Hi Dennis - it seems to me that you need to take a close look at each station when the alarm is 'lit'.

It could be instrument malfunction, like water got into the unit or some other reason.

I just looked at the Black Point sensor and its been showing the same basic pattern all month so I wouldn't count that one.
Mammoth has been up for 3 days and doesn't appear to be calibrated properly.
Carrizo Plain does look interesting...

Those are the only 3 sites showing alarm at this time.

Canie