NRCS: The May 1, 2014 Colorado Basin Outlook Report is hot off the presses

streamflowforecastmap05012014nrcs

Click here to read the report. Here’s an excerpt:

Summary

When viewing current statewide totals for all water supply parameters, it would be difficult to find a more “normal” year. With statewide snowpack, water year-to-date precipitation and reservoir storage at 107, 102 and 93 percent normal respectively, conditions are favorable for good water supplies this season. Of course the story is more complex than just the statewide numbers. Although 2014 was not a La Nina year some of the snow accumulation patterns could be construed as such the Upper Rio Grande and the combined San Juan, Animas, Dolores and San Miguel basins in Colorado both have snowpack percentages below 70 percent of median, while significantly better snowpack’s exist in the northern tier basins. All of the northern basins boast snowpack percentages that are greater than 120 percent of median. In general the statewide snowpack trended downward over the course of April falling 8 percentage as a result of below average precipitation in the form of snowfall throughout the month. Although monthly precipitation for the state was just 80 percent of average this April, year-to-date precipitation rounded out at 102 percent of average on May 1. With nearly all reservoirs currently at better standing than last year at this time, it is hard to frown upon the below average storage in the Upper Rio Grande and Arkansas River basins. In addition the vast majority of water supply forecasts for Colorado look to be better than last year based on current data.

Snowpack

Despite a slight decline in the snowpack percent of median during April, statewide snowpack was still 128 percent of last year according to SNOTEL and snow course observations on May 1. The Upper Rio Grande saw the greatest decline in snowpack with a 29 percent drop this month. All major basins saw a decrease this month, yet many remain near to above normal while some are well above normal. With nearly one third of all sub basin snowpack’s at 125 percent of median or better and 19 of 34 sub basins above 100 percent of median, this season is just what was needed to replenish last year’s ailing water supplies in the state’s northern watersheds. In the other regions of the state, the Arkansas and Gunnison basins are fortunate to have snowpack’s at 99 and 97 percent of median respectively, while the “have not” basins include the Upper Rio Grande and the combined San Juan watersheds at 50 and 68 percent of median respectively. The moral of this snow season is: snowpack varies greatly across the state, from 41 percent of median in the combined Conejos & Rio San Antonio watersheds to 169 percent of median in the Muddy Creek drainage in the Colorado River basin. Be sure to look at basins of interest and the sites within for the most concise data to prepare for the year to come.

Precipitation

For the first time since January, monthly precipitation was below average, not just statewide, but in every major basin. Quite similarly to January when monthly precipitation was at 81 percent of average, precipitation this month was 80 percent of average. Thanks to strong accumulations in October, January, February and March, year-to-date precipitation remains slightly above normal at this point. Thankfully the differences in year-to-date precipitation across the state are not as extreme as in the case of snowpack. The Upper Rio Grande basin has the lowest year-to-date total at 80 percent of average, with the only above average month this water year being November. Conversely, the South Platte basin is currently showing year-to-date precipitation at 119 percent of average. In general the precipitation map looks much the same as the snowpack map with better totals in the northern basins, and below average numbers in the south.

Reservoir Storage

With over one half of the states reservoirs currently at 100 percent of average storage or better, and nearly three quarters of the state’s reservoirs at or above 80 percent of average at the end of April, statewide reservoir storage is in fairly good standing. The Arkansas River basin currently has the lowest storage as a percent of average at 59 percent but on a positive note Pueblo Reservoir is right at the 30 year average storage with volumes at 54 percent of capacity. The South Platte River basin has the best storage at 110 percent of average and 90 percent of capacity. With the snowpack in the basin this year it is likely the South Platte reservoirs will reach 100 percent capacity this spring. The vast majority of all reservoirs in the state currently have higher storage levels than at this time last year. For areas with well above normal snowpack’s and projected streamflows, it is often necessary to draft reservoirs to make room for the above normal expected inflows. If reservoir storage is below average in a drainage basin with above to well above normal snowpack the project may be anticipating above average inflows.

Streamflow

Projected streamflows in Colorado are typically a reflection of current snowpack totals and monthly precipitation totals throughout the year, and this month is no exception. Similar to the snowpack reports current forecasts vary widely across the state from 148 percent of the May to July average for the Inflow to Wolford Mountain Reservoir to 16 percent of the May to September average at San Antonio River at Ortiz in the Upper Rio Grande. For the three major watersheds in the north, nearly all streamflow forecasts are calling for above normal runoff this season. Within that same region only three forecast points have forecasts below average; all other points look to have strong water supplies going into the beginning of summer. On the flip side of the state, in the four major southern basins, just over one quarter of the forecasted streamflows are projected to be 100 percent of normal or better. Brightening the scenario further in the south, 24 of the 55 forecast points are projected to be better than 80 percent of average. But with highly variable snowpack across the state forecasts differ greatly as well, be sure to consult the actual forecast information for the most accurate information.

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