In February, the oysters in Tomales Bay are crisp, firm and delicious. But winter storms pose a challenge. “Before the rain comes, we have to harvest like mad,” said Heidi Gregory, manager of Tomales Bay Oyster Company. That’s because state law prohibits harvest after as little as half an inch of rain due to runoff from surrounding hills. Five tidal cycles are needed to clean the waters and reopen harvest. So repeated storms mean long…