Ask any weather forecaster around, and many will agree that winter weather is not only one of the trickiest to forecast but the most-asked about forecast. Perhaps it’s Christmas in July that sparks people’s curiosity about the upcoming winter season?

Either way, winter weather is often dictated by El Niño or La Niña.

The good news is thanks to advancing technology, research, and education, meteorologists are able to provide better and earlier winter outlooks especially in the last decade. However, fall is still too early!

It’s important to note that winter weather outlooks are not forecasts by any means. So you can not predict seven inches of snow on this exact date in February several months out.

However, meteorologists can provide information usually 2-3 months out if winter could be warmer or cooler than average, and if precipitation looks above or below average, including snowfall in your area.

When researching winter weather outlooks, meteorologists look at a variety of global climate factors like ocean water temperatures. It might seem strange, but ocean water temperatures play a major role in predicting the winter weather season in the United States!

According to the National Ocean and Atmospheric Administration (NOAA) there are two major compact weather patterns that result from variations in ocean temperatures in the equatorial Pacific. There are two opposite phases in the El Niño-Southern Oscillation (ENSO) cycle called El Niño and La Niña.

These episodes usually last from 9 to 12 months, but some have lasted up to 18 months. 

You may have heard about these terms before but let’s dive deep into the El Niño and La Niña ocean cycles and how each can impact a winter prediction.

In Spanish, this term means ‘The Little Boy’. It is also known as the ‘warm’ phase of the ENSO.

NOAA refers to the term El Niño as the large-scale ocean-atmosphere climate interaction linked to a periodic warming in sea-surface temperatures across central and east-central equatorial Pacific. 

The formation of an El Niño can mean significant changes for the weather around the world, as well as the United States. In North America, the effects from El Niño usually occur during the upcoming winter season.

During a typical El Niño, the storm track will shift farther south as the jet stream splits creating a secondary jet stream known as the subtropical jet stream. This tends to bring more rainfall and storms to California and throughout southwestern US. 

The subtropical jet extends an active pattern also into southeastern US, which brings that region more tropical moisture. And the winter pattern is usually wet in that region, but it can be cooler than average.

As the south half of the country soaks up wetter-than-average winters, the northern half sees less activity, including snowfall. Across the upper Great Plains and throughout the Great Lakes region it tends to be milder with less snow. The split in the jet stream causes a large ridge that extends further north into Canada, so this is typically why it is milder than normal and less snowfall.

While there is a ridge over the north-central half of the country, the northern jet streams sinks back south in New England. Across the northeastern US, just like areas to the south, the jet stream becomes a storm track for winter storms. Along with more activity, it also remains milder than normal.

Again, it's worth noting that every El Niño varies as well as the intensity. We experience a range of weak, moderate and strong El Niños that can last from a few months to up to a year and a half long.

El Niño is the opposite of La Niña, which in Spanish translates to ‘The Little Girl’. It's the ‘cold’ phase out the the ENSO.

NOAA explains that La Niña episodes represent periods of below-average sea-surface temperatures across the east-central equatorial Pacific, and its impacts are opposite.

Unlike the El Niño, the La Niña typically doesn’t create the jet stream to split. Instead, it’s all about the strong polar jet stream.

The setup that is usually seen with La Niña is an area of high pressure over the northern Pacific Ocean, just south of Alaska’s coast. This high pressure system creates a blocking pattern and a strong ridge.

The typical flow of the polar jet dives south of the northwestern edge of the country, which tends to lead to an active winter. The pattern is wetter than normal. 

There is also a large cold airmass that spills into the northern Great Plains from Canada as a result of the polar jet stream setting up further south. This usually brings in more systems throughout the winter.

Following the flow of a classic La Niña polar jet eastward, it tracks over the Ohio Valley and up through New England. Just like the Northwest, these regions usually are wetter-than-average during the winter, which could also mean more snow.

It’s usually a different scenario for the southern half of the United States during a La Niña. Again, opposite of El Niño, their winters tend to be drier-than-average due to no subtropical jet influence or not as strong. Plus, it’s not uncommon to see warmer winter temperatures, especially in the southeastern US.

Every La Niña phase is somewhat different as each event can have different intensities ranging from weak, moderate and strong.

When neither El Niño nor La Niña aren’t present then we are in a neutral pattern. 

During this pattern, tropical Pacific sea-surface temperatures are usually close to average. However, this does not mean that weather conditions will be necessarily average.

In turn, it can actually make the winter outlook or forecasts more difficult to predict several months out. It also allows for other atmospheric forces to impact the winter pattern, such as the Arctic Oscillation. 

On average, colder-than-average temperatures in the Midwest and Northeast emerge during a neutral winter because the jet stream will shift further south. Areas further to the south half often end up warmer-than-average. 

The subtropical jet stream may also shift and can be a bit of a wild card, as it depends on the location of the polar jet. Storms usually track into the northwestern US as opposed to California, which often brings drier conditions in California, but wetter conditions in southeastern US.

Due to the jet stream set up, regions like the Northeast and northern Rockies also typically trend wetter-than-average. 

Most of the US during the December-through-February period experiences chillier-than-average temperatures.

The El Niño-Southern Oscillation is key to forecasting winter weather outlooks. The different phases can influence the overall trend for the upcoming winter season in the US as well as weather across the planet. 

Each episode is different, ranging from the intensity to how long it lasts. Typically, more extreme weather events like floods or droughts occur during a La Niña or El Niño. 

Keep in mind these are patterns and we still have individual storm systems and fronts that will deviate from these outlooks at times.