|
<br />How Forecasts
<br />Are Made
<br />
<br />For More Information
<br />
<br />/' jl ~
<br />1'lJil
<br />
<br />Foreword
<br />
<br />Most of the annual streamflow in the Western United States originates as snowfall that has accumulated
<br />high in the mountains during winter and early spring. As the snowpack accumulates, hydrologists
<br />estimate the runoff that will occur when it melts. Predictions are based on careful measurements
<br />of snow water equivalent at selected index points. Precipitation, temperature, soil moisture and antece-
<br />dent streamflow data are combined with snow pack data to prepare runoff forecasts. Streamflow forecasts
<br />are coordinated by Soil Conservation Service and National Weather Service hydrologists. This report
<br />presents a comprehensive picture of water supply outlook conditions for areas dependent upon sur-
<br />face runoff. It includes selected streamflow forecasts, summarized snowpack and precipitation data,
<br />reservoir storage data, and narratives describing current conditions.
<br />
<br />Snow pack data are obtained by using a combination of manual and automated measurement methods.
<br />Manual readings of snow depth and water eQuivalent are taken at locations called snow courses on
<br />a monthly or semi-monthly schedule during the winter. In addition, snow water eQuivalent, precipita-
<br />tion and temperature are monitored on a daily basis and transmitted via radio telemetry to central
<br />data collection facilities. Both monthly and daily data are used to project snowmelt runoff.
<br />
<br />An error is associated with each forecast, and this error decreases as the season progresses and
<br />more data becomes available. To express the range of error that can be expected, "most probable"
<br />forecasts are issued along with a range representing a "reasonable minimum" and a "reasonable max-
<br />imum". Actual streamflow can be expected to fall within this range in eight out of ten years. Addi.
<br />tionally two specific scenarios are provided based on the assumption that subsequent precipitation
<br />will be "wet", above average, or ''dry': below average.
<br />
<br />Copies of Monthly Water Supply Outlook Reports and other reports may be obtained from the states
<br />listed below. An annual snow survey data summary is publiShed by the Soil Conservation Service
<br />for each of the western states. Historical snow survey data may be obtained at those same offices.
<br />
<br />"
<br />"I.
<br />: 'I'
<br /><L/
<br />
<br />STATE ADDRESS
<br />Alaska 201 East 9th Ave., Suite 300, Anchorage, AK 99501.3687
<br />Arizona 201 East Indianola Ave., Suite 200, Phoenix, AZ 85012
<br />Colorado 2490 West 26th Ave., Buildin9 A, 3rd floor, Denver, CD 80211
<br />Idaho 3244 Elder Street, Room 124, Boise, 10 83705
<br />Montana 10 East Babcock, Room 443, Federal Building, Bozeman, MT 59715
<br />Ne....ada 1201 Terminal Way, Room 219, Reno, NV 89502
<br />New Mexico 517 Gold Ave. S.w.. Room 3301, Albuquerque, NM 87102-3157
<br />Oregon 1220 Southwest 3rd Ave., Room 1640, Portland, OR 97204
<br />Utah 4402 Federal Building, 125 South State Street, Ssll Lake City, UT 84147
<br />Washington W. 920 Riverside, Room 360, Spokane, WA 99201-1080
<br />Wyoming Federal Building, 100 "B" Street, Room 3124, Casper, WY 82601
<br />In addition to state reports, a Water Supply Outlook for the Western United States is published by
<br />the Soil Conservation Service and National Weather Service monthly, January through May_ Reports
<br />may be obtained from the Soil Conservation Service, West National Technical Center, 51t Northwest
<br />Broadway, Room 248, Portland, DR 97209-3489.
<br />
<br />Water supply reports published by other agencies:
<br />
<br />California - Snow Survey Branch, California Department of Water Resources, P.O. Box 388, Sacramento,
<br />CA 95802; British Columbia - The Ministry of Environment, Water Investigations Branch, Parliament
<br />Buildings, Victoria. British Columbia, V8V 1X5; Yukon Territory - Department of IndIan and Northern
<br />Affairs, Northern Operations Branch, 200 Range Road, Whitehorse, Yukon Territory, Y1A3V1; Alberta,
<br />Environment Technical Services Division, 9820 106th St., Edmonton, Alberta T5K 2J6.
<br />
|