Monday, February 8, 2010
WATER SUPPLY OUTLOOK LOOKS BLEAK BASED ON IDAHO'S BELOW NORMAL SNOWPACKS AND STREAMFLOW FORECASTS
BOISE--Idaho’s snowpacks range from fair to poor according to snow survey data collected last week by the Natural Resources Conservation Service. The poor snowpacks across the state can be attributed to November, December and January’s minimal precipitation.
“The weather pattern this year is typical during El Niño years with good snow levels in the Southwest US and below normal levels in the Pacific Northwest.” said Ron Abramovich, Water Supply specialist for NRCS.
The best snowpacks are in the Owyhee basin at 95% of average and the lowest in the Coeur d'Alene, St. Joe, and Palouse basins at 50-55% of average. The snow in the Upper Snake River basin in eastern Idaho and western Wyoming is 60% of average, the fifth lowest in fifty years. Based on historic data, when the snowpack is this low on February 1, it does not recover to even near normal levels by April 1.
Water users can expect below normal runoff across all of Idaho. Current streamflow forecasts range from 45-80% of average and did not change much from volumes predicted in January because of the below normal January precipitation.
“The good news is that the reservoir storage is above average across most of the state and that will help buffer impacts of the below normal streamflows,” Abramovich added. “Water managers will monitor snow levels, inflows and spring weather closely when the melt season starts to ensure reservoirs fill as much as possible.”
Also good news, there is enough snow to have fun in! The snow depths are adequate for all types of winter recreation in the mountains. However, a hazardous weak layer in the snowpack persists and has resulted in four avalanche fatalities in Idaho so far this winter. More snow is needed to deeply bury this layer so it is less susceptible to sliding. Furthermore, more snow will provide much needed moisture for Idaho's numerous water users.
Here is a summary of the Water Supply Outlook by region:
• Panhandle Region – Snowpacks are below average across the region ranging from 50-85% of normal. This is a perfect model of the El Niño weather pattern – the southwest US has abundant winter moisture while the northwest tends to be dry. The low snowpack leads to less than optimal streamflow forecasts with the lowest flows predicted for the Spokane River at 45–50% of average and the highest for Clark Fork and Pend Oreille Lake Inflow at 80% of average.
• Clearwater River Basin – The Clearwater Mountains received snow recently but need a phenomenal amount of snow to bring the snow water content near average by April. Projected streamflow volumes will be low ranging from 55-65% of average. Dworshak Reservoir is storing near average amounts and will help supplement the lower summer streamflow levels.
• Salmon River Basin – The snowpack is only 69% of normal. The Salmon River and its tributaries are forecast to flow between 65-70% of their normal summertime volumes. Recreationists will still have a good season, but the duration of the high water season will be shorter with less snow to feed the river.
• Weiser, Payette, Boise River Basins - This region received almost near average precipitation in January which helped the snowpack in all three basins. The Weiser and Boise basins currently stand at about 83% of average while the Payette basin is 73% of average. Near normal precipitation the next two months will help to maintain a snowpack of 80% of average on April 1 which should be enough to meet surface irrigation water supplies in the valley. Good reservoir storage in the Boise and Payette reservoir systems will help irrigators and recreationists make it through the season despite the lower than normal snow.
• Wood and Lost River Basins - The best snowpack is in Camas Creek at 92% of average and the lowest snow is in the Big Lost and Little Lost drainages, both at 66%. The spring and summer streamflow volumes are predicted to range between 50-65%. The good news is that the current reservoir storage is 92% of average for Magic and 130% for Mackay reservoirs. However, the mountains need lots more snow or good spring rains like last year to offset any water shortages.
• Upper Snake River Basin - The entire Upper Snake River is in desperate need of more snow. Unfortunately, historical data shows there is little hope for snowpack recovery by April 1. The Upper Snake basin is experiencing one of its leanest winters since records began. An index combining 28 snow measuring sites in the basin above American Falls shows that this is the 6th lowest snowpack in 50 years. Reservoir storage is above average and will supplement low streamflow volumes. With current snow levels very similar to 2001 levels, a year when streamflows were only 47% of average, irrigators may need to use conservation practices implemented during other recent water short years.
• Southside Snake River Basin – Snowpacks improved as Southside basins picked up near average precipitation in January due to the El Nino weather pattern. Current streamflow forecasts call for 68% of average for Oakley Reservoir inflow, 50% for Salmon Falls Creek, and 59% in the Bruneau River. Irrigation water supplies should be marginally adequate in the Oakley and Owyhee basins while shortages may occur on the Salmon Falls tract.
• Bear River Basin – The recent snow in the Bear River high country at the end of January was not enough to boost the snowpack which is at 61% of average. Bear Lake is 38% full but despite the low levels of stored water, the size of this reservoir should provide adequate irrigation supplies even with limited inflows. The lack of inflows means the lake will be even lower by summer's end.
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