 These features are often depicted in the warm season across the United States on surface analyses and lie within surface troughs . If outflow boundaries or squall lines form over arid regions , a haboob may result . Squall lines are depicted on NWS surface analyses as an alternating pattern of two red dots and a dash labelled SQLN or SQUALL LINE , while outflow boundaries are depicted as troughs with a label of OUTFLOW BOUNDARY . 
