No Relief in Sight

Updated 8:16 AM PST, Wed, Jul 22, 2009

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Johnny and Debbie Lanzarotti

Get used to the triple-digit temperatures.

The Southland once again will bake under sizzling temperatures Wednesday, with the region's heat wave showing no clear sign of dissipating. The National Weather Service forecast highs in the low 100s in the San Fernando, Santa Clarita, San Gabriel and Pomona valleys and the mountains of Los Angeles County, other than the Santa Monica range.

Because the humidity level -- now at the 20-30 percent level -- is expected to make the heat particularly uncomfortable in the mountains, an excessive heat warning will be in effect for mountain areas until at least 8 p.m.

"The combination of temperature and humidity will create dangerously hot conditions, with heat index values climbing to 100 degrees or more" in mountain regions, according to an NWS advisory.

The heat index is a measure of discomfort based on humidity and heat, which could peak at 105 in mountain areas Wednesday, forecasters said.

The Antelope Valley is expected to experience highs of 108. On Tuesday, the mercury climbed to 107 in Lancaster, setting a record for a July 21, besting the one set in 2006, when the temperature in the city reached 106.

How much longer the heat wave will last was not certain Wednesday morning as meteorologists struggled to forecast the departure of a strong upper-level high-pressure system that has been parked over the West for several days.

One computer model indicates that it will push eastward starting Monday or Tuesday, but another one shows the system staying put, said meteorologist Jamie Meyer in a telephone interview from the NWS office in Oxnard.

In any event, we will not see "a whole lot of change anytime soon," she said.

The NWS forecast highs today of 74 in Avalon; 75 at Newport Beach; 76 at LAX; 85 in Long Beach; 88 in Anaheim; 89 in downtown L.A.; 90 on Mount Wilson; 93 in San Gabriel; 94 in Burbank; 96 in Pasadena; 102 in Woodland Hills; 104 in Newhall; and 106 in Palmdale and Lancaster.