**Modeled Snow Cover Product (Snow Water Equivalent)**\
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Posted snow water equivalent (SWE) graphs are the product of a spatially
distributed snowmelt model forced with a remotely sensed and assimilated
meteorological data as weather data input. The model is based upon the
Utah Energy Balance (UEB) snowmelt model developed by Tarboton
(Tarboton, 1994; Tarboton et al., 1995). The UEB model is very
parsimonious with only three state variables. The model uses a lumped
representation of the snowpack with two primary state variables, namely,
water equivalence (or total amount of water, expressed in depth, in the
snowpack), and energy content relative to a reference state of water in
the ice phase at 0 ^o^C. This version of the model runs in a spatially
distributed mode using a grid resolution of 10 km.\
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The energy content is used to determine average snowpack temperature,
and/or fraction of the snowpack that is in liquid form. Age of the snow
surface is retained as a third state variable, used for the calculation
of albedo (or reflectance properties of the surface). The model is
driven by inputs of air temperature, precipitation, wind speed,
humidity, and radiation at a 6-hourly time step, a time step that is
sufficient to resolve the diurnal cycle. The model uses physically-based
calculations of the radiative, sensible, latent and advective heat
exchanges (i.e., exchanges, or fluxes, of energy due to incoming and
outgoing short- and long-wave radiation, thermal or heat conduction,
evaporation and condensation, and horizontal heat transport). An
equilibrium parameterization of snow surface temperature accounts for
differences between snow surface temperature and average snowpack
temperature, without having to introduce additional state variables.
Melt outflow is a function of the liquid fraction, and is parameterized
according to Darcy\'s law; this parameterization allows the model to
account for continued outflow even when the energy balance is negative.\
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The daily rainfall input grids are the [[satellite rainfall estimates
(RFE)]{.underline}](http://igskmncnwb015.cr.usgs.gov/adds/readme.php?symbol=rf)
provided by NOAA/CPC (Climate Prediction Center) (Xie et al., 1997). The
RFE is calculated on a 0.1-degree latitude/longitude grid. The remaining
input variables required by the model (solar radiation, air temperature,
wind, humidity, and atmospheric pressure) are estimated from downscaled
output fields from NOAA\'s Global Data Assimilation System (GDAS) and
the Air Force Weather Agency\'s MM5 (Mesoscale Model, version 5) weather
forecast model.\
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The (daily) snow water equivalent maps show the spatial distribution of
the modeled water content of the snowpack. As such, the maps also
portray the spatial distribution of snow cover extent, and provide an
indication of relative snow depth and water available for irrigation
when the snow melts.\
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Three years means were calculated for each day of the year based on data
from the years 2005 to 2008. Anomaly maps are produced to display the
absolute difference from the mean and the percent difference from the
mean for each day.\
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Tarboton, D. G., T. G. Chowdhury and T. H. Jackson, (1995), \"A
Spatially Distributed Energy Balance Snowmelt Model\", in
Biogeochemistry of Seasonally Snow-Covered Catchments, ed. K. A.
Tonnessen et al., Proceedings of a Boulder Symposium, July 3-14, IAHS
Publ. no. 228, p.141-155.\
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Tarboton, D. G., (1994), \"Measurement and Modeling of Snow Energy
Balance and Sublimation From Snow\", in Proceedings, International Snow
Science Workshop, Snowbird, Utah, October 31 to November 2, Utah Water
Research Laboratory working paper no. WP-94-HWR-DGT/002.\
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Xie, P. and P.A. Arkin, (1997), \"A 17-year monthly analysis based on
gauge observations, satellite estimates, and numerical model outputs\",
Bulletin of the American Meteorological Society 78(11): 2539-58.