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Mon, Sept. 21

Lake Powell at 45 percent capacity

November was a "dry" month in the upper Colorado River basin. Prior to a storm that reached the basin on the final day of November, snowpack was extremely low - only 35 percent of average. The storm boosted the average to 71 percent as of the beginning of December.

Inflow to Lake Powell is 9,800 cubic feet per second (cfs). Total unregulated inflows in October and November were 85 and 73 percent of average, respectively.

April through July unregulated inflow to Lake Powell in 2007 was 4.05 million acre-feet, only 51 percent of average. Water year inflow to Lake Powell for 2007 (October 2006 through September 2007) was 68 percent of average.

The elevation of Lake Powell as of last week is 3,598.3 feet with 11.59 million acre-feet of storage (48 percent of capacity).

The water surface elevation of Lake Powell will likely decrease between now and next March. The projected elevation of Lake Powell on Jan. 1 was 3,594 feet.

The Upper Colorado River Basin is experiencing a protracted multi-year drought. Since 1999, inflow to Lake Powell has been below average in every year except one.

In the summer of 1999, Lake Powell was essentially full with reservoir storage at 23.5 million acre-feet, or 97 percent of capacity. Inflow to Lake Powell in 1999 was 109 percent of average. The manifestation of drought conditions in the Upper Colorado River Basin began in the fall months of 1999. A five year period of extreme drought occurred in water years 2000, 2001, 2002, 2003 and 2004 with unregulated inflow to Lake Powell only 62, 59, 25, 51, and 49 percent of average, respectively. Lake Powell storage decreased through this five-year period, with reservoir storage reaching a low of 8.0 million acre-feet (33 percent of capacity) on April 8, 2005.

Drought conditions eased in water year 2005 in the Upper Colorado River Basin. Precipitation was above average in 2005 and unregulated inflow to Lake Powell was 105 percent of average. Lake Powell increased by 2.77 million acre-feet (31 feet in elevation) during water year 2005. But as is often the case, one favorable year does not necessarily end a protracted drought. In 2006, there was a return to drier conditions in the Colorado River Basin. Unregulated inflow to Lake Powell in water year 2006 was only 71 percent of average.

Water year 2007 was another year of below average inflow with unregulated inflow into Lake Powell at 68 percent of average. Over the past eight years (2000 through 2007, inclusive), inflow to Lake Powell has been below average in all but one year (2005).

Reservoir storage in Lake Powell and Lake Mead has decreased during the past eight years. Reservoir storage in Lake Powell is 48 percent of capacity. Storage in Lake Mead is also 48 percent of capacity.

Releases from Glen Canyon Dam in December 2007 will average 13,000 cubic feet per second (cfs) with a total of 800,000 acre-feet scheduled to be released for the month. On Mondays through Fridays in December, daily release fluctuations due to load following will likely vary between a low of 9,000 cfs (during late evening and early morning off-peak hours) to a high of 17,000 cfs (during daylight and early evening on-peak hours). On Saturdays and Sundays, release fluctuations will likely vary between a low of 9,000 cfs to a high of 16,000 cfs.

Releases in January are scheduled to be the same as December (800,000 acre-feet). The load following pattern in January will likely be very similar to December.

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