A story arc is an extended or continuing storyline in episodic storytelling media. Throughout the show's 10 year run, there have been only 3 story arcs ever made to date.
The first one involved the debut of Periwinkle. He moves to the neighborhood in Blue's Big Mystery, talks about how moving has effected him in Periwinkle Misses His Friend, and later on in the next season, his friend that he talked about came to visit the neighborhood.
The second one involved the birth of Cinnamon. It is the longest story arc at 5 continuous episodes. Even though it was a major factor in each episode, it was however not the main focus of each particular episode. "What's New Blue" involved the making of a newspaper, which lead to the announcement of his coming, "Blue's New Place" dealt with Blue having set up a new place by the bookshelf in the bedroom, as she wanted a quiet place to read. The arc in this episode involved Paprika moving from her crib to her new bedroom so the crib and baby toys could be used by the new baby. "Mr. Salt and Mrs. Pepper Day", involved the whole house throwing an appreciation day for the two, since they had done so much to keep the house together. The baby is only mentioned once, but throughout the episode, Mrs. Pepper is shown to be very pregnant with Cinnamon. "The Baby's Here" is when the story arch gets full attention, as it is the episode that Cinnamon is born. Mr. Salt and Mrs. Pepper have to leave for the hospital right as the Viewer arrives, and later on in the middle of the episode, the baby is born. By the end of the episode, Cinnamon is brought home and ready to start life in the Blue's Clues House. "Making Changes" continued right from the last episode, focusing on Cinnamon, but this time, instead of waiting for the baby to arrive, this one showcased what it can be like with a newborn in the house. Loud noises and certain activities needed to be altered when it came to helping Cinnamon becoming comfterable in the new house. This episode ends this the arc, and adds Cinnamon as a reoccurring character.
The third story arc can be summarized with the TV special, Joe's Scrapbook which was skipped in the international versions not involving Steve or Joe as the host.