Alert: Operations Manager Web Console Unavailable
Management Pack Name: System Center Core Monitoring
Management Pack Version: 7.0.9538.0
Rule or Monitor: Monitor
Rule or Monitor Name: Web Console Watcher Monitor
Rule or Monitor Notes:
Issue: After an upgrade process for Operations Manager this issue may occur.
Resolution: Release Notes for Operations Manager in System Center 2012 SP1. After doing this, the monitor re-assesses health (15 minute default) and it closes the alert. This is also discussed on the last step in this blog post: How To prepare for the OpsMgr 2012 upgrade prerequisites: OpsMgr 2007 R2 CU Installation Order