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From first snowflake, 'water year' is long and important

Apr 28, 2014 - By Eric Blom, Staff Writer

The first snowflake of the "water year" drifted down sometime on Sept. 25 and settled on Togwotee Pass. More followed, falling thick and fast to pile up and blanket the upper Wind River Mountains with the beginning of the winter's snowpack.

This is where nearly all of Fremont County's water starts.

It ends spread on farm fields, filling a trough for livestock, spraying from a lawn sprinkler, filling a bathtub, or passing all the way through the Wind River Basin, Boysen Reservoir and out of the county.

The water staying in the waterways provides a habitat for aquatic life and recreation for people.

Other snow melts off the south side of the Wind Rivers into the Sweetwater River where to bring water to wildlife and a string of ranches along its course.

Because the snow is so vital, many people and machines spend all winter watching how it accumulates on peaks circling the southern, western and northern sides of the Wind River Valley.

Machines

At midnight that September night, a snow telemetry machine, or SNOTEL, on the pass came to life all by itself to take its daily recording. Snow for the first time in three months covered the SNOTEL's fluid-filled pillow and pushed the liquid up a tube inside the machine, where a sensor recorded its height. The machine used that measurement to determine the snow's weight and the amount of water it contains.

Then, an antenna hanging over the pillow shot a radar signal toward the ground and measured the snow's depth at 10 inches.

After collecting its data, a very high frequency radio antenna on the SNOTEL shot it out to space.

At about 50 to 75 miles up, the signal hit a layer of the atmosphere left ionized by meteors that burned up entering the atmosphere, and the radio waves bounced back toward earth and receivers, allowing the Natural Resources Conservation Service to compile the information.

Nine other SNOTELs humming along in the Wind River Basin performed the same measurements and transmitted their data back to NRCS, along with two on the Little Wind River, two on the Sweetwater River and six above the Popo Agie River. Hundreds more are scattered throughout mountains in Wyoming and 12 other states.

Snow courses

Other data collection is hands on.

Once a month from January through the spring, workers with the Wyoming State Engineer's Office in Riverton take a break from crunching last year's runoff data and mount snowmobiles. Over four or five days, they travel to six spots, called snow courses, above Lander and eight others near Dubois to study the snow manually.

At each snow course, the workers drive thin metal tubes into the snow and pull up core samples. They measure the height of the snow in the tubes, and then weigh the tubes to determine how much water is in the snow.

"They're not so much measuring we've got 70 inches of snow, we're measuring we've got 30 inches of water," State Engineer's Office division superintendent Loren Smith said. "That relates directly back to we're expecting so much runoff."

The State Engineer's Office has sampled snow at each course in the same five spots month after month, year after year for decades. The locations are kept the same so data can be compared over time.

Accumulation

This year, both humans and machines have had more snow than usual to measure.

Several snow storms buffeted Fremont County in the 2013-2014 winter, dropping snow on the Wind River, Owl Creek and Absaroka Mountains.

Those systems often bring precipitation to lower parts of the county as well. From September through March, Riverton saw 38 days of rain and 67 of snow.

October through January saw the snow pack climb steadily until it spiked upward from February through March. By the beginning of April, the snow was 103 inches deep on Togwotee Pass, and a SNOTEL on South Pass measured 59 inches.

Across the Wind River Basin, the snow held on average 15 inches of snow-water equivalent, meaning the amount of water the it would melt into. That amount was 30 percent more water than average, portending a wet spring.

"We should have good runoff," said NRCS water supply specialist Lee Hackleman.

Reporting

Every week during the winter and into the spring, Hackleman produces the Monday Morning Snow report for Wyoming. It collects data from SNOTELs and snow courses from across the state and shows the how the average snow water equivalent in each basin compares to historical medians.

His office also sends its data to NRCS forecasters in Portland, Ore. At the beginning of each month from January through June, the Portland office produces a prediction of how much runoff to expect in each Wyoming basin.

The NRCS expects the Wind River to run higher than normal this spring and summer, according to the most recent report, but so far the Sweetwater looks like it will run slightly below average.

Using the data

The National Weather Service looks at snowpack to see how it affects climate conditions, such as flooding and drought.

"We're trying to predict what we think the high flow is going to be for runoff especially for flooding to give people some time if water's going to be high," NWS hydrologist Jim Fahey said.

He has been following NRCS's snowpack data and believes it is a good start, but precipitation through the spring will have a big impact on the amount of runoff later. Fall storms brought high levels of soil moisture in the upper Winds, which should lead to more water in streams and rivers.

"Not much more should percolate into the ground, and there should be more runoff," he said.

The lower Winds did not freeze as soon, and the soil had more time to dry out before winter, so runoff will be able to soak into the ground more in those areas, Fahey said.

Peak runoff

If past years are any indication, snowpack in the Wind River basin should continue to climb for a week to a month before peaking. Then, the runoff will being in earnest, itself reaching its maximum in May or June.

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Next: Follow the water as it melts and meet people affected by it.

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