Although the U.S. Patent and Trademark Office has not yet made a formal announcement on the USPTO Systems Status and Availability webpage or the Office's Facebook and Twitter accounts, it appears that the Office has now restored access to the EFS-Web and Private Patent Application Information Retrieval (PAIR) system.  Patent Docs was able to access the EFS-Web as a registered eFiler -- although we were able to access a specific application via the EFS-Web, we did not test whether the system would actually accept an uploaded submission.  Patent Docs was also able to access a specific application using Private PAIR.  As of the time of this post on December 27, 2015, the Office did not appear to have restored Public PAIR.

UPDATED:  The USPTO Systems Status and Availability webpage was updated on December 27, 2015 to include the following information:

Systems are slowly being returned to service today with a goal of bringing all systems online and operational Monday morning, December 28.

Due to the extent of the damage to the systems that provide power to the USPTO's data center, we know that work will continue for the next several days.  Therefore, in order to keep systems protected and prevent damage, it is possible that some or all systems may need to be taken offline again.

We understand how critical these systems are for our customers, and our teams will continue to work around the clock to fully restore them as quickly as possible.  Based upon the results and the stability of our operations, we will keep deadline flexibility in mind and will closely monitor operations and evaluate whether any additional "holiday notices" similar to the one issued last week covering December 22 to 24 are needed.