Potomac is the newer service center, which I guess is why it's harder to find the processing times. The USCIS website lists the I-130 processing time at Potomac at 5 months. Mine was recently approved there after 4 months. This seems somewhat faster than at least the Nebraska service center, so if you're feeling impatient after just 3 months, you're in for a long journey here!
You can find a list of petitions being processed here:
Just choose Potomac under service center. You'll see the recent approvals, which include cases from July through September. There are still cases from June who have not had their petitions approved. There have been zero cases from October approved yet from Potomac on this site. Be patient... you'll get there!
Aseda reacted to Mme D in Processing times for Potomac