“…(the weekend of July 4), where might you suggest?”
Typically pretty tough for trout this time of year. In a typical weather pattern for July I would say go fish the Yough near the dam release near the town of Confluence early in the morning or late in the evening. Any of the Delayed Harvest Artificial Lures Only (DHALO) waters will still have fish but again typically they are low and warm so your best shot is very early (5 – 8 AM). Because of the rain I believe there is potential for success throughout the day. If the water is discolored and high, because of so much rainfall try nymphs and/or streamers;like the white wooly bugger we used (small # 10 or 12). If it is low use a dry as the indicator and sunken ants. Deadly! You could extend your day (late morning and afternoon) by fishing for smallmouth bass on the Casselman river near the town of Confluence.
“How best to fish in low water conditions?”
No weight needed if it is low and you are fishing with nymphs. Saturate your fly in the water by pinching it below the surface. We call that process squeezing them wet. Rub your nymph in the mud prior to the first cast. They make products to simulate mud as well. A dry fly as the indicator with a nymph on the dropper is best. May be able to fish dry flies solely and coax them up.