Las Vegas Sun

October 23, 2017

Currently: 60° — Complete forecast

Shiver now, for this summer comes the sizzle

The more sensitive among you might have noticed something about the weather.

No, not that we're in a cold snap. We know that. And we've heard that Sunday's high temperature was a record setter for being so low on that date - reaching only 39 degrees at the day's warmest point.

No, that's not the news.

The news is that, record-breaking cold temperatures in Las Vegas notwithstanding, the nation's average annual temperature is slowly increasing - further evidence, some scientists say, of global warming.

And we're feeling that warming here. According to the National Weather Service, last year was the third-warmest year on record for average temperatures in Las Vegas.

Our mix of hot and cold could continue through summer, when federal scientists are predicting scorching heat for the desert Southwest. That's an option that might sound appealing to those shivering through subfreezing nights and taking pictures of the frozen water fountains.

Nationally, a lingering wave of warm air over the East Coast propelled 2006 to the warmest year ever for the continental United States. The average temperature was more than 2 degrees above the 20th-century average.

Jeffrey Masters, meteorology director for Weather Underground, one of the Internet's first weather forecasting and analysis sites, says there are three factors that contributed to last year's record warmth: global warming, normal variability and the phenomenon known as El Nino - a patch of warmer-than-usual water in the central Pacific that affects weather patterns throughout North America and the world.

He notes that 1998 had a similar pattern of warming, and that year also was an El Nino year. But even for El Nino events, December was weird.

From Dec. 7 to Jan. 7, the average temperature across the continental United States was 14 degrees above normal. Masters says the only comparable record he can think of is January 2006, when the month was 10 degrees above normal.

He believes that two exceptional years in a row is evidence of global warming, which most scientists believe is a product of the burning of fossil fuels adding greenhouse gases to the atmosphere.

"One winter, I could (explain it as) natural variability," Masters says. "Two in a row, you've got to put climate change into the picture."

Kelly Redmond, regional climatologist with the Desert Research Institute's Western Regional Climate Center in Reno, says he sees the same evidence. Global warming is a factor, but he scratches his head when it comes to El Nino, which appears to be declining in strength.

"We haven't seen a lot of climate things over the winter that we can strongly subscribe to being from El Nino," Redmond says. "It has kind of been a mystery why it has worked out this way."

Usually, El Nino means that there will be more precipitation in the Southwest, less in the Northwest, but so far this winter it has been the opposite, he says.

"Nobody that I've talked to has given us any good reason why it has been different," he says.

Redmond and other meteorologists say that phenomenon such as El Nino and its sister event, the ocean cooling called La Nina, still have to be studied in detail, and that even small variations in the size and distribution of the ocean temperature anomalies can mean a big difference in North American weather.

He says the prediction from the National Atmospheric and Oceanic Administration of above-average temperatures next summer for Las Vegas is based on long-term trends.

"What's basically behind those maps - the reason they are warm is because it was warm last year," Redmond says. "There has been a trend. The smart money is on betting that the trends will continue."

Summer is still a long way away and those predictions could change, he cautions. El Nino, although weakening, is still likely to play a role in determining the weather over the next three months. Beyond that, it gets harder to predict.

Redmond says it is important for people to understand that the long-term trends will mean higher temperatures for the Southwest - indeed, for the planet - but that doesn't mean that we won't have cold spells like this week's in Las Vegas.

"As the climate warms up, we don't expect to stop seeing events like this one," he says. "The fact that it is generally warming up doesn't preclude cold episodes."