There was a post (now removed) on Wunderground's blogs from Aaron that explains what the issue was
I'm going to make this brief, because we're not at 100% yet, but I
thought it was only fair to get some info out to the members.
I have a hard time relating yet ANOTHER outage this month to all of
you without a painful grimace, only because of the completely bizarre
circumstances surrounding all of these outages. I have yet one more
for you. Perhaps nobody expects the Spanish Inquisition, but I can
guarantee you that until today no one could expect the Fire Marshal.
Just before lunch today, the fire marshal showed up to examine the
fire safety systems in one of our data centers. Let me tell you right
now, the fire safety system works. It's awesome in fact. So awesome
that when the fire marshal failed to engage the test mode, and instead
went right to the "blow smoke at the detector" phase the entire data
center went out like we'd blown a fuse.
I can tell you right now, that the sound of a silent data center is
enough to make your heart drop into the pit of your stomach.
We're working on getting everything back up and running. Once again,
we're sorry for the down time, and the fire marshal will "test" our
fire system over my dead body.
-Aaron
Posted Jul 31, 2008, at 10:57 PM, Victor Engel on the CWOP mailing list.