A 'vowel outage' is exactly what you would think; and Google's Gmail had such an outage for a while today. The problem has been solved, but for a while it was frustrating for the users afflicted. The letter 'Y', which is only a vowel sometimes, was not effected; and no that is not a joke.
"Over the last hour we've received numerous reports of this issue via our help forums, from colleagues at Google, and via email you’ve sent us. Some of you have already found creative workarounds for communicating without vowels, like Aaron, who sent us this:
Having 80.8% of the alphabet available is significantly below the 99.9% full letter uptime reliability we strive for. Since identifying the root case of this issue, we’ve started bringing vowels back to Gmail, so you should see them back in your account within the next few hours if you don’t already."