In a medium bowl, combine the buttermilk, sour cream, mayonnaise, parsley, dill, chives, lemon juice, onion powder, salt, garlic powder, and black pepper. Whisk until smooth.
Season with more salt, pepper, and lemon juice to taste.
Store in the refrigerator for up to 1 week.
Notes
The dressing will thicken again after it has chilled. Simply shake it up and let it sit at room temperature for about 15 minutes to warm up a touch. Or thin it out by adding a splash of buttermilk or water.