Firefighters will not get much of a break from the weather over the next day or so, as strong dry winds are expected through Thursday morning. The National Weather Service posted a red-flag warning for a 20,000-square-mile area of Northern California into the morning. “Any fire will spread rapidly,” weather service officials said. The warning covers the areas affected by the current fires raging in the North Bay and Mendocino County, but also extends from the upper end of the Sacramento Valley through the coastal hills as far south as the Santa Cruz Mountains and Diablo Range. The entire area is nearly twice the size of Massachusetts and has a population of 4.3 million people.