Los Angeles, Shawwal 21, 1436, August 06, 2015, SPA -- California fire authorities were bracing for lightning strikes from scattered thunderstorms forecast for Thursday, while dry, powerful winds were raising the threat posed by a major blaze in Washington state, according to dpa. The California Department of Forestry and Fire Protection (Cal Fire) was on a high alert and warned of the risk of new lightning-sparked fires in the state's drought-parched northern inland region. The largest single existing blaze was affecting at least three counties north-west of state capital Sacramento, Cal Fire said. The so-called Rocky Fire has already scorched more than 27,000 hectares, destroyed 39 homes and 52 outbuildings and forced mandatory and voluntary evacuations of 13,000 people, the state said Wednesday. With nearly 3,500 firefighters deployed, the blaze was described as 20 per cent contained, after crossing a state highway on Monday where Cal Fire had hoped to halt the conflagration. Cooler, more humid weather slowed fire activity on Tuesday, allowing crews to build containment lines ahead of the flames. "The cooler temperatures really aided firefighters in their efforts," Cal Fire spokesman Daniel Berlant said. Hotter conditions were expected later Wednesday, potentially complicating work to control the fire, he said. Dozens of other large fires, some covering thousands of hectares each, were blazing in the state, especially northern California. One in coastal Humboldt County "is actually made up of over 70 smaller fires making up a little bit over 3,000 acres [1,200 hectares]" due to lightning strikes, Berlant said. Statewide, more than 10,000 firefighters are on the front lines organized into 227 crews, with 770 fire engines, 153 bulldozers, 57 helicopters and dozens of large air tankers, he said. Other states are providing wildfire crews to give California firefighters brief respites. Thunderstorms in Thursday's forecast present new dangers, Berlant said. "While they might cool temperatures just a bit, they're going to have the possibility of more dry lightning, sparking more of these wildfires," he said. "So crews still on high alert." With an ongoing drought in much of California, the pace of fires this year is already more than 50 per cent above the average through seven months, Cal Fire said. Farther north up the Pacific Coast in Washington state, a fire along the Columbia River in the state's arid inland region broke out Tuesday and by Wednesday morning grew to 4,000 hectares, the state's Emergency Management Division said. The blaze threatened 350 homes. The fire was near tiny Roosevelt, Washington, on the north bank of the Columbia River, which forms the state line to neighbouring Oregon. All 200 residents were evacuated from the village, about 210 kilometres east of Portland, Oregon. The National Weather Service issued a red-flag warning for critical fire weather conditions, forecasting a "combination of gusty winds and low relative humidity values" for the fire-stricken lower Columbia basin of Washington and Oregon, as well as the Yakima Valley and the foothills of the Blue Mountains. Sustained winds were expected as high as 35 kilometres per hour with gusts approaching 50 kilometres per hour, amid humidity below 20 per cent. "Any fires that develop will likely spread rapidly. Outdoor burning is not recommended," the weather service said in a statement from its office in Pendleton, Oregon. The Federal Emergency Management Agency issued a declaration Wednesday making federal fire management assistance available for the Roosevelt blaze. --SPA 03:32 LOCAL TIME 00:32 GMT www.spa.gov.sa/w