01:04 El Nino, La Nina And Tornadoes A long-range seasonal prediction of severe thunderstorm activity can be gathered from changes in El Nino-La Nina cycles months in advance. Matt Sampson has the details.

One of the strongest El Niños on record is now weakening quickly, and may shift to its opposite, La Niña by this fall, according to a recent government outlook.

After tying the record for the strongest El Niño, as defined by a three-month running mean sea-surface temperature anomaly in the so-called Niño 3.4 region of the central and eastern equatorial Pacific Ocean, sea-surface temperatures are steadily cooling.

(MORE: El Niño 2015-2016 Ties a Record )

Weekly sea-surface temperature (SST) anomalies, which peaked Nov. 18 at 3.1 degrees Celsius above average, have now dropped to 1.7 degrees above average as of March 16, values last seen in late July, according to NOAA's Climate Prediction Center.

You can see this in recent SST animations, illustrating nicely the peak coverage of large warm anomalies during the northern hemisphere's late fall and early winter, followed by a steady decline of the largest anomalies later in February and March.

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/sst-animation-dec-mar2016-noaa.gif" srcset="https://s.w-x.co/sst-animation-dec-mar2016-noaa.gif 400w, https://s.w-x.co/sst-animation-dec-mar2016-noaa.gif 800w" > Weekly sea-surface temperature anomalies from late December 2015 through mid-March 2016. Equatorial Pacific warm anomalies indicative of the strong El Niño of 2015-2016 is highlighted by the red box. (NOAA/ESRL/PSD) (NOAA/ESRL/PSD)

Looking below the surface, you can also see a trend of colder-than-average water working its way eastward across the International Date Line, eating away at the warmer-than-average equatorial Pacific water from below, another sign of El Niño's weakening.

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/sst-depth-anomalies-midmarch2016.gif" srcset="https://s.w-x.co/sst-depth-anomalies-midmarch2016.gif 400w, https://s.w-x.co/sst-depth-anomalies-midmarch2016.gif 800w" > Tropical Pacific temperature anomalies from the surface to a depth of about 450 meters from Jan. 13 through Mar. 14, 2016. (NOAA/CPC) (NOAA/CPC)

NOAA's March El Niño outlook suggests this El Niño may be all but gone by late spring and early summer.

In fact, the majority of model forecasts suggest the equatorial waters may become cooler than average this summer, potentially even swinging into La Niña as early as this fall.

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/enso-forecasts-midmarch2016.jpg" srcset="https://s.w-x.co/enso-forecasts-midmarch2016.jpg 400w, https://s.w-x.co/enso-forecasts-midmarch2016.jpg 800w" > ENSO plume forecasts in mid-March 2016. (NOAA/CPC, IRI, Columbia University) (NOAA/CPC, IRI, Columbia University)

El Niño and La Niña events typically only last for 9-12 months, and typically recur again every 2-7 years, according to Columbia University's International Research Institute for Climate and Society.

Flip-flops from a strong El Niño to La Niña are not unusual.

Following the record strong El Niño of 1997-98, La Niña almost immediately set in the following summer, reaching moderate-to-strong intensity before finally ending in spring 2001.

A similar thing happened following the strong El Niño of 1972-73.

However, neutral conditions followed three other strong El Niños of 1982-83, 1965-66 and 1957-58.

What Does It All Mean?

Summer 2016

There are some broad trends that have shown up in past weakening El Niño events that could give a hint on what to expect this summer.

(MORE: Summer Outlook 2016 )

"If we look at rapidly decaying historical ENSO events (trends, instead of actual values), we see that the summer heat is centered in the northern Plains into the Great Lakes states," said Dr. Todd Crawford, chief meteorologist at The Weather Company's energy division.

