FRESNO — A cold snap that has California farmers struggling to protect a $1.5 billion citrus crop has slowly started to ease, though frigid temperatures were still the norm Tuesday morning throughout the state and across other parts of the West. For a fifth night, temperatures in San Joaquin Valley, California’s agricultural heart, dipped as low as 21 degrees. “It was still a critical night” even though the temperatures were a degree or two warmer than previously, said Bob Blakely, director of industry relations for Exeter-based California Citrus Mutual, an association representing 2,200 growers who have roughly 65 percent of …