Pacific water fight sets weather tone

Storms, flooding and tornadoes that have plagued Southern Nevada this year may return next year, 20 years after a January snowfall pounded the Las Vegas Valley with more than 7 inches.

Or, it may be a normal, sunny winter and the weather will become predictably the same again -- bright and hot.

It depends on the weather winner in the battle between the hot and cold waters of the Pacific Ocean.

El Nino, the warm water that has affected weather along the west coasts of North and South America this year, is jousting with cooler water known as La Nina, according to the latest observations from NASA's Topex-Poseidon satellite.

The ocean currents are running both hot and cold.

While both signals are strong, no one is sure which will dominate the ocean in the coming year, according to meteorologist Ron McQueen at the National Weather Service in Las Vegas.

El Nino, "the boy," appears around Christmas off the coast of Peru. Peruvian fishermen noticed schools of fish heading north when the warmer water moved into shore. They thought of the Christ child and thus the name.

This year's El Nino is so large and strong that the jet stream (high-speed winds at altitude) controlling the West's weather has teamed up with the East Coast jet stream, helping storms pound California and Southern Nevada, McQueen explained.

"It's just a remnant of the largest El Nino this century clinging to the equator near Mexico and South America," McQueen said. "It won't give up easily."

La Nina, "the girl," is essentially the opposite of El Nino. It is cold water that extends along the coast of South America and into the central Pacific. During a La Nina, the Southwest tends to dry out, producing fewer storms, McQueen said.

Both ocean-based events are linked to changes in global weather patterns where winds, ocean currents and moisture interact.

Summers during La Ninas tend to be hotter and drier than this one. Fewer storms are expected.

But it's the winters that are so much more different during a La Nina.

Southern Nevada has an excellent chance of snow blanketing the valley during La Nina phases, McQueen said.

Meteorologist Scott Cordero, who works with McQueen, did a historical study of snowstorms.

The last big snowfall came on Jan. 31, 1979, and piled up 7.4 inches high. Snowplows don't exist in Southern Nevada and nearby cities, such as St. George, Utah, needed their plows.

Snowfalls that stick such as that from the 1979 storm arrive about every 20 years.

April snow is rare in Las Vegas, but the Sun reported on April 13, 1965, that it had snowed in some areas, including Boulder City.

Snow flurries fell in Las Vegas on April 2, 1997, and Mount Charleston, about 30 miles northwest of Las Vegas, was blanketed with more than 4 inches of the white stuff on that date.

The first measurable snowfall in the 1990s occurred Feb. 19, 1990 -- 1.4 inches at McCarran International Airport.

"It's going to be a severe wake-up call for a lot of people who don't expect snow in Las Vegas" if it snows this winter, McQueen said.

In looking more closely at what this winter will bring, McQueen said cold air is piling up in the Gulf of Alaska and Canada. "It's getting deeper and deeper," he said. "It's like a dam. When it gets full, the cold air streams down into the states."

Usually the river of cold air spills down the Continental Divide, but it can plunge into Nevada, bringing the threat of snow.

The cooler Pacific waters would mean less frequent storms in Southern Nevada, but that doesn't translate into a warm, sunny winter, McQueen said.

The storms will still strike Southern Nevada, but they will come less often. That's because weather is more complicated than the battle between hot and cold ocean waters.

The Jet Propulsion Laboratory in Pasadena, Calif., which is keeping track of the ocean's waters, has noted a slowing of the rapid cooling that began in the central tropical Pacific. La Nina has slightly decreased since August.

That flux leaves scientists uncertain about whether the cold pool will grow into a long-lasting La Nina. In turn, the uncertainty raises questions about predicting the weather for this winter.

During October and November, forecasters will continue to cast careful eyes on the Pacific Ocean, McQueen said.

"This winter will be completely different," McQueen said. "It could start out nice, then some storms will develop and maybe even a snowstorm."

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