Bring a large pot of water to a boil. Salt generously. Add the pasta and cook until al dente. Drain and rinse with cold water, then set aside.
In a large bowl, whisk together the mayonnaise, sour cream, lemon juice, old bay seasoning, salt, and pepper. Add the cooked pasta, the shrimp, the peas, the green onions, and the dill. Stir to combine.
Cover and refrigerate for at least 2 hours, or overnight.
