Bring a large pot of lightly salted water to a boil. Cook elbow macaroni in the boiling water, stirring occasionally, until tender yet firm to the bite, about 8 minutes. Drain, rinse, and transfer to a bowl.
Combine mayonnaise, sour cream, vinegar, sugar, dry mustard, salt, and pepper for dressing in a small bowl; mix well. Pour over pasta.
Add dressing, green onions, celery, bell pepper, peas, and parsley to the pasta. Mix until well combined.
Chill in the refrigerator for 2 to 3 hours before serving.