IntermtnClimateSummaryJan2008

• Title: Intermountain West Climate Summary
• Date: 1/22/2008
• Description: Water Availability Task Force Meeting Report
• Basin: Statewide
• Drought Mitigation - Doc Type: Reports

INTERMOUNTAIN WEST CLIMATE SUMMARY, JANUARY 2008

Utah Water Availability

Snowpack is the primary determinant of water supply estimates
from December-April 1. Statewide snowpack ranges from a low of
40-79% of average in the Weber, Ogden, and Uintah basins in the
north to a high of 120-> 160% of average in the Virgin and Beaver
River basins in the south (Figure 9a). Historically, below average
snowfall in southern basins and near or above average snowfall in
northern basins is associated with La Nina conditions. While La
Nina conditions persist in the equatorial Pacific, the snowfall pat-
terns in Utah are uncharacteristic of past La Nina years, according
to the NRCS.
Reservoir storage statewide is 15 percentage points below
storage this time last year due to below average snowfall and
streamflows during WY2007. Reservoir storage is lowest in the
Bear River basin at 20% of average and highest in the Provo and
Duchesne basin at 78% of average. Initial April-July streamflow
forecasts released by the NWS project a low of 51 % of average on
Bear River to a high of 122% of average on the San Juan River.
April-July inflow projections into Lake Powell are 101 % of aver-
age. For additional information on spring and summer streamflow
forecasts, see page 17.
SWSI values are near or below average statewide, ranging
from a low of -3.49 in the Bear River basin to a high of 2.17 in the
Virgin River basin (Figure 9b). Although the majority of the snow
accumulation season still lies ahead, above average snowpack is
needed to improve drought conditions statewide. For information
about Utah's drought status and expected persistence, see page 7
for the U.S. Drought Monitor and page 15 for the U.S. Drought
Outlook.

Notes
Figure 9a shows the SWE as a percent of normal (average)
for SNOTEL sites in Utah, courtesy NRCS. According to the UT
NRCS, "The Surface Water Supply Index (SWSI - Figure 9b) is a
predictive indicator of total surface water availability within a wa-
tershed for the spring and summer water use seasons. The index
is calculated by combining pre-runoff reservoir storage (carryover)
with forecasts of spring and summer streamflow, which are based
on current Snowpack and other hydrologic variables. SWSI values
are scaled from +4.1 (abundant supply) to -4.1 (extremely dry) with
a value of zero (0) indicating median water supply as compared
to historical analysis. SWSl's are calculated in this fashion to be
consistent with other hydroclimatic indicators such as the Palmer
Drought Index and the [Standardized] Precipitation Index." See
page 9 for the SPI.

w;f--

Current. Snow
Water Equiv.
0/0 of INormal
A .> 160ft;)
.... 140- u60'--):i
~ 120.139'%
... '100.119%
r;; E10-89%
~ 61).79%
... 40-59%

-:;!fI
V'
V

.~

.A

y 1-'38%

'J.l
;
Lz.:;

+ 0%

. IJn8\l"ailable'"

Figure 9a. Current snow water equivalent (SWE) as
a percent of normal for SNOTEL sites in Utah as of
January 2, 2008 (NRCS).

+4.1 Abundant Supply
o Median Water Supply
-4.1 Extremely Dry

Virgin
2.17

Figure 9b. Utah Surface Water Supply Index as of
January 1, 2008 (Utah NRCS).

On the Web
· For current maps of SWE as a percent of normal as shown in Figure 9a, go to http://wcc.nrcs.usda.gov/gis/.
· The Utah SWSI, along with more data about current water supply status for the state, can be found at: http://www.ut.nrcs.
usda. gov Isnow/watersupply I.
· The Palmer Drought Index is found on NOAA's drought page: www.drought.noaa.gov.
· The Utah January Water Supply Outlook is available by state and basin at: http://www.ut.nrcs.usda.gov/snow/watersup-
I Iwsor.html.

RECENT CONDITIONS 112