What is La Niña weather? What is a La Niña winter? What does it mean for Central Texas?

National Weather Service forecasters last week heralded the return of La Niña and that "La Niña winters tend to be drier and warmer across the southern third of the U.S." But you might still be wondering who is La Niña and why is she affecting our weather? So here are five things to know about La Niña and its effect on Central Texas:

1. La Niña is not a storm.

La Niña and its counterpart, El Niño, aren't storms or weather events that affect a specific area at a specific time, according to the National Weather Service. Stronger than normal winds in the Pacific Ocean can lead to cooler tropical waters, which then affect atmospheric circulation around the world.

"Think of how a big construction project across town can change the flow of traffic near your house, with people being re-routed, side roads taking more traffic, and normal exits and on-ramps closed," the weather service explains on its website. "You would feel the effects of the construction project through its changes to normal patterns, but you wouldn’t expect the construction project to 'hit' your house."

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2. Pacific Ocean temperatures can affect Texas weather.

When you hear forecasters talk about La Niña, they’re referring to the cooling of sea temperatures in the equatorial waters of the eastern Pacific Ocean. During a La Niña event, the cooler-than-normal ocean influences the pattern of the jet stream, a river of air that can corral or unleash cold air masses from the north.

The combination of these factors can affect weather in Texas. El Niño can mean wetter, cooler seasons for us, but a La Niña at this time of year typically leaves Texas drier and warmer than normal.

Last year, we experienced one of the warmest and driest autumns, thanks to La Niña. Austin recorded its 19th-warmest fall season — the calendar months of September, October and November — with an average temperature of 72.1 degrees, or about 2 degrees above normal.

The year also gave us the city's second-warmest November, with an average temperature of 66.3 degrees — a full 5 degrees above normal.

3. Austin has had signs of an emerging La Niña.

A drier-than-normal September generated only 1.79 inches of rain in a month that sees on average around 3.45 inches, according to readings at Austin’s main weather station at Camp Mabry.

October — a month that normally delivers about 3.91 inches of rainfall to Austin — has already produced 4.54 inches of rain, but about 64% of that total arrived over just two days, Oct. 13-14.

Austin’s autumn temperatures have been warmer than normal, too. The average temperature for September was 82.9 degrees, or about 2.1 degrees than normal. The month was tied for the city's eighth-warmest September on record.

Meanwhile, Austin's average temperature for October (through Oct. 22), is about 73.4 degrees, according to weather service climate data from the past 30 years. But this year, the average temperature in October as of Friday was 75.1 degrees or 1.7 warmer than normal.

That average could climb higher if the weather service's extended forecast holds up and we see temperatures as high as 91 on Monday and Tuesday.

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4. Austin's winter will be warmer and drier than normal.

The local National Weather Service forecasters based in New Braunfels also expects the winter to follow suit.

"La Niña conditions have developed in the Pacific and are expected to continue with an 87% chance of La Niña in December 2021 to February 2022," the weather service posted on Facebook on last week. "This typically leads to conditions through winter that are, on average, warmer and drier than normal here in South-Central Texas."

Forecasters warned that a La Niña winter doesn't rule out wintry weather in our region or guarantee it.

"It also doesn't mean that every corner of South-Central Texas will be warm and dry this winter," they wrote. "But, the odds are certainly tilted in the direction of a warmer, drier fall into winter similar to last year (at least up until mid-February; we are unlikely to see conditions that cold and icy/snowy again this year)."

5. Drought conditions could worsen.

The Interstate 35 corridor and parts of the Hill Country west of the metro area were drought-free as of Oct. 19, the latest U.S. Drought Monitor data show, largely because of the short but heavy doses of rain the region received over the summer and from the brief but productive storms earlier this month.

But compared to a month ago, Texas drought conditions have intensified in East Texas and the Panhandle.

The National Weather Service's annual winter outlook released Thursday warned that La Niña could mean an expansion of drought conditions.

“Consistent with typical La Niña conditions during winter months, we anticipate below-normal temperatures along portions of the northern tier of the U.S. while much of the South experiences above-normal temperatures,” said Jon Gottschalck at the national Climate Prediction Center. “The Southwest will certainly remain a region of concern as we anticipate below-normal precipitation where drought conditions continue in most areas.”