<img class="styles__noscript__2rw2y" src="https://dsx.weather.com//util/image/w/wsi_summer.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0" srcset="https://dsx.weather.com//util/image/w/wsi_summer.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 400w, https://dsx.weather.com//util/image/w/wsi_summer.jpg?v=ap&w=980&h=551&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 800w" > A summer 2016 temperature outlook, issued in mid-March 2016, by The Weather Company Professional Division.

Atlantic Hurricane Season 2016

As we wrote in early January, strengthening El Niños during the Atlantic hurricane season tend to yield stronger wind shear, which tends to either tear apart developing or mature tropical cyclones.

Sure enough, June through October 2015 Caribbean wind shear was the highest on record dating to 1979, according to Dr. Phil Klotzbach, tropical scientist at Colorado State University.

Klotzbach also found that the chance of a U.S. hurricane impact rises dramatically in a La Niña or neutral (neither El Niño or La Niña) season compared to an El Niño season.

With El Niño potentially vanishing by the start of the 2016 season, it at least loads the dice toward an increased chance of tropical cyclones surviving into the Caribbean Sea, or forming there, particularly later in the season as El Niño disappears farther in the rear-view mirror.

If El Niño was the only factor, that is.

The odds may shift a bit toward a more active Atlantic hurricane season in 2016, but El Niño's absence doesn't guarantee that outcome.

Nor does it mean it poses any greater threat to the U.S. compared to any other year, as landfalls tend to be poorly correlated with numbers of named storms.

Winter 2016-2017

We've said many times an El Niño, La Niña, or the lack of either, known as the neutral phase, is only one large-scale forcing on the atmosphere. It is not the be-all and end-all determining whether a season is wet, dry, cold or warm.

Despite that, the peak atmospheric reponse to the equatorial Pacific anomalies tends to occur in the northern hemisphere winter months.

So, in the event we have a La Niña settling in by fall or winter, let's take a look at December-February U.S. temperature and precipitation anomalies during weak (SST anomalies from 0.5 to 0.9 degrees below average), moderate (1.0 to 1.4 degrees below average) and strong (1.5 degrees below average or cooler) La Niñas.

Temperatures

While there are some differences among La Niña magnitudes, some commonalities emerge regarding La Niña winter forcing in the U.S.:

Cold: Northern Plains, Upper Midwest, New England, New York state, West Coast

Northern Plains, Upper Midwest, New England, New York state, West Coast Warm: Southern Plains, Southeast

Neglecting other factors, it appears the stronger the La Niña, the stronger the likelihood the winter warmth spreads farther north into the Corn Belt, Ohio Valley and Mid-Atlantic states.

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/la-nina-djf-temps-anomalies.gif" srcset="https://s.w-x.co/la-nina-djf-temps-anomalies.gif 400w, https://s.w-x.co/la-nina-djf-temps-anomalies.gif 800w" > December-February temperature anomalies (degrees Fahrenheit) during 11 weak, 6 moderate, and 3 strong La Niña events dating to 1950, using the classification scheme from Jan Null. (NOAA/ESRL PSD and CIRES-CU) (NOAA/ESRL PSD and CIRES-CU)

Precipitation

Again, despite some differences among La Niña magnitudes, some commonalities are apparent:

Wet: Pacific Northwest, Biterroots (western Montana/Idaho), parts of the Ohio Valley, Tennessee Valley

Pacific Northwest, Biterroots (western Montana/Idaho), parts of the Ohio Valley, Tennessee Valley Dry: Southern Plains, Gulf/Southeast coast including Florida, Southern California, Desert Southwest

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/la-nina-djf-precip-anomalies.gif" srcset="https://s.w-x.co/la-nina-djf-precip-anomalies.gif 400w, https://s.w-x.co/la-nina-djf-precip-anomalies.gif 800w" > December-February precipitation anomalies (inches) during 11 weak, 6 moderate, and 3 strong La Niña events dating to 1950, using the classification scheme from Jan Null. (NOAA/ESRL PSD and CIRES-CU) (NOAA/ESRL PSD and CIRES-CU)

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