Ag Weather Forum

Variable Western Water Forecast

Bryce Anderson
By  Bryce Anderson , Ag Meteorologist Emeritus
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Following are highlights of the March USDA Western Snowpack and Water Supply Conditions report. There is some improvement on snow pack and water supplies in the Rocky Mountains, but the Far West--Cascade Mountains and Sierra Nevada Mountains--remain well below normal, along with the southwestern U.S. The full report with graphics is at this link: http://tinyurl.com/…

Bryce

Twitter @BAndersonDTN

Precipitation during February was near to somewhat below normal in northern areas and central Alaska, whereas it was generally quite dry in southern areas and coastal Alaska. Thus far in the water year (beginning October 1, 2014), precipitation has been near or somewhat above normal in the northern and eastern parts of the West and coastal Alaska, with southwestern areas and interior Alaska being fairly dry. Snowpack shows sharp contrasts between the low levels in southwestern and far western areas and near to above normal levels along the Rocky Mountains and in interior Alaska. Streamflow forecasts are generally below normal, except along the Rocky Mountains and in northern Alaska, where the outlook is near normal. Reservoir storage is currently below normal in the Southwest and near to above normal elsewhere.

Streamflow forecasts are moderately to extremely below normal for most of the West. The only areas of near normal forecasts are the Rocky Mountains, extending from central Colorado northwest into British Columbia, and in central and northern Alaska. In western Washington and Oregon, despite snowpack being at record lows, most forecasts are only moderately below normal in terms of percent, but these are actually at the very low end of the historical range of streamflow.

State-By-State Summaries:

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Arizona: Recent storms have mostly benefitted the Verde River Basin, which is now forecast at near normal streamflow for the spring. The storms produced a total of about four inches of precipitation over this basin, saturating the soils, and resulting in significant early runoff in the Verde and its tributaries.

California: Some precipitation was received during the month of February, mostly in the form of rainfall, while the existing snowpack continued to dwindle due to warm temperatures. Fortunately though, water levels in the major storage reservoirs showed a slight increase due to runoff from the storms and the low water demand during this time of the year.

Colorado: Two weeks of wet weather through the end of February and beginning of March have provided a significant increase in snowpack throughout Colorado and an even greater boost to those southern Colorado basins that are still ailing after several consecutive years of below normal snowpack. Despite substantial accumulations statewide, snowpack has not quite returned to normal at 87 percent on March 1.

Idaho: Warm February temperatures and rain combined to take its toll on Idaho’s snowpack. Snowpacks across southern Idaho increased from west to east ranging from only 28 percent in the west to 115 percent in the east. The snowpack also increases going north but drops to half of normal in the Panhandle Region.

Montana: Snowpack percentages dropped for the second month in a row due to above average temperatures, lack of significant snowfall, and rain-on-snow events.

Nevada: Snowpack is at record low levels at 32 stations. Summarizing over basins, five -- Lake Tahoe, Lower Humboldt, Upper Humboldt, Eastern Nevada, and Owyhee -- have record low snow. Unless Nevada has a “miracle March” as in 1991, the drought’s effect will continue to worsen.

New Mexico: Snowpack is well below average as the end of the main snow accumulation season in the mountains approaches. The prospects for a decent spring snowmelt runoff across New Mexico continue to hinge on the future storm track.

Oregon: Oregon’s mountains have received near normal precipitation since the water year began on October 1, but the snowpack is well below normal as of March 1. Warm temperatures during the majority of this year’s storms resulted in more rain than snow in the mountains. As of March 1, 45 percent of Oregon’s long-term snow monitoring sites are at the lowest levels on record, and 68 out of 153 snow monitoring sites across the state are snow-free, which is highly unusual for March 1. There is a high likelihood that Oregon’s streams and rivers will have below normal flows this summer given the current state of the snowpack.

Utah: February was long, hot, and dry. Water supply conditions have declined, and with only one month left in the snow accumulation season, Utah is not likely to see substantive improvement.

Washington: Essentially no measureable snow accumulated throughout the month of February until the very last days of the month when areas above 4000 feet elevation received a light dusting. More than 27 percent of the SNOTEL and snow course network sites set new all-time record low or near record low snow water equivalent for March 1. Total precipitation was near normal for the month; however, temperatures were 4-10 degrees above normal.

Wyoming: Snowmelt runoff projections indicate that statewide, approximately 90 percent of average spring and summer streamflow is expected.

(ES/SK/AG)

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