Starting at dusk tonight, a band of lights around the top of the One Rincon Tower in San Francisco will turn the building into a weather beacon, glowing amber, blue, red or green to forecast the weather, a bit like a 64-story mood ring.

Lighting up the top of a building to predict the weather has been a tradition most notably in Boston, where the John Hancock Building was opened in 1949 and featured blinking red and blue lights to forecast the weather.

Weather beacons are also used on tall buildings or towers in Syracuse, N.Y; Minneapolis; Dubuque and Des Moines, Iowa; Bismarck, N.D.; Toronto; and in two tall buildings in Brisbane and Adelaide, Australia.

The beacon atop One Rincon Hill will be the first in the Bay Area, although there is a weather beacon atop a television tower in Sacramento.

The lights will cast an amber glow around the top of the One Rincon Tower if the weather is forecast to stay about the same. The lights will glow blue if the forecast calls for a five degree drop in the average temperature, red if the temperature is expected to go up more than five degrees. If there is a 50 percent chance of rain in the forecast, the beacon will be green.

One Rincon's developers have composed doggerel to go with the lights:

Glowing red, warmer weather ahead

Shining blue, colder weather in view

Going green, rain foreseen

Amber light, no change in sight.

There seems to be no light to indicate fog, a summertime weather pattern that often envelops One Rincon. The building, which rises 694 feet above sea level, stands by itself atop San Francisco's Rincon Hill.

The beacon will go on at dusk every day and will remain on all night. One Rincon building engineer Ben Irving will review the National Weather Service forecast for San Francisco and determine the color of the lights every day.

The lights -25 LED floodlights - burn very little energy, according to David Kriozere, one of the developers of the building and the son of principal developer Michael Kriozere. The lights are designed to last about 40,000 hours before they have to be replaced.

The light beacon is mounted on the so called "crown" of the building, a structure that conceals a 50,000-gallon water tank designed to control the sway of the tower in a high wind.

The glass crown, which is illuminated to form the beacon, rings the south, east and north sides of the building-this means the weather beacon is most visible from the East Bay or the Bay Bridge. A metal shield on the building blocks part of the weather display on the western side of the building.

The country's first weather beacon featuring colored lights was installed on the Empire State Building in New York City in 1941, but it was discontinued after the attack on Pearl Harbor on Dec. 7 that year.

According to the One Rincon developers, weather beacons atop buildings or towers are usually used by TV stations or banks as advertising tools. The beacon atop One Rincon is the first on a residential building, according to Kriozere.

"We hope this weather beacon will only add to the beauty of San Francisco's skyline and One Rincon Hill's place in it," said Kriozere said. "It's our gift to San Francisco and the Bay Area during the holiday season."