 The dry line may occur anywhere on earth in regions intermediate between desert areas and warm seas . The southern plains west of the Mississippi River in the United States are a particularly favored location . The dry line normally moves eastward during the day and westward at night . A dry line is depicted on National Weather Service ( NWS ) surface analyses as an orange line with scallops facing into the moist sector . Dry lines are one of the few surface fronts where the pips indicated do not necessarily reflect the direction of motion . 
