Some Things in the Air : Weather: Santa Ana winds hit 40 m.p.h, knocking out power, spreading embers and aggravating allergies. Fire danger high.

Gusty Santa Ana winds reaching 40 m.p.h. interrupted electrical service in several cities Thursday, spread a tree fire to a nearby apartment building in Orange and generally wreaked havoc on allergies, authorities said.

Winds generated by a moderate Santa Ana condition are expected to continue gusting today but will taper off by the afternoon, according to meteorologist James McCutcheon of WeatherData Inc., which provides forecasts for The Times.

Wind-whipped sparks from a tree fire in Orange caused an estimated $16,500 in damage to the roofs of three apartments in the 1900 block of East Coral Avenue in Orange, authorities said. A maintenance crew was welding wrought iron about 2 p.m. when the tree caught fire.

The sparks were blown onto nearby roofs, according to Battalion Chief Doug Mochizuki of the Orange Fire Department. More than 30 firefighters from Orange and Anaheim extinguished the blaze without injury, and residents of the apartments were allowed to return later in the day.

The Santa Ana conditions prompted firefighters around the county to beef up patrols, said Emmy Day, a spokeswoman with the Orange County Fire Authority.

“With these winds, a fire could easily be carried from a single roof to a whole neighborhood,” Day said.

Prolonged Santa Ana conditions could accelerate the drying out of lush hillside brush and usher in an early fire season, which usually starts in May, Day said.

“The potential is there for an incredibly dangerous fire season because of these winds,” she said. “There’s more undergrowth now than the winter before the Laguna Beach fires (in 1993). There’s more to burn out there than I’ve seen in a long time.”

The high winds also dropped a tree branch into a Tustin substation of Southern California Edison shortly after 9 a.m., knocking out power to about 11,000 homes for 38 minutes, said Chriss Brown, a power company spokesman.

Winds also caused sporadic outages among about 3,000 homes in parts of Santa Ana and Costa Mesa, but all power was restored within an hour, Brown said.

At John Wayne Airport in Costa Mesa, tower officials reversed the normal directions for outgoing airplanes as is standard during Santa Ana winds, according to airport spokeswoman Pat Ware. Aircraft, which take off heading into the wind, departed to the north instead of the south, she said.

Meanwhile, allergy sufferers took it on the chin--as well as nose, eyes and sinuses. The dry, hot winds blow in all kinds of tiny irritants--mostly weed and grass pollen, mold spores and dust--which stir up allergies and aggravate eye, skin and respiratory conditions, allergists said.

“Allergies are flaring up today,” said Dr. Donald Levy of Orange, who is an allergist and immunologist. “We’ve been much busier over the past days because of the winds.”

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Into the Wind Normal southbound takeoffs at John Wayne Airport are switched to the north during strong Santa Ana winds. Departing planes must take off into the wind to increase the lift effect caused by airflow over the wings. How lift works: *

1. Plane takes off into wind. 2. Shape of wing accelerates air flowing over it, lowering pressure above wing 3. Air flowing under wing is unchanged 4. Relative difference in pressure causes lift *

Runway Reverse John Wayne departure direction is reversed when winds blow at 5 knots or more. A knot is a unit of speed equal to 1.15 m.p.h. *

Northern Exposure * About 10% of takeoffs are to the north. * Northerly departures are easier because no noise abatement maneuvers are needed. * Planes climb to 4,000 feet before turning. Sources: John Wayne Airport, World Book Encyclopedia; Researched by CAROLINE LEMKE / Los Angeles Times