Warmer Weather, or Not

It's Almost Groundhog Day. Is Winter Gone With the Wind?

Emily Jerison, left, and Rachel Matheson play by a pool Jan. 6 in Bethesda. (By Melina Mara -- The Washington Post)

What a weird winter!

Now it's really cold outside. But remember a few weeks ago when it was so warm that everybody was wondering whether winter would ever come?

And tomorrow is Groundhog Day. About 7:25 in the morning, Punxsutawney Phil, the most famous groundhog in the world, will come out of his burrow on Gobbler's Knob in Pennsylvania, and predict whether there will be an early spring. As legend has it, if Phil sees his shadow and goes back in his burrow, we're in for six more weeks of winter.

But nothing has been certain this year.

Think back to December, which was the fourth-warmest December on record in the United States. In Washington, 23 days that month were warmer than usual, including a balmy 75 degrees on Dec. 1, according to the National Weather Service.

What's not to like about that?

Well, some people worry that this unusual weather is caused by global warming, the gradual rising of the temperature of the atmosphere around the world. Global warming is caused by gases that hold on to heat released into the atmosphere by our cars and electric power plants, among other things. These gases are called greenhouse gases because they act like a glass greenhouse that keeps plants warm, even in winter.

Other people think that the warmer temperatures are the result of a weather pattern called El Ni?o, which means "the child" in Spanish. (It got that name because it often shows up around Christmas, the birthday of the Christ child.)

An El Ni?o pattern happens when the winds stop blowing west from South America toward Indonesia. Warmer water currents in the Pacific Ocean then heat the air near the equator. That changes the path of the jet stream -- winds that blow high above Earth. Instead of the jet stream bringing cold air from the Arctic or Siberia into the United States, as it normally does in winter, it brings warmer air from the Pacific.

The ocean temperature doesn't have to warm up much to make a big difference in our weather. Going up just 2 to 4 degrees can change weather around the world.

Vernon Kousky is a research meteorologist with the government's Climate Prediction Center. He says there is no one answer for what's causing our warm winter: "You just can't blame everything on El Ni?o, or on global warming either."

While global warming has raised the average world temperature 1 to 2 degrees over the last 30 years, Kousky said, it hasn't necessarily caused the current warm winter. The same is true for an El Ni?o, he said. While the water temperature in the Pacific is warmer, an El Ni?o usually means warm weather through the whole winter.

What we're having "is just typical winter weather," Kousky said. And it's always changing, so don't get too used to it.

While you were playing outside in the warm sun not too long ago, he noted, "they had snow in Arizona and Southern California."

To learn more about our weather, go to http://www.education.noaa.gov/students.html.

-- Ellen Edwards