By Susan Wood

Alarmists and the apathetic beware: one thing is clear when facing a tropical phenomenon like El Nino this winter — weather is not an exact science.

With a moderate El Nino predicted to bring average temperatures and slightly more precipitation, the National Oceanic and Atmospheric Administration and “2010 Old Farmer’s Almanac” have at least agreed in forecasting a season of extremes with snowfall and rain events quickly giving way to warm and dry California conditions.

The latter has led to a three-year drought in the state and Lake Tahoe falling below its natural rim for only the seventh time in the 109 years that records have been kept. Since Oct. 1 – when the water year starts — it dropped below the 6,222-foot mark twice. This week the lake level fell almost a quarter inch.

Consecutive drought years make the need for piers obsolete at Lake Tahoe. Photo/Kathryn Reed

Gov. Arnold Schwarzenegger has declared this another drought year.

Even with a rare post-Columbus Day storm that drenched the region and brought the lake level up by 2.6 inches over the 120,000 acres, the drought-like conditions returned and allowed evaporation of all that water that equals 8.7 billion gallons.

These extremes have climatologists, ski resorts and even basic weather watchers scratching their heads.

“There are certainly more variables, or I should say, extremes. But it’s been that way since the ‘70s,” said Gary Barbato, the National Weather Service hydrologist stationed in Reno.

The “Almanac” reports a winter of shoveling in December and power outages in January followed by an early quick thaw at the end of February into March.

Another water official is concerned about the frequency of the dry years and the intensity of the storms when they do show up.

“Tahoe can weather one year, but it’s harder with three, and we’ve had three in a row,” California Department of Water Resources hydrologist Morris Reuss said. “We’re hoping for a fairly decent water year.”

The average rise and fall of the lake level over the year may measure 3 feet. But when the loss totals 6 or even 9 feet over a three-year period, the pressure is applied to Mother Nature to make up the difference. And when she does, it’s sometimes too much, too fast. The runoff carries debris, sediment and silt into the watersheds. This movement into Lake Tahoe presents a whole other billion-dollar problem called lake clarity.

The Western Regional Climate Center has categorized the lake level drop as “not common, but not impossible,” said Reno climatologist Kelly Redmond, who just returned from a conference in Denver highlighting the properties of drought. The roundtable discussions included the possibilities of displaced populations in an “old-style” drought similar to, but not equal to, the Dust Bowl of the 1930s.

A report issued from NOAA this week noted October as having the sixth warmest global (land and ocean) surface temperature since 1880. The combined temperature measured 1.03 degrees Fahrenheit above the 20th century average of 57.1 F.

“With climate change, we expect a drying out of the Southwest and a wetter Northwest,” Redmond said.

Redmond, a resident expert on El Nino, indicated NOAA has remained rather “noncommittal on Lake Tahoe” facing any big winter.

“It should be slightly more wet, but not by much,” he added.

To put it into perspective, El Nino is a tropical weather phenomenon that originates off the shores of South America in which sea surface temperatures in the eastern Pacific Ocean show a warming trend around Christmas – hence the “Christ child” Spanish name for the weather phenomenon. According to NOAA, the current El Nino has prompted ocean temperatures to rise 11 degrees Fahrenheit. This rise creates weather disturbances and storms that can slam California.

El Nino’s above average precipitation focuses on weather in the Southwest section of California, with the Lake Tahoe Basin teetering on the cusp of a rainy South and a dry Pacific Northwest.

Indeed, certain El Ninos – usually considered strong ones as in 1982-83 and 1986-87 – have produced abundant snowpack in the Sierra Nevada.

Whether it measures up to the anticipation from the scores of Tahoe die-hards who showed up in full force over the past week at Pray for Snow parties remains to be seen. “El Nino” flew off the tongues of skiers and boarders eagerly waiting winter as much as the beer, snacks and snow calls.

Either way, today’s forecast is a good start.

A winter storm warning was issued by the National Weather Service starting at 1pm and ending at 10pm Friday. Moderate to heavy snowfall measuring 8 to 16 inches along the Sierra Nevada crest above 7,000 feet and 3 to 8 inches is forecast at lake level. Near zero visibility is expected due to strong wind, which could make for hazardous driving conditions.

The calendar says winter starts Dec. 21, but Tahoe says it’s here now.