WSP04526

• File Number: 8210.137
• Description: Colorado River Basin-Colorado River Basin Organizations/Entities-Colorado River Forecast Committee
• Date: 5/1/1992
• Author: USDA, USDC, NOAA,NWS
• Title: Water Supply Outlook for the Western United States
• Water Supply Pro - Doc Type: Report/Study

UUl'/il(i

1992 Snowmelt Season
as of May 1

Unusually warm temperatures during April only served to exacerbate an
already grim water supply outlook ror the West. As a result, below average
snowpacks were severely depleted and the melt season started considerably
earlier Ihan usual. Below to well below average streamnows are expected ror all
the weslern states, except New Mexico and parts or Utah, Colorado, Arizona.
British Columbia, and Alaska.

General Outlook

Spring runoff began somewhat earlier
than usual this year us April tempera-
tures melted the already deficient
snowpacks found in most of the western
states. May 1 forecasts indicate that
almost the entire West will be faced
with below to well below :lverage
streamtlows. Only the southernmost and
northernmost areas of the West are
slated to receive average or above aver-
age streamilows.
Streamflow. Forecusts for spring and
summer stream flows remain bleak.
Most of the West can expect stream~
flows below 70 percent of average.
Near record low volumes are expected
in the northem portion of the Great
Basin. the southern portion of the Co-
lumbia River Basin. and the Green
River tributaries of the Colorado River

Bnsin. The only areas expected to pro-
duce near average to well above
average runoff are in New Mexico,
southern Colorado. the southeastern
comer of Utah, the northern portion of
the Col umbia River Ba"iin in British Co-
lumbia, and southeastern Alaska.
Precipitation during April followed
the same pattern exhibited in previous
months as most of the moisture was
again routed to the north and the south
leaving the middle portion of the West
"high and dry"', Precipitation totals ill
the Great Basin. Arkansas River Bj)sin.
Colorado River B<Jsin. the southern
ponion of the Missouri River Basin, and
the westenl h<Jlf of Alaska were below
to well below average, The northern
portions of the Columbia River Basin
and the Missouri River Basin, the south-
ern portions of California. Arizona, and
New Mexico. and the eastern half of
Alaska reported precipitation totals that
were near 1O well ahnve aventge.

Streamflow. With the exception of a
few isolmed areas in the southern por-
tion of the western United Stiltes and
the central and southeastern portion of
Alaska. snow packs throughout the west-
ern states are below to well below
average. Low to mid-elevation SIlOW-
packs are all but non-existent in most
areas and the higher elevation snow is
considerably less than would nonllally
be found there at this time of year.
Reservoir storage on the last day of
April was below i1verage for most of the
western stiJtes. At \4 percent. Nevada
continues to have the lowest statewide
percent of average stomge. Not surpris-
ingly. the southern states (ArizoniJ. New
Mexico, Colorado) and Washington are
the only states reponing above iJverage
storage.

Basin by Basin

Summary

Alaska
April proved to be a dry month for most
of Alaska. Notable exceptions if1(,:luded
the Copper and Tanana river basins.
where precipitation totals were three to
four times the monthly average.
Below average temperatures in the
interior during April delayed the onset
of the spring ice break-up in the north-
ern half of the state. In the south. rela-
tively W,Ulll temperatures combined
with the moisture shortfall to eliminate
most low elevation snowpacks. Howev-
er. very heavy mounwin snowpacks
persisted over ponions of the Kenai
Peninsula. northern Cook Inlet, and the
Copper and Tanana basins.

Missouri Basin
Precipitation. April precipit<Jtion in the
Missouri Basin wus highly variable,
ranging from 5 percent of iJverage at
Casper. Wyoming. to 333 percent of
average at Harlowtoll, Montana. April

precipitation was generally below aver-
age in northeast Colorado, Illost of Wy-
oming, and north-central Montana. The
remainder of Montana and northwest
Wyoming tended to have average to
much above average precipitation.
SlIowpack. The high elevation snow-
pack in the Missouri Basin is much
below average for this time of year.
May I snow pack for the Missouri main-
stem above Fort Peck, Montana, is about
60 percent of average. which is also the
average for the Yellowstone Basin.
Mountain snowpiJck in the North Platte
Basin is about 45 percent of average.
Streamflow. Most streams in the Mis-
souri Basin are forecast to have below
to much below average runoff this spring
and summer. Strei.imflow forecasts for
the Missouri Basin above Fort Peck
range from 30 to 80 percent of average.
Runoff in the Yellowstone Basin is
expected to be about 65 percent of aver-
age. Flows in the North Platte Basin are
predicted to average around 30 perl'eot,
whereas the South Platte is forecast to
have ubout 80 percent of average.

Reservoir storages in Montana are
generally near average for this time of
year except for Lima. Clark Canyon.
Lake Sherburne ,md Fort Peck. where
stored water is below average. In Wyo-
ming reservoir storages are average in
the Big Horn Basin but generally below
average elsewhere. Stored water in the
South Plane Basin is near average.

Arkansas Basin
The Arkctllsas River Basin water supply
outlook indicates below avemge amounts
of runoff in the mainstem of Lhe Arkan-
sas Rivcr and above average amounts
for its tributaries. Volume totals are
predicted to be 65 to 79 percent of aver-
age along the mainstem and 90 to 120
percent uf ;.werage along the tributaries.
Precipitation. Monthly precipitation
totals were generally below nonnal
along the mainstern with values jJVerag-
ing about 46 perceIH of nornlal. The
tributary basins did somewhat worse
with viJlues averaging near 25 percent
of nornlal. The range extendcd from a
low of 14 percent near Buena Visla to
153 percenl of nonnal near Fountain.