Which end? in Montana

OK, I "have" to be in Calif the last week of May and likely the first in
June, but I could do a Mid-April to mid-May trip ( I tend to think in terms
of month long periods ) ... is runoff likely to muck that up? I'm under
the impression that the streams don't blow out, on average, until late May,
early June

Maybe the chances of more days of good weather are better the later I arrive
( and still have enough time for a good trip before runoff )