March conditions were much below average for both snow and precipitation every where except in the Bear Basin. Temperatures ranged from average to below average across northern Utah. Cool day time temperatures (below normal highs) helped sustain the average to above average snowpack conditions that accumulated from December through February. As of April 1, 2008 water supply conditions look good with both an average snowpack and average seasonal precipitation numbers leading into the runoff season. The only much below average precipitation numbers were the March monthly in the Weber, Six Creeks and Utah Lake areas which ranged from 56% to 67% of average. The Bear finished the month with below average conditions at 80% of average.

Short term guidance from National Weather Service Models indicates several storm systems during the next 9 days. This progressive pattern indicates active weather with no large scale ridge structures developing which leads to rapid warming and snowmelt. Instead we have average to slightly below average current temperatures and a cool short term forecast which will help in holding snow for several more weeks. This of course leads to the potential for more efficient runoff conditions when the weather finally turns warm. As of April 1st conditions across the Great Basin basin are good with normal snow and seasonal precipitation numbers to date.

Volumetric forecasts for the Great Basin ranged from 68% at Smith Fork nr Border on the Bear to 115% at Vernon Creek, West of Utah Lake. The average forecast from 31 points was 102% of the 1971-2000 average.

Conditions across the Bear River Basin held steady in terms of seasonal precipitation and snow compared to the other basins, as most weather systems during March focused their moisture on the Northwest and just skimmed the northern egde of Utah. Monthly precipitation was below average at 80% and seasonal precipitation dropped 3% to 97% of average. Snow water equivalent held mostly steady at 102% due to cool temperatures. Volumetric forecasts dropped 10% on the low end and 5% at the high end, now ranging from 58% of average near Montpelier to 106% at the Utah/Wyoming border.

The Weber and Ogden River basins had a much below average month for both snow accumulation and precipitation in March. Monthly precipitation was recorded at 65% of average and season precipitation dropped 6% and now totals 105% of average. Snow water equivalent numbers decreased from 114% of average to 108% of average at months end. Overall the April through July volumetric forecasts decreased slightly and range from 100% to 106% of average. At the top end this is a 10% decrease over the March 1st forecasts.

The Six Creeks basin experienced the same conditions as the Weber and Ogden basins experiencing cool temperatures for the month with much below average precipition. Monthly precipitation was much below average at 65% and seasonal precipitation dropped from 121% of average to 109% of average. Indexed snow numbers for the basin dropped from 131% of average to 124% of average. This still represents above average snow conditions and largest snowpack as a percent of average in the Northern Great Basin basin. April through July volume forecasts range from 105% to 114% of average, which represent about a 7% decrease in April through July volumes.

The Utah Lake Basin was the driest of all 4 basins during March yet enters April with an above average snowpack and average seasonal precipitation numbers. Monthly precipitation was much below average at 58% and seasonal values dropped 11% to 106% of average. Currently the indexed snow for the Utah Lake Basin is 111% of average. This snow pack value is on the cusp of normal to above average. April through July water supply forecast decreased by an average 7% and now range from 103% to 105% of average.

Differences between the full period forecasts and the residual forecasts may not exactly equal the actual observed volumes due to rounding conventions (see Definitions section).

10% exceedance forecast: Given the current hydrometeorological conditions, i.e current snowpack, soil moisture and streamflow, the volume that has a 10% chance of being exceeded. Previously referred to as "Reasonable Maximum Forecast".

50% exceedance forecast: Given the current hydrometeorological conditions, i.e current snowpack, soil moisture and streamflow, the volume that has a 50% chance of being exceeded. Previously referred to as "Most Probable Forecast".

90% exceedance forecast: Given the current hydrometeorological conditions, i.e current snowpack, soil moisture and streamflow, the volume that has a 90% chance of being exceeded. Previously referred to as "Reasonable Minimum Forecast".

Acre-Foot (af): The volume equal to one acre covered one foot deep (43,560 cubic feet). See kaf below.

Average: The arithmetic mean. The sum of the values divided by the number of values. Values from 1971-2000 are used for this publication.

Categories: Much Above Average=Greater than 130%, Above Average=111-130%, Near Average=90-110%, Below Average=70-89%, Much Below Average=Less than 70%.

CBRFC: Colorado Basin River Forecast Center.

Forecast Period: The period from April 1 through July 31, unless otherwise noted.

kaf: Thousand Acre-Feet. See Acre-Foot above.

Inflow: The volume of water that flows into a reservoir or lake.

Median: The middle value of an ordered set of values. Half of the values are higher and half of the values are lower. When the set contains an even number of values the median is the average of the two middle numbers.

NOAA: National Oceanic and Atomospheric Administration.

NWS: National Weather Service.

Water supply forecasts take into consideration present hydrometeorological conditions and use average basin temperatures and precipitation for the forecast period. As the forecast season progresses, a greater portion of the future hydrologic and climatic uncertainty becomes known and monthly forecasts become more accurate. For more information on the tools we use, consult Water Supply Forecasting Tools.

Volume forecasts represent adjusted flows; that is, observed flows with upstream water use taken into account. Adjusted flows will closely approximate natural or unimpaired flows. However, not all upstream diversions or impoundments are measured or quantifiable. For specific adjustments used with each forecast point, consult the Guide to Water Supply Forecasting.

The Water Supply Outlook is issued monthly January through May by the Colorado Basin River Forecast Center. It represents a coordinated effort between the National Weather Service, Natural Resources Conservation Service, Bureau of Reclamation, U.S. Geological Survey and local water district managers.

Note: Data used in this report are provisional and are subject to revision.

For more information, or to be included on the mailing list, please contact:

Colorado Basin River Forecast Center
2242 W North Temple
Salt Lake City, UT 84116
(801) 524-5130
www.cbrfc.noaa.gov