Topography Makes L.A. a Microclimate Brewery

By ERIC SLATER

Feb. 27, 1998 12 AM PT

TIMES STAFF WRITER

Would-be visitors to Los Angeles have followed the recent blusters of El Nino with great distress. They know that 13 1/2 inches of rain since Feb. 1 does not bode well for a sunny winter vacation on the beaches of Southern Cal.

If they only knew the whole story.

The measurements that most of the country and the world see when checking out the weather in Los Angeles come from a National Weather Service station at the Civic Center downtown. But Los Angeles County is a grab bag of wildly differing microclimates, many of which endure considerably more wind, rain and other meteorological maladies than the Civic Center.

Northridge received nearly 3 more inches than the Civic Center’s 13 1/2 so far this month, according to the National Weather Service. San Gabriel got nearly 5 more inches. Chatsworth soaked up a total of 20 inches.

And the green campus of UCLA grew greener with 20 1/2 inches, just a few miles west of City Hall.

North of Los Angeles, Ojai was swamped by nearly 23 inches of rain. Palmdale residents, meanwhile, have enjoyed a relatively galoshes-free month, with just 6 1/2 inches falling in the Antelope Valley suburb.

“This is one of the most diverse places in the world, with a tremendous difference between the coastal plain and the mountains . . . and the desert,” said National Weather Service Meteorologist Gary Ryan. “There’s a bigger difference in elevation between the Los Angeles Civic Center and its surrounding mountains than Denver and its surrounding mountains.

“Our mountains,” Ryan declared, “don’t get the credit they deserve.”

Indeed. It was not Denver, or Eureka, or Astoria, Ore., or Bainbridge Island, Wash., that recorded the heaviest-ever deluge west of the Rocky Mountains. It was a place meteorologists speak of with reverence: Hoegees Camp, just southeast of Mt. Wilson.

On Jan. 22, 1943, the mournful-looking clouds that had been piling up against the San Gabriel Mountains literally spilled their guts, emptying themselves of 26.12 inches of rain by the stroke of midnight.

Mostly, meteorologists say, rainfall is a matter of elevation, wind patterns and relief--the difference between elevations in a given area. And when the mountain ranges that circle and divide Los Angeles are factored in, as well the winds off the Pacific Ocean and other largely understood phenomena, L.A. weather makes sense.

Mostly.

“Most of the time, being a weather forecaster in Los Angeles is a pretty boring job,” said Ryan. “But it does have its moments. I think we proved that this February.”

The rule of thumb when it comes to rainfall is: The higher you are, the more rain falls on you.

As air rises, it cools, dropping between 2 degrees and 5 degrees per 1,000 feet of altitude depending on the amount of water vapor in the air, meteorologists say. And cooler air can’t hold as much water vapor as warmer air--which is why, between 1961 and 1990, Mt. Wilson, at 5,730 feet above sea level, received an average of 37 1/2 inches of rainfall each year compared with 15 1/2 inches at Van Nuys, which is nearly 5,000 feet lower, or the Civic Center, which got 14 1/2 inches at 260 feet.

It is more complicated than that, however.

Of the 685 recorded rainfalls of 10 inches or more in a day, dating to 1871, virtually all of the downpours took place on the windward side of ridges that face into an unobstructed airflow from the Pacific, said Jim Goodridge, formerly the state’s official climatologist.

“That’s where the wind is cooled quickly, and its ability to hold that moisture just disappears,” said Goodridge, who spouts century-old meteorological data as though the storms occurred yesterday.

The majority of the 10-inch downpours have occurred in the mountain ranges stretching from San Bernardino, through Los Angeles, to Santa Barbara.

With the mountains squeezing the moisture out of the clouds, there is less rainfall for valleys such as the San Fernando, which is almost entirely surrounded by mountains.

In the Antelope Valley, the effect is so noticeable that the cities of Lancaster and Palmdale are said to rest in the “rain shadow” of surrounding ranges, and receive only a half-dozen or so inches of rainfall a year.

That is less than half the rain that falls on most sites across the floor of the San Fernando Valley, even though Palmdale’s elevation of 2,659 feet is more than 1,000 feet higher than most San Fernando Valley sites.

Ah, but comparing sites even in the same valley can be dangerous. Even in the same suburb.

Even on the same street.

Irv Sherman has been keeping records on Woodland Hills weather for 26 years and has seen the temperature dip from just above freezing to just below as he drives downhill from his home on Killion Street. He’s the official National Weather Service “spotter” for Woodland Hills, and has measured 19.31 inches of rain this month.

William Russell is a professor of meteorology and geography at nearby Pierce College, which is located in Woodland Hills but, due to a decades-old ZIP-Code glitch, provides official weather data for Canoga Park.

Russell has measured 18.07 inches of rain since Feb. 1.

The official National Weather Service Web page, however, lists the February total for Woodland Hills as an extra-whopping 24.43 inches, as measured by an automated gauge hardly more than a mile from Sherman or Russell.

Sherman doubts the figure. Russell doubts it too. And the National Weather Service’s Ryan says, without a doubt, it’s just plain wrong.

It certainly gives those would-be visitors a little something to think about though.

(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)

February Rain

Inches of rain for February to date.

Ojai: 22.65

Santa Barbara: 21.74

UCLA: 20.50

Chatsworth: 20.11

Ventura: 18.91

Oxnard: 17.80

Simi Valley: 17.20