Warm temperatures in late April resulted in widespread snowmelt across Idaho, the May 1 water supply outlook reports.
Natural Resource Conservation Service personnel said the above-normal snowpack in nearly all of the state is melting, and in some places melting too rapidly. That’s meant flooding in parts of southcentral and southeast Idaho and flood risk management efforts being taken at reservoirs around the state. Water has been released from some reservoirs to make room for snowmelt. Mackay Reservoir was listed at 43 percent full on May 1, which is 62 percent of normal.
Streamflows are above normal in many places and rainfall that’s already been abundant in May could prompt more river flooding, the report states.
In spite of plenty of snow this winter and a wet start to spring, most of Idaho is still considered abnormally dry. “After multiple years of drought conditions, it will take time to fully recover,” State Conservationist Curtis Elke wrote.
April precipitation varied across Idaho basins with no discernable pattern, he said. The Salmon, Lost, Wood and Central basins all saw near or above-normal April precipitation.
Total water year precipitation on May 1 showed the same pattern that’s been in place all winter. Northern Idaho is dry, averaging 79 percent of normal precipitation. The West-Central basins are at 98-110 percent of normal. The Lost and Wood basins range from 111 to 131 percent of normal. The Upper Snake sits between 114 and 142 percent of normal. The Bear River basin received 142 percent normal precipitation. The Raft River basin is at 132 percent of normal and the Owyhee basin is at 113 percent of normal.
April precipitation in the Lost and Wood basins was normal, ranging from 85 to 105 percent of normal amounts. “Basin snowpack is spectacular,” the report states, with all Lost and Wood basins between 145 and 200 percent of normal for May 1.
The Salmon River basin’s water year total precipitation measures 99 percent of normal, according to the report. Snowpack on May 1 in the Salmon basin still stood at 128 percent of normal. Peak snowpack this winter in the Salmon basin exceeded the 30-year median peak at 113 percent, Elke wrote.
Streamflow forecasts in the Salmon basin are normal and range from 95 to 120 percent of normal. However, the Lemhi River has more water with a predicted streamflow of 145 percent of normal through September.
Streamflow through September is expected to be well above normal in the Lost and Wood basins, ranging from 140 to 280 percent of normal, with the highest levels in the Wood basin.
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