The Bureau of Reclamation publishes a 24-Month Study every month, projecting the elevations of Lakes Powell and Mead two years out. Read one at a time they are routine. Read as a series, tracking what each successive edition said about one fixed future date, they show a forecast moving in a way no individual study reports.
The date that matters is 1 January 2027, because under the 2007 Interim Guidelines Lake Mead’s projected elevation on that day is what sets Lower Basin shortage conditions for the year that follows. Across the twelve editions from August 2025 to July 2026, that projection ran 1,049.44 feet, then 1,049.93, 1,053.51, 1,054.62, 1,057.62, 1,060.13, 1,058.35, 1,056.87, 1,056.36 — and then, in the May 2026 edition, 1,037.03. The fall of 19.33 feet in a single month compares with a next-largest single-edition move of 3.58 feet in either direction. It has stayed there since: 1,036.83 in June, 1,037.31 in July.
Reclamation announced the reason itself, in the window between the two studies. On 17 April the Interior Department said it would reduce the annual release from Glen Canyon Dam to 1.48 million acre-feet to protect elevations at Lake Powell, and stated in the same announcement that the measure would accelerate the downstream decline of Lake Mead. The May study is the first edition to carry that decision, and the accompanying movement in stored water — roughly 1,376 thousand acre-feet across the two reservoirs — accounts for the elevation change at Mead’s surface area, with the residual sitting in evaporation and a Flaming Gorge release.
The 1,050-foot line is the one worth watching in that series, and it is also the one that is about to stop meaning anything. Under the 2007 guidelines, a projection below 1,050 feet moved the Lower Basin from a first-tier shortage into a deeper one. The projection has now sat below that line in five of the twelve editions, including the first two — so the May drop is the largest crossing rather than the first.
The guidelines expire on 31 December 2026. Reclamation published the Final Environmental Impact Statement for post-2026 operations on 31 July, setting out an adaptive framework running to 2036 with Lower Basin shortage reductions of up to 3.0 million acre-feet — far beyond anything the 2007 tiers contemplated. Until a Record of Decision is signed and that framework takes effect, the arithmetic that connected an August projection to a January delivery cut has no successor in force.
Which gives this month’s study an unusual status. Every August study since 2007 has determined the following year’s shortage tier on publication. The August 2026 edition is the first that will not, because the instrument that gave its number legal effect runs out before the year it would have governed begins. As of Sunday evening the study had not appeared at the address Reclamation’s own archive uses for it; the July edition remains the most recent published.
None of this changes the water in the reservoir. Lake Mead stood at 1,039.76 feet on Reclamation’s daily gauge, and the operational questions the studies exist to answer — how much comes through Glen Canyon, what Powell holds back — are being decided in the environmental review rather than by a threshold in a table. But the projection will keep being published monthly, and it will keep being read as though it triggers something.