It’s hard to remember, but last winter was the warmest on record in the continental U.S. This winter might go the other way.

Actually, this winter could be very cold and very wet in parts of America. There’s a La Niña threatening to spoil T-shirt-in-December weather. You remember La Niña, right? It’s the Debbie Downer sister to El Niño.

• The Climate Prediction Center (per CNN) says there’s a 60 percent chance of La Niña this winter.
• Once it arrives (or if it arrives) in November, it’ll stick around until March.
• This isn’t all that bad of news if you live in Southern states, but if you live in the midwest, northwest and north-central planes, it could be ugly.

What Is La Niña?

The National Oceanic and Atmospheric Administration describes La Niña as a weather pattern that begins with cooler-than-normal sea surface temps in parts of the Pacific. The cold waters push the jet stream further north, which results in a concentration of cool air and precipitation in states north of the Kentucky/Tennessee border.

Related: 5 Things Your Grocery Store Isn’t Telling You

The jet stream enters the U.S. at an angle, so Nevada, California, Utah and Colorado are mostly south of it, meaning suntans in December.

Broadly speaking, during La Niña, winters are warmer and drier in the south and colder and wetter in the north. Heavy flooding is one possible side effect of La Niña. It can also lead to a more severe hurricane season.

The good news is that every La Niña is different, and this one is not expected to be as strong as others. In fact, you don’t have to go back far for a comparable example.

When Was the Last La Niña?

A rare triple-dip La Niña plagued America from 2020 to 2023, as if we didn’t have enough to worry about. The first two years of that pattern are classified as “Moderate” by the Golden Gate Weather Service, and 2023 was labeled “Weak.”

The last strong La Niña came in 2010-11. That one was a beast, with the coldest and wettest winters in recent years occurring throughout the northeast, midwest, west and Pacific northwest. Chicago shut down after a Groundhog Day blizzard, and the spring included record tornado activity. There was also heavy flooding along the Mississippi River.

What Is El Niño?

El Niño is the opposite of La Niña in that warmer-than-normal air pushes the jet stream south, leading to warmer temperates across the northern U.S. and Canada. Last year’s El Niño is labeled as “strong” on the “weak to very strong” scale used by the GGWS. We seem to have one or the other most years.

Since 2000, either La Niña or El Niño have come knocking just five times.

Bottom line, buy a new snow shovel and sled now, and don’t complain if you actually do get a white Christmas this year. The bill has come due after a very pleasant winter we all forgot about last year.