Tuesday, April 6, 2010

Snowpack improves, but below normal

Wet Spring to the Rescue! Snowpack Improves

Boise--Idaho Farmers have dodged the bullet, A series of spring storms have rocked Southern Idaho with rain in the valleys and fresh snowpack with some mountain locations reporting more than two feet of fresh snow, but is it enough? April 1st marked the official start to the irrigation season.
“A slow defrost is what we need to help salvage this year’s water supply,” said Ron Abramovich, Water Supply specialist for NRCS. “A wet, cool spring would reduce and delay the irrigation demand, extending the limited water supply.”

Abramovich tested the snowpack in the Mores Creek area near Idaho City a few days ago and says the snowtel sights reflect moderate gains of critical water content and new snowpack. The storms have dropped between 1-4 inches of water content, but not enough to solve the water supply shortages that will occur in most drainages.

"We're trying to verify what's being reported hourly versus what's actually on the ground up here," said Abramovich. Snowpacks across Idaho range from 50 to 75% of average and have peaked with runoff now in full swing. Cool temperatures have delayed snowmelt with wet soil has meant less demand for irrigation water.

As summer approaches, the information gathered is extremely important for farmers and those dependent on water planning for the next year. "If we can more accurately forecast it, users can plan ahead whether they're going to have too much, or too little water like this year the way it's shaping up to be," Abramovich said. Despite recent snowfall in the mountains, the findings from their research shows that Idaho is still coming up a bit short on water.

Boise Basin sites are 71 percent of average, the good news is that they’re still gaining snowpack, temperatures are cool and valley soil is wet and won’t need much recharge.

Eighty percent of all the precipitation in Idaho comes in the form of snow. That's why hydrologists say it's so important to keep an eye on the numbers.

"With the snowpack 30 percentage points below average, we're going to expect and see below-average stream flow this year," Abramovich said. "It's going to be tough to fill the reservoirs, so the reservoir operators will be monitoring it pretty closely."

Yet the current storm track is favoring farmers although many would rather be in the fields that watch the rain fall. Boise Watermaster Rex Barrie regulates all the water flow in the Boise Basin, he’s keeping a close eye on the series of storms and snowpack.

"We're concerned about the reservoirs filling this year," Barrie said. "This is good news, this extra snow. A couple inches of water helps, every little bit helps, but we're still concerned."

Hydrologists say we should have enough water to make it through this season because of current water levels, but next season could be a different story.

"This year we probably have enough water to make it through the season, but it will leave us in a short supply at the end of the water season," Barrie said. "So, if we have a back-to-back short water year as far as snowpack goes that puts us into next year with the question, do we have enough water to make it through the irrigation season?"
Here is a summary of the Water Supply Outlook by region:

Panhandle Region – The end-of-March precipitation boosted the monthly totals to 80 to 90% of average but won’t significantly change the water supply outlook as the snowpack is only about 50 to 75% of normal. The seasonal streamflow volume forecasts reflect the region’s below average snowpacks. Boundary and Smith Creeks and the Kootenai, Clark Fork, and Priest Rivers are forecast for 60 to73% of normal streamflow volumes. In the southern part of the region, the St. Joe, Spokane, Pend Oreille, and North Fork Coeur d’Alene Rivers are forecast at 42 to 50% of normal.

Clearwater River Basin – Even with the end-of-March precipitation, the Clearwater River Basin had one of its least snowy seasons keeping the water supply outlook for this basin poor. The snowpack as of April 1 is the third lowest in almost 50 years and south-facing and low elevation sites are already bare and dry. Steamflow forecasts range from 55 – 61% of normal. Limited flows into Dworshak Reservoir are expected; it is currently 67% full and is not expected to fill this spring.

Salmon River Basin – Overall, the Salmon River Basin snowpack is 64% of average. Streamflow forecasts for the Main Salmon and its tributaries are at 50% of average. In other years with similar snowpacks, the Salmon River at White Bird peaked at 25,000 to 35,000 cubic feet per second between May 1 and June 1. Water uses and river runners should expect a similar streamflow pattern this year. The Middle Fork Salmon River will have a short high water season unless a wet spring occurs. The Salmon River will see a very long floating season with a short high water season.

Weiser, Payette, Boise River Basins – Late March storms increased the monthly precipitation total to 86% of average for the region. The April 1 snowpacks measure around 65% of average in the Payette and Boise Basins and 78% in the Weiser Basin. Streamflow forecasts range from 55 to 70% of average.

Wood and Lost River Basins – Precipitation during the last three days of March greatly improved the month’s precipitation total but it was too little to rescue the summer water supply outlook for these basins. The snowpack for April 1 ranges from 60 to 75% of average with the lowest snowpack in the Little Lost Basin. Forecasted streamflows range from 40% of average for the Big Wood River above Magic Reservoir and Camas Creek near Blain to near 60% of average for the Big Wood River at Hailey, and the Little Lost and Big Lost Rivers.

Upper Snake River Basin – This has been one of the driest winters on record for this basin. March recorded just over half of the normal monthly precipitation putting the total precipitation since October 2009 at 61% of average. Reservoirs are storing as much as they can in this low snow year. Streamflow forecasts range from 20 to 60% of average. Water shortages are nearly certain based on the current snowpack levels.

Southside Snake River Basins – The water year-to-date precipitation for this region is at about 83% because this region benefitted from being on the northern edge of the El NiƱo storm pattern. Snowpacks range from 74% of average for the Salmon Falls basin to 114% of average for the low elevation Owyhee basin. Owyhee streams combined with reservoir storage should be adequate to meet irrigation supplies. While shortages are expected for the Salmon Falls and Oakley basins. A wet spring could help overcome the water deficits.

Bear River Basin – This winter, most of the storms missed the Bear River Basin. The water year-to-date precipitation is 65% of average with March precipitation being only 56% of normal. Even with the April 1 snowpack at 60% of normal, water stored in Bear Lake combined with Bear River’s the predicted streamflow of 16% of average will be enough for irrigators to squeeze through the year.

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