U.S. into Virginia this Winter.
BLOG BONUS: Click here for more on our record-warm 2012 so far in the U.S. And click here for more on Winter, specifically, which is when La Niña’s impacts are most noticeable in North America.

So what do ENSO-neutral conditions mean for us into this Summer? Well, not that much, really. We can expect “business as usual” for the Summer, with more temporary weather patterns impacting local extremes.  Considering our recent trend of warmer-than-average weather, we’ll likely still be warmer-than-average into this Summer. That doesn’t necessarily mean we’re in for a major heat wave, as those are also driven by prolonged stretches of stagnant weather patterns (like a broad ridge parked for a week or more over us).

Forecast models that extend months out indicate no return of La Niña this year. The CPC says, “A majority of models predict ENSO-neutral conditions to continue from April-June (AMJ) through the June-August (JJA) season.”

ENSO forecasters go on to say, “However, at least half of the dynamical models predict development of El Niño conditions by JJA. Still, from JJA onward there is considerable forecast uncertainty as to whether ENSO-neutral or El Niño conditions will prevail, due largely to the inability to predict whether the warmer SST will result in the ocean-atmosphere coupling required for a sustained El Niño event. The official forecast calls for ENSO-neutral conditions through JAS, followed by approximately equal chances of Neutral or El Niño conditions for the remainder of the year (see CPC/IRI consensus forecast).”

Meteorologist Carrie Rose
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