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Limited Western U.S. Snowpack Forecast

Bryce Anderson
By  Bryce Anderson , Ag Meteorologist Emeritus
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A snow pack depiction map from USDA shows most western U.S. river basins have below to much below normal snow pack. (USDA graphic by Nick Scalise)

There's not a whole lot of snow for streamflow supplies in the western U.S. as of mid-January. Forecasts are decidedly mixed when it comes to particularly west of the Continental Divide looking ahead to the rest of this winter. Here's a USDA description of the situation.--Bryce

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WASHINGTON, January 15, 2015 -- A normal water supply is predicted for much of the West, while the Southwest, Sierra Nevada region and Pacific Northwest are beginning the year drier than normal, according to data from the first 2015 forecast of USDA's National Water and Climate Center (NWCC). California, Arizona and New Mexico as well as parts of Colorado, Utah and Nevada are experiencing prolonged drought, focusing attention again on the winter snowfall.

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"Right now, snowpack and streamflow forecasts look pretty close to normal for much of the West," NWCC hydrologist Cara McCarthy said. "A couple of major regional exceptions are the Southwest and California, which are unusually dry, once again."

In Western states where snowmelt accounts for the majority of seasonal water supply, information about snowpack serves as an indicator of future water availability. Streamflow in the West consists largely of accumulated mountain snow that melts and flows into streams as temperatures warm in spring and summer. NWCC scientists analyze the snowpack, air temperature, soil moisture and other measurements taken from remote sites to develop the water supply forecasts.

Overall, the basins of the Missouri, Colorado and Columbia rivers are expected to receive near normal streamflows.

In the Pacific Northwest, although rainfall during the fall months has been above average, the current snowpack is far below normal because of higher than normal temperatures.

"This is just the first forecast of the season; everything can change," McCarthy said. "A weak El Niño is forecast for this year, which might play a part in coming months."

Although variable, El Niño conditions tend to deliver more than normal winter precipitation to the Southwest and less to the Pacific Northwest.

In the West, the SNOTEL precipitation percent of normal map shows substantial precipitation in Montana, Wyoming, and New Mexico so far in January (blue areas). Above normal precipitation is also reported in one basin in southern Utah, and one basin in central Arizona (light blue areas).

Below normal precipitation is located across most of Washington, Oregon, California, Nevada, Idaho, northern and southwest Utah, southern Wyoming, Colorado, and northern New Mexico.

(ES)

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