May 13, 2016
5
CapitalPress.com
Water
April heat produces dramatic PNW snowmelt
Capital Press
An April heatwave pro-
duced dramatic melting of the
mountain snowpacks in Ida-
ho, Oregon and Washington,
quickly fi lling reservoirs but
leading to worries in some ar-
eas that late-season water could
be scarce.
Idaho
Parts of Idaho lost a record
amount of mountain snowpack
during April, according to hy-
drologists at the USDA Natural
Resources Conservation Ser-
vice.
As a result, peak stream-
fl ows are occurring two to three
weeks ahead of normal, and the
streamfl ow forecast has shrunk
to 70 to 90 percent of average
throughout most of the state,
NRCS hydrologist Phil Mor-
risey said.
Morrisey said the snowpack
now ranges from 55 to 85 per-
cent of normal throughout the
state, with the greatest snow-
pack losses occurring from
Treasure Valley north through
the Panhandle.
He said the declines were
the result of dry weather and
high temperatures, which av-
eraged 3 to 10 degrees above
normal.
“This year we saw more
(April) decline in the snowpack
than in any of the other years
we’ve looked at it,” Morrisey
said.
Streamfl ow volumes for
April were more than 175 per-
cent of normal in the Bound-
ary, Bruneau, Deadwood, Big
Wood, Big Lost, Snake near
Moran and Willow Creek
drainages, as well as parts of
the Salmon and Boise drainag-
es.
The headwaters of the Snake
River at the Wyoming border
received just one-third of usual
April precipitation, and most of
the state’s basins received 40 to
60 percent of their usual mois-
ture for the month.
Southern Idaho was the ex-
ception to the dry month, with
April precipitation at 112 per-
cent of normal in the Owyhee
Basin, more than 150 percent
of normal in the Bruneau, Jar-
bidge and Salmon Falls basins
and 130-140 percent of normal
in the Oakley and Raft River
basins.
Morrisey said based on cur-
rent natural-fl ow and storage
conditions, marginally ade-
quate supplies are anticipated
in the Big Lost, Little Lost and
Big Wood basins. Morrisey said
reservoirs have above-normal
fi ll throughout the state and are
capturing the runoff, which has
been aided in reaching streams
by ample soil moisture.
Lynn Harmon, general
manager of the Big Wood Ca-
nal Co., said his irrigators rely
mostly on storage water, and
the early melting has helped his
water outlook, given that peak
fl ows were fi lling reservoir
storage before irrigators with
senior natural-fl ow rights up-
stream started diverting.
April changed that.
“This year highlights not
only the importance of peak
snowpack quantity, but also the
importance of the rate, timing
and amount of snowmelt,” the
NRCS said in its Oregon report.
Normally, melting snow
feeds streams at a slower pace
that sustains the water supply
later into summer, the NRCS
said.
Spring rains will be come
more important factors than
usual, the agency said.
“If plentiful, it could help
delay irrigation demand and
increase reservoir storage, po-
tentially offsetting or buffering
the impacts of early snowmelt,”
the agency’s snow survey team
concluded.
Washington
April was a month of rapid
snowmelt in the Washington
Cascades giving irrigators
plenty of water, but it may not
last into late summer in valleys
with little or no reservoirs.
Pear orchards in some parts
of the Wentachee Valley, or-
chards to the north in the En-
tiat Valley and orchards and
hay fi elds even farther north
in the Methow and Okanogan
valleys may run low on water
in August and September.
Junior water right holders
in the Yakima Basin are fore-
cast at 85 percent of the nor-
mal supply by late summer, the
U.S. Bureau of Reclamation
announced May 5.
That shouldn’t affect irriga-
tors such as the Roza Irrigation
District and Kittitas Reclama-
tion District but means they
and other juniors will need to
be careful with water, a USBR
offi cial said.
“We’ve seen the fastest
melt rate we’ve ever seen —
record rates or second-fastest
rates in over 80 percent of our
SNOTEL (snowpack teleme-
try) sites with 15 years or more
of data,” said Scott Pattee, wa-
ter supply specialist with the
NRCS in Mount Vernon.
“Sites below 5,000 feet
have melted out two to three
weeks early and right now the
snow level is 5,000 to 5,500
feet,” Pattee said.
Statewide snowpack was
107 percent of normal on April
5 but had dropped to 73 percent
of normal by May 4, he said.
The best snowpack all winter
was in the upper Columbia, but
that’s now 68 percent versus
134 percent a month ago, he
said.
May 5 through September
streamfl ow forecasts are re-
fl