El Nino becomes La Nina and what it means for Alaska

 Typical La Nina wintertime pattern.  <br />Courtesy NWS/NCEP Climate Prediction Center
Typical La Nina wintertime pattern. <br />Courtesy NWS/NCEP Climate Prediction Center (KTUU)
Published: Jul. 7, 2016 at 3:33 PM AKDT
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This past winter we experienced one of the strongest El Nino events on record. Beginning in June 2016, we began shifting into a “neutral” phase but scientists forecast we’ll move through neutral and into “La Nina” by fall through the winter. According to the National Weather Service, there is a 75 percent chance of La Nina during the fall and winter of 2016-17.

A couple of quick definitions. El Nino is characterized by prolonged warmer than normal sea surface temperatures at the equator. La Nina is the opposite. Sea surface temperatures are cooler than normal for an extended period. Check below for a more technical description of El Nino/La Nina.

Despite being so far away from the equator, El Nino and La Nina can impact Alaska.

“La Nina winters for Alaska over much of the state are much more likely to be significantly cooler than normal especially compared to El Niño events, such as we just coming out of,” says Rick Thoman, NWS Climate Sciences and Services Manager for the Alaska Region.

Now, a little caution before there’s too much excitement for a cold, snowy winter. The ocean temperatures off the southern coast of the state—particularly from Kodiak eastward—remain well above normal. Those warm ocean temperatures were one of the elements that kept southern Alaska warm through last winter. And that warmth isn’t going to move out quickly.

“That warm water is not just at the surface,” says Thoman. “It extends down into the water column quite a bit and the heat anomaly is quite substantial and that's going to take a long to time work that out.”

As for precipitation during a La Nina winter, there isn’t a consistent pattern of wetter or drier for most of the state with the exception of the Panhandle. Southeast tends toward drier than normal conditions during La Nina winters.

“During La Nina’s, we often end up with a high pressure aloft over western Alaska or the Bering Sea,” says Thoman. “And that’s not conducive for a storm track into Southeast.”

The forecast for this year’s anticipated event is a moderate La Nina. Strong La Ninas rarely follow strong El Ninos.

The El Nino/Southern Oscillation—or ENSO—is a periodic change in winds and sea surface temperatures in the equatorial Pacific ocean. An “El Nino” event is declared when the average sea surface temperature in the equatorial Pacific is at least 0.5C degrees warmer than normal over a three-month period. “La Nina” is the opposite. Sea surface temperatures must be at least 0.5C degrees cooler than average in the equatorial Pacific.

Some fun La Nina—and El Nino—facts:

- There have 14 La Nina events since 1950—when these records began. There have been 23 El Nino events during that same time period.

- Like El Nino, La Nina tends to peak in the late fall/early winter.

- All 14 La Nina events have begun within two years of an El Nino.

- La Nina events often last longer than El Nino, but La Nina tends to be less extreme than El Nino. One La Nina event lasted for 33 months, through three winters.