Sierra Weather Instrument Corporation was founded in Nevada City, California in 1972.  An internet search indicates that the corporation still exists but that they have been suspended by the California Franchise Tax Board.  I interpret this to mean that they are no longer in business.  I don't know if they are connected with Sierra Instrument, which is a current manufacturer of flow meters.
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A 1975 catalog from Sierra Weather Instrument Corporation may be downloaded below (60 pages):