NRCS: February Colorado Basin Outlook Report

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Hot off the presses here’s the February Colorado Basin Outlook Report from the Natural Resources Conservation Service. Here’s the summary:

Summary

Colorado experienced a dry month during January, with extremely dry conditions in portions of southwestern Colorado. Snowpack percentages have decreased from those of a month ago in all basins of the state. Given the excellent start to the year, snowpack percentages still remain above average nearly statewide. January was the driest month of the water year with precipitation totals well below average in most basins. As expected, runoff forecasts have decreased from those issued a month ago. The state can now expect below average runoff this summer across all of the southern basins. While the water supply cushion we developed after the December storms has eroded, much of the central and northern basins can still expect near to above average spring runoff. Reservoir storage continues to track near average in most basins.

Snowpack

What a difference just a month makes. After experiencing abundant snowfall during late December, the western storm track left most of Colorado high and dry during January. The driest basins were in southern Colorado where the combined San Juan, Animas, Dolores, and San Miguel basins decreased by 38 percentage points from last month and are now standing at 106% of average. Snowpack statistics in the Gunnison basin closely followed, decreasing by 32 percentage points and is now 126% of average. The monthly decreases were large enough in the Rio Grande basin to decrease the percentages to below average levels, now at only 80% of average. Colorado’s statewide snowpack dropped significantly this month; down from the January 1 totals of 136% of average to 117% of average on February 1. Even after such a dry month, above average snowpack totals prevail across most of the state. The highest percents of average remain across northern Colorado, where percentages that exceed 130% of average can be found in the Colorado and North Platte basins. Colorado’s eastern basins faired the best during the dry January, with only slight decreases recorded in the Arkansas and South Platte basins. The best snowpack news for this month is the comparison to last year’s February 1 snowpack totals. This difference is most striking across the northern basins where percents of last year remain well above those of last year, and is an impressive 188% of last year in the Colorado Basin. While this expresses this year’s abundance, it also reflects last year’s dryness in this basin. Statewide snowpack totals are now at 137% of last year’s February 1 readings.

Precipitation

Monthly precipitation during the 2011 water year has been on a rollercoaster with wet months followed by dry months. Fortunately, statewide totals for the three months of October through December were all above average, leaving January’s totals as the only month with below average percentages. Monthly totals of only 23% of average were recorded during January in the Rio Grande Basin, which was the lowest basinwide percentage in the state. Only the South Platte Basin recorded an above average total for the month, at 106% of average. Statewide precipitation measured at SNOTEL sites across Colorado was only 73% of average in January. For the four months comprising the water year, percentages range from 133% of average in the Yampa, White and North Platte basins to only 85% of average in the Rio Grande Basin. Statewide water year totals decreased by 18 percentage points this month and are now at 121% of average. These readings remain well above last year at 137% of those totals.

Reservoir Storage

As is typical during mid-winter, reservoir storage changed only slightly during January. Storage volumes are near to above average in all basins, with the exceptions of the Yampa, Arkansas and Rio Grande. The lowest, in terms of percent of average, is the Rio Grande Basin which now stands at 79% of average. In terms of storage volume, the lowest departure from average storage is in the Arkansas Basin, currently storing 91% of average volumes, or a deficit of 50,000 acre-feet. Only the Rio Grande and Arkansas basins are storing significantly less than last year at this time, at 85% and 91% of last year’s storage, respectively. The highest storage volumes remain in the Colorado and Gunnison basins this month, at 112% and 109% of average, respectively. With statewide storage now at 103% of average, volumes have exceeded the average mark by 90,000 acre-feet. This year’s statewide storage remains at 100% of last year’s volumes on this same date. Assuming inflows this spring and summer remain at or above average this year, late summer water supplies should be adequate for most water users across the state.

Streamflow

As one would expect after such a dry month, runoff forecasts have decreased across Colorado. While at least the northern basins can continue to expect above average summer water supplies, the greatest concerns remain across the southern basins which now are expecting below average runoff. The lowest forecasts continue to be along those streams originating in the Sangre de Cristo Mountains, where volumes of only 40% to 80% are expected. This month also saw runoff forecasts decline sharply in the headwaters of the Rio Grande and San Juan Rivers. Flows on those rivers are now expected to be consistently below average for the 2011 runoff season. These basins will need a significant turnaround in weather patterns over the next few months in order to see improvements in this year’s water supply outlook. Meanwhile, across most of central and northern Colorado the water supplies remain quite favorable. Above average volumes are forecast throughout the Colorado, Yampa, White, North Platte and most of the South Platte basins in 2011. As usual, continued snowfall is critical for maintaining these expectations, so monitoring the snowpack will be critical through the remainder of the winter.

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