Any historical prediction of flows on the Virgin won't work. The North Fork is almost entirely snowmelt and is dependent on daily temperature, albedo, and wind conditions. The weather in southwest Utah has been cool and wet through this spring. Snowmelt is starting, should increase the flow through this weekend, but snow is predicted for the high country Tues-Thurs next week. That will turn the flow off like a faucet. Zion does not issue permits for boating when flows are less than 140 cfs, part of a negotiation that allowed private vehicle shuttle access within the canyon, contained in the Superintendent's compendium (2002) of the Master mangaement plan.That said, there is (probably) boatable water at the put-in. Have not had any eyes on it yet.
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