The Lochsa will likely be low, barring a rain event. I consider low below 4' (not the gauge height from the internet gauge) or 8000'. It is still a hoot, lots of rapids and plenty of interesting things to go into, but it's true nature starts to show at 4. Med is 4-6' (8000-14,000) when it is getting big and fun and pushy. High is 6+, 14k and up. Last weekend it hit 20k, wish I had been there. The most fun on the Lochsa is doing the upper section, meatier and more technical, but below 4' the water slows so much doing the entire run in one day makes for a long day. 4' and below and the upper loses it's claim over the lower section. You'd probably enjoy Fish cr too, a tributary that you can drive 1 mi up and hike further. If you like the NFP you also should check out the SF clearwater, golden canyon section. Even the mickey mouse section is great, more technical than the lochsa, lower volume ledges and holes.
Living in Montana, boating in Idaho