Planet Ragnar is a gas giant and neighbor of the Twelve Colonies of Man. The planet is noted for its violent electrical storms and calm spot, which is the opposite of Jupiter's calm surface and viloent storm spot.
Ragnar is the location of the Ragnar Anchorage, a munitions station where Colonial ships refuel and restock. The storms interfere with scanners(which hides the Anchorage from enemy scans) and makes it difficult to make FTL jumps. In order to make a jump, a ship must pass over the EM threshold in the main bulk of the upper atmosphere.
Another effect of the storms is the radiation given off by them, which had been discovered to damage Cylon technology and the Cylons themselves. This promts them to leave the planet alone.