I live in the Methow and Big Twin is the lake that would usually fill your bill. It did apparently have some winterkill, this year, but I have fished only one evening, so far. Got a few in the mid-teens. When winterkill is not an issue, it's not uncommon to find 20"+. Chronomids, for now, with some decent hatches in the evenings.

If you have some extra time and gas, there are some lakes up in the Sinlahekin (North of the Methow; west of the Okanogan) that are worth checking in to. Blue, a few miles N of Conconully, is one.