I'm from the area Steve and the Monocacy is a fantastic warm water fishery. One down side is the indian meaning on the river, which translates to "muddy river". From it's headwaters in PA, it flows through many miles of farm land and dirties very quickly. If it is clear, then it's great to fish. Be warned! If the river is slightly off color, it can be extremely scary. I have personally stepped into a hole over my head in off-color conditions. Going from waist high to not touching the bottom is never cool. And there are a ton of holes like that.
I personally prefer it's lower reaches a few miles up river from the mouth at Dickerson. If you go be sure to carry silver poppers and olive streamers / buggers.
You can't judge clarity from the USGS stream gauges either. If there is a good storm the night before upstream, there's a very good chance that the river will be off-color and low.
If you decide to go and it's blown out, then you have the mighty Mac as a back up. You will only be a half hour away from some of the best smallie fishing on the Mac. You'll be about an hour away from the Shenandoah River. I recommend fishing above the dam and below in the Millville area. It is heavily patrolled, but has excellent smallie fishing with nice runs and long slate pools.
Good Luck and BE SAFE!