More than a million acre feet of water disappeared from Lake Powell in the latest U.S. Bureau of Reclamation operational forecast for the 2015 water year, translating to a 13 foot drop in the big Colorado River reservoir’s projected end-of-September elevation in this month’s forecast compared to just a month ago.
The change in this month’s USBR “24-Month Study” (pdf) is the latest fallout from a dismal March, with hot temperatures and little snow across the Colorado River Basin.
For now, the forecast will have little impact downstream at Lake Mead, the reservoir that supplies Arizona, Nevada, and California. Mead is at historically low levels (where by “historically” I mean “lowest since it was filled”) and is teetering on the brink of a shortage declaration, so the numbers here matter, but the latest forecast suggests the odds remain against a 2016 formal shortage declaration (gory details of what “shortage” means here). But the forecast contains a caveat that, if the crappy weather continues, released from upstream Powell to downstream Mead could be throttled back later this year, which would Mead closer to the shortage line by the end of the year.