If You Thought It Was Hot Wednesday…

The region's heat wave will intensify Thursday,  producing triple-digit highs over a vast area -- including downtown Los Angeles  -- while heightening the risk of wildfires in the Southland's mountains and  forests.

Prompted by high heat and humidity levels in the single-digit range, a  red flag warning signifying a high risk of wildfire was in effect in the  mountains and foothills of San Luis Obispo, Santa Barbara, Ventura and Los  Angeles counties, including the Santa Monica Mountain Recreational area.

The warning, covering both the Angeles and Los Padres national forests,  was scheduled to expire at 9 p.m. tomorrow.

In the Angeles National Forest, some 1,200 firefighters were battling  two blazes today -- the 1,700-acre Morris Fire, which broke out Tuesday, and  the 20-acre Station Fire, which began Wednesday. 

The National Weather Service attributed the region's rising heat to an  upper-level ridge of high pressure building over southern Arizona today and  expected to reach the Southland by Friday.

"...Hot and dry conditions will become more widespread than what was  experienced on Wednesday," according to an NWS advisory.

"Thursday through Saturday should bring the warmest temperatures, when  widespread triple digit temperatures are expected over the interior and valley  sections of the Southland."

A number of temperature records are likely to be broken, especially on  Friday, according to the weather service. It said hot and dry conditions will  persist through Saturday, but some cooling is expected by Sunday.

The NWS forecast highs today of 84 in Newport Beach; 85 in Avalon; 88 at  LAX; 90 on Mount Wilson; 100 in Long Beach and downtown L.A.; 101 in San  Gabriel and Anaheim; 103 in Burbank and Pasadena; 104 in Palmdale and  Lancaster; and 107 in Newhall and Woodland Hills.

Temperatures will come down somewhat on Sunday but the cooling trend  won't gain momentum until early next week.

"The long-duration heat event could pose health hazards for anyone  outdoors, especially for the elderly, small children and pets," the NWS said  in a statement, urging residents to drink plenty of water, wear loose-fitting  clothing and stay out of the sun as much as possible.

"Never leave children or pets in cars with the windows up or cracked  during the day, even for a very short time, as temperatures can quickly reach  lethal levels," the statement said.