March Mildness

The thermometer in downtown Los Angeles soared to 92 degrees Monday--unseasonably hot but still four degrees short of the record--as a winter that began seasonably cool and a lot wetter than usual is ending up unseasonably warm and dry.

Forecasters say that while temperatures will cool off a little over the next few days, there’s still no rain in sight.

Todd Morris, a meteorologist with the National Weather Service in Oxnard, said it’s all part of the typically atypical weather of Southern California.

Back in December, when winter officially began, a vast trough of low pressure lurked persistently off the West Coast, funneling storms south from the Gulf of Alaska and directing them into the Los Angeles area. Morris said the trough also sucked up subtropical air from the eastern Pacific that added to the moisture of the storm systems.

The result was plentiful rain--4.09 inches of it in Los Angeles, about twice the normal amount for December--while temperatures averaged out to normal.

In January, he said, the trough continued to hang off the coast. The downtown rainfall total for that month was 5.58 inches--again about twice as much as usual--and temperatures again averaged near normal.

“Then things changed,” Morris said. “The low-pressure trough was replaced by a high-pressure ridge that anchored offshore. That kept the storm systems well to the north, and there went the rainfall.”

In February, when normal rainfall averages out to 3.07 inches, a scant 0.08 of an inch fell in downtown Los Angeles.

“And now, in March, we’ve changed even further,” Morris said.

The ridge has moved onshore to form a giant dome of high-altitude high pressure directly over the coast, he said. This stationary dome, he said, is continuing to block out any storms.

Morris said that beneath the dome, low-level air from another high-pressure system near the Great Basin is circulating into Southern California, creating gusty offshore winds that are heated and dried out by compression as they sweep down mountain canyons toward the sea.

The result: unusually high temperatures throughout the Los Angeles Basin on Monday. The downtown reading of 92 was 23 degrees above the normal high for the date. Other top readings Monday included 98 in Monrovia--the hottest spot in the nation--94 in Montebello, 92 in Woodland Hills, 91 in Northridge and 90 in Redondo Beach.

Morris said his computer models keep promising the return of an offshore, low-pressure trough that could mean more rain, but thus far, that trough has failed to materialize.

“It’ll get a little cooler, with highs in the upper 70s and low 80s on Tuesday, and in the 70s on Wednesday--but that’s still warmer than normal,” Morris said. “And there won’t be any rain.”