At a Glance

Temperatures may be warmer than average overall in the western and northern states.The South could be wet but areas the Canadian border might be dry.El Niño may play a role in the weather conditions this winter.

Winter 2018-19 could bring above-average temperatures to the northern and western United States, and it's likely that parts of the South and East will see wetter-than-average conditions, according to an outlook released Thursday byNOAA.

A weak El Niño event is expected to develop this winter, and that could have someinfluence onlarge-scale weather patterns.Last week, NOAA saidthere's a forming later this fall and lasting through winter 2018-19 (December through February).

“Although a weak El Niño is expected, it may still influence the winter season by bringing wetter conditions across the southern U.S., and warmer, drier conditions to parts of the North,"said Mike Halpert, deputy director of NOAA’s Climate Prediction Center, in a press release.

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La Niña, El Niño, or the lack of either, known as the neutral phase, is only one large-scale forcing on the atmosphere. It is not the sole factor in determining whether a season is wet, dry, cold or warm. Other factors are in play such as the Arctic Oscillationand the, and their influence can't be predicted months into the future.

Temperature Outlook

The forecast for this winter – December, January and February –has the highest odds of above-average temperatures from the western U.S. to the northern Plains, Great Lakes and New England.

El Niño winters typically result in across a large chunk of those regions, including the Pacific Northwest, northern Plains, upper Midwest and northern Great Lakes. This does not mean there won't be any bouts of frigid cold in the northern climates; rather, the overall temperatures for the three-month period are favored to be above average.

Overall temperature outlook for December through February.

(NOAA)

NOAA says much of the Ohio Valley, Southeast and mid-Atlantic have an equal chance of seeing above-, below- or near-average temperatures this winterdue to uncertainty in both the long-range forecast guidance and any shorter-term weather pattern influences that develop in mid-winter.

One factor in this uncertainty is the previously mentioned Arctic Oscillation (AO), which plays a role in determining how many plunges of arctic air push all the way into the Deep South. If the AO is in its favorable phase for allowing arctic air masses to slide southward, it could resultin prolonged spells of below-average temperatures in the East, NOAA says.

Precipitation Outlook

A swath from the southern Rockies to the Gulf Coast states and mid-Atlantic has the largest signal of above-average precipitation this winter.

El Niño winters typically feature across the southern tier of the U.S.

If any cold air meets up with the enhanced precipitation chances in those regions, it could result in bouts of snow, sleet or freezing rain.

Overall precipitation outlook for December through February.

(NOAA)

Meanwhile, parts of the northern Rockies, northern High Plains and Great Lakes could be in for a drier-than-average winter overall.

On the West Coast, the Madden-Julian Oscillation (MJO) might play a role in fueling heavy rain and snow events this winter, particularly since El Niño is forecast to be weak, NOAA says. But the MJO's influence cannot be predicted far in advance.

Keep in mind, these outlooks are overall trends over a three-month period from December through February.

An individual cold front or an upper ridge of high pressure can lead to a period of colder or warmer weather, respectively, that bucks the overall three-month trend. The same front or area of high pressure can bring a brief period of enhanced precipitation or dry spell that may or may not be indicative of the overall trendforecast.

What is ElNiño?

El Niño, the periodic warmingof the equatorial eastern and central Pacific Ocean, can shift weather patterns over a period of months, bringing the possibility of more sustained warm, cold, wet or dry weather in parts of the world.

Sea-surface temperatures in the equatorialPacific Ocean have been running above average recently, which is why NOAA is forecasting the potential for weak El Niño conditions to develop later this fall or winter.

The black box highlights the warming water in the equatorial Pacific Ocean early August into early October.

(NOAA)

The peak atmospheric response to the equatorial Pacific anomalies tends to occur in the Northern Hemisphere's winter months. This is why the possible development of El Niño or its counterpartLa Niñareceives a large amount of attention prior to winter.