NRCS: The June 1 Basin Outlook Report is hot off the presses


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


As is fairly typical during the springtime in Colorado, May weather patterns brought a taste of nearly every season to our great state. A large snow storm over Mother’s Day weekend produced significant accumulation in every major river basin and stalled the rapid melt that had begun early in the month due to warm temperatures. Colorado also received significant precipitation in the form of rain during May, in fact for the first time this water year, all basins reported above normal monthly precipitation totals. During the last week of May, temperatures across the state exceeded historical averages for multiple days in a row. In the northern and central mountains, which had significant amounts of snow remaining, the high temperatures accelerated snowmelt. This coupled with heavy rainfall, led to high water levels on many rivers and flooding in some areas. With above average streamflows projected for June and July in the northern and central part of the state, water managers in these regions will have ample opportunities to fill their reservoirs this season. In the southern part of the state storage volumes remain low and with most of the snow already gone hopes are pinned on a good monsoon season.


The statewide snowpack totals this season were a welcome change from the last couple of years. This season began with fairly normal snow accumulation up until early February when a series of large storm systems began to hit the state. The storm systems generally favored the northern and central mountains and for the most part missed the mountains in the Southwest, the Upper Rio Grande and the southern tributaries of the Arkansas. The storm patterns continued until the first week of April when most of the basins in the state reached their peak snow accumulation and melt ensued. April was quite dry across the state and it looked like winter may be over when the entire state received significant snow over Mother’s Day weekend. This storm added to the already large snowpack’s in the northern and central mountains but most importantly, boosted the snowpack’s in the southern river basins and helped to delay the rapid melt that had begun in those regions. As of June 1 the statewide snowpack was 197 percent of the median and around 25 percent of the seasonal snowpack remained on the ground.


For the first month this water year all the major river basins in Colorado reported above average mountain precipitation. Statewide precipitation for May was 135 percent of average; the Arkansas basin reported the lowest percentage at 115 percent of average and the South Platte basin had the highest percentage at 155 percent. As of June 1, water year-to-date precipitation totals across the major river basins were near to above normal. The Upper Rio Grande had the lowest percentage at 84 percent of average for the water year. The South Platte had the highest percentage at 124 percent of average. Year-to-date precipitation for the state was 105 percent of average on June 1.

Reservoir Storage

During May Colorado added 419,400 acre-feet of water to its reservoirs. The end of May readings put total storage at 95 percent of average and 62 percent of capacity. Of course storage varies significantly between the major river basins. The South Platte basin has the highest storage totals; with 1,041,600 acre-feet of water, basin wide storage is at 113 percent of average and 94 percent of capacity. The Gunnison basin is not far behind with storage volumes that are 108 percent of average and 80 percent of capacity. The Arkansas basin is storing the lowest volume of water as a percent of average. The basin has 351,100 acre-feet of water stored which is 56 percent of average and 21 percent of capacity. Current reservoir storage mimics the trends in snowpack and spring runoff seen this season across the state. The southern basins have much less water stored than the northern basins. It is important to note that all basins have significantly improved their reservoir storage since last year at this time. Storage in the Upper Rio Grande for example is at just 63 percent of average currently, but this is a great improvement over the 37 percent of average volumes they had last year.


One of the main variables that can influence streamflow forecasts drastically in the spring is how much rain an area receives. For the most part, the streamflow forecasts for Colorado issued on June 1 were very similar to those issued on May 1; the exceptions were forecasts for the South Platte, Colorado and the Yampa and White river basins. These regions received significant amounts of rain throughout May which caused the current forecasts to increase considerably from those issued last month. The South Platte forecasts were the most affected by this; the region was hammered with thunderstorm activity and heavy rains throughout the month. The forecasts for the Cache la Poudre at Canyon Mouth west of Fort Collins, CO saw the most drastic increase this month. April to July forecasts jumped from 122 percent of average predicted on May 1 to 167 percent of average on June 1. June to July forecasts for this gage call for flows at 150 percent of average. In the Colorado basin the forecast for April to July flows into Wolford Mountain Reservoir jumped 31 percentage points this month. The current June to July forecast calls for flows to be at 163 percent of average. Forecasts in the remaining basins did not change much from those issued last month. The Upper Rio Grande still has some of the lowest forecasted flows for the remainder of the summer. The southern tributaries of the Arkansas basin are also forecast to see flows that are well below normal for the rest of this runoff season.

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