According to Slack support at 1:20pm PDT, "We are currently seeing a connectivity problem where some teams are unable to load Slack. We are very sorry for this disruption. We're working hard to solve it as quickly as we can. We will update this page with more information as it becomes available."
As of 1:38pm PDT: This issue is specifically affecting IBM, so this outage is considered resolved for all other users.
Please let us know if you have any questions by calling us at 650-454-8850.