UNSC Weather Station Z/41
From Halopedia, the Halo wiki
Template:Ratings Weather Station z/41 is a United Nations Space Command facility in the Arctic on Earth [1]. It is the setting for the Halo 3: Legendary Pack map, Blackout.
In the Weekly Update that unveiled Blackout, some of the Bungie guys joked that it was a "stupid and arbitrary name" with "no significance", and left it to the fans to find their own meaning in the name z/41.