The April-July runoff forecast into Lake Powell, on the Arizona-Utah border, is just 52 percent of the long term mean, according to new numbers out today from the Colorado Basin River Forecast Center.

That is roughly 1.3 million acre feet less water flowing into Lake Powell than the forecast of just a month ago, the result of a hot, dry March. That means at the end of said runoff period, Powell will be roughly 13 feet lower than it would have been otherwise, according to my half-assed amateur calculation (danger, danger, journalist doing math! – the pros at the Bureau of Reclamation will give us a more reliable number next week).

It’s important to remember what this means. Unlike in California, where farmers directly downstream from reservoirs get shorted when inflow is lousy, Powell is a giant bathtub in a super-plumbed system. While farmers using headwaters streams and rivers to irrigate could see shortages as a result of the lousy snowpack, the real impact for the Colorado River Basin system as a whole is more buffered. But in the long run, it increases the chances of seeing a formal shortage declaration in coming years, which would reduce allocations to Arizona and Nevada.