Most of Lake Powell's inflow originates as summer snowmelt from the Rocky Mountains of Colorado, Utah and Wyoming. Releases are made over a water year of October 1–September 30, due to the fact that the annual snowpack begins to accumulate in late autumn. On April 1 of each year, the Bureau of Reclamation releases its official forecast of the April–July (snowmelt season) runoff, and adjusts releases from Glen Canyon Dam accordingly to maintain Lake Powell at a safe level. An accurate forecast is vital to prevent uncontrolled spilling, which would waste water that could have been used for power generation. Although the snowpack typically reaches its peak and begins to melt in April, the picture can occasionally change unexpectedly and dramatically – either due to a hot and dry spring that evaporates snow before it can melt, or an extremely wet spring as occurred in May 1983. After the near disaster in 1983, the USBR has maintained a minimum of of flood-storage space in Lake Powell at the beginning of each year, to guard against unanticipated high runoff.