WINTER WEATHER : VALLEY AWAITS COLDER WEATHER AND PRECIPITATION

Sunny California isn’t always so sunny. In the Valley region, roads become blocked with snow or flooded, some even by slight rainfall. Falling temperatures prompt officials to convert the National Guard Armory in Encino into a shelter for the homeless every winter, often before similar shelters are opened in other, warmer, parts of the city.

The Golden State Freeway, the state’s main north-south artery, is shut down an average of three to 10 times a year in the Gorman area due to snow, forcing some to take refuge in motels and restaurants in Castaic. And as any desert dweller will tell you, the high temperatures that blister the Antelope Valley in summer give way to winters that leave snowy blankets on the Joshua trees.

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VALLEY WEATHER

So why does it get so cold in the San Fernando and nearby valleys? One simple answer: cold air tends to pool in valleys. Distance from the ocean also keeps temperatures low, especially in desert areas. Elevation plays a role as well. Van Nuys is 700 feet above sea level, compared to 260 for the Los Angeles Civic Center. Newhall rests at 1,210 feet. Lancaster, which is colder still, is at 2,340 feet.

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THE FORECAST

WeatherData Inc., which provides forecast information for The Times, predicts a colder and wetter winter this year. Valley weather watchers take note: The 1992-1993 rain season, which runs from July 1 to June 30, dumped more than 24 inches of rain on Woodland Hills.

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DETECTING UNSAFE ROADS

Caltrans installed the “Scan-cast” computer system--short for surface condition analyzer and forecast-- along a 30-mile stretch of the Golden State Freeway in 1990. The system, similar to one used on airport runways, helps Caltrans pinpoint weather problems on the highway. Additional equipment is being added on the Golden State soon will be installed on the Antelope Valley Freeway.

Here’s how it works:

* Eleven sensors are embedded in the pavement and four atmospheric sensors positioned along the highway between Castaic Lake and Fort Tejon.

* Sensors measure precipitation, temperature, wind speed and even chemical factors, such as oil or salt, on the roadway.

* Sensors transmit up-to-minute data to command center in Lebec, near Kern County line.

* Caltrans dispatches snow plows and trucks to clear snow or pour sand and salt for ice.

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THE STORM OF 1989

The most recent major snowstorm hit the Valley area struck Feb. 8, 1989, leaving as much as five inches piled up in Westlake Village, Porter Ranch, Calabasas, Tarzana and Granada Hills. The blustery Arctic storm deposited six inches of snow in the Santa Clarita Valley, essentially sealing off the community, closing roads and shutting down schools.

PRECIPITATION Average precipitation in inches per month*

NOV. DEC. JAN. FEB. Burbank 1.75 2.27 3.1 3.4 Lancaster 0.59 1.1 1.37 1.55 Newhall 2.24 2.44 3.73 3.55 Van Nuys 1.85 1.82 3.48 3.36 Woodland Hills 2.06 2.15 3.51 3.29

*Averages figured from years 1949 to 1993 *

SNOWFALL While most of these locations average only a trace of snow, here are some extremes.

Monthly snowfall Month, Year Burbank 4.7 in. January, 1949 Lancaster 23.9in January, 1979 Newhall 3.0 in January, 1962 Van Nuys 7.5 in January, 1949 Woodland Hills 0.5 in. February, 1989

TEMPERATURES Average* highs and lows, in degrees.

NOV. DEC. JAN. FEB. Burbank 73/46 68/42 67/41 69/43 Lancaster 66/35 58/29 57/30 61/35 Woodland Hills 75/43 69/39 68/39 70/41

*Average figured from years 1949 to 1993 Temperatures not available for Newhall and Van Nuys Sources: Weather Data Inc. and Caltrans; Researched by STEPHANIE STSSEL / Los Angeles Times