Lake Mead would sink to about 1,006 feet by September 2027 if the river stays dry

The Bureau of Reclamation’s driest planning case for the Colorado River’s lower reservoir ends with Lake Mead at 1,006.43 feet above sea level on the last day of September 2027, about 31 feet below the 1,037.80 feet the same table records for the end of September 2026. The figure comes from the Probable Minimum run of the agency’s October 2026 24-Month Study, dated October 15. It is a dry-case scenario built to show how low the lake could go, not a forecast of where it will be.

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Nothing in the study says the lake is on that path today. A probable-minimum run assumes inflow low enough that, by the study’s own description, it would be exceeded 90 percent of the time, which makes it a planning floor rather than a central estimate. The same table also shows how much water the scenario removes: end-of-month storage drops from 6,827 thousand acre-feet in September 2026 to 4,844 thousand in September 2027, a loss of about 2 million acre-feet in twelve months.

A 24-month planning tool with three inflow cases

Reclamation keeps an archive of 24-Month Study reports that runs from 2010 to the present, and each month’s report is offered in Most Probable, Minimum Probable and Maximum Probable versions. The October Minimum Probable report, processed on October 8 and dated October 15, gives its premise in a single line: “The Probable Minimum inflow scenario reflects a dry hydrologic condition.” That scenario is the one behind the 1,006.43-foot end-of-September 2027 elevation in the Hoover Dam table.

The nearer-term numbers are gentler. The study records Lake Mead at 1,037.80 feet at the end of September 2026, a month that closes with 6,827 thousand acre-feet in storage, and states that “Lake Mead’s elevation is projected to be 1,034.15 feet on December 31, 2026.” The lake then holds close to 1,033 feet through February 2027 in this run, so the long slide toward the September 2027 figure does not begin until spring.

Spring releases drive the drop to about 1,004 feet

The table shows where the decline comes from. Monthly releases through Hoover Dam rise from 448 thousand acre-feet in February 2027 to 905 thousand in March, 998 thousand in April and 1,016 thousand in May, while inflow in this dry case stays thin. End-of-month storage falls from 6,515 thousand acre-feet in February to 5,067 thousand in May, a loss of roughly 1.45 million acre-feet in three months, and the elevation drops from 1,033.17 feet to 1,010.21 feet over the same stretch.

The study’s total Hoover Dam release for water year 2027 is 8,124 thousand acre-feet. Evaporation is a smaller but visible line item, running between 19 and 46 thousand acre-feet a month across the 13-month table, and the table puts it highest in September 2026 and lowest in February 2027.

The lowest point in the run is not September. Lake Mead reaches 1,003.87 feet at the end of July 2027, after 1,017.48 feet in April and 1,005.04 feet in June, then edges back up to 1,005.88 feet in August and 1,006.43 feet in September as monthly releases ease to 651 and then 550 thousand acre-feet. The September 2027 figure is therefore a number on the way back up from a summer trough, which is a detail the single headline elevation hides.

Level 1 shortage now, a different footing in 2027

The lake already operates under a shortage. Reclamation’s August 15, 2025 announcement of 2026 operating conditions placed Lake Mead in a Level 1 Shortage Condition, based on an expected January 1, 2026 elevation of 1,055.88 feet. That determination called for Arizona to give up 512,000 acre-feet, about 18 percent of its annual apportionment, Nevada 21,000 acre-feet, or 7 percent, and Mexico 80,000 acre-feet, or 5 percent of its allotment.

The 2026 condition was set from a projection that placed the January 1, 2026 elevation between 1,050 and 1,075 feet, and the lake has since slipped under that band: the study’s table starts at 1,037.80 feet in September 2026. Calendar year 2027 is governed by new rules, though. The October Most Probable 24-Month Study says that “a shortage condition consistent with Section 5.3.A will govern the operation of Lake Mead” under the 2027-2028 operating guidelines, and it does not name a tier. That run puts Lake Mead at 1,034.52 feet on December 31, 2026 and 1,010.85 feet in September 2027, only 4.4 feet above the dry case by the end of the period.

The gap between the two cases is small at the end of 2026, about a third of a foot, and widens through 2027 as the two cases diverge. That spread is a measure of how much of the 24-month outlook rests on a few months of inflow that have not happened yet.

Where the lake stands now is a separate matter. Reclamation’s daily reservoir level report showed Lake Mead at 1,038.03 feet on October 25, 2026, with a note that the automatic readings had not yet been checked for errors. That is about a quarter of a foot above the study’s September 2026 end-of-month figure, so the lake sits close to where the dry case’s table begins.

The Minimum Probable table ends with 1,006.43 feet at the close of September 2027, and the study itself does not declare what that elevation would mean for any state or city. The next monthly report will update the starting point, and the answer to how dry the next 12 months turn out will come from inflow, which no table can supply.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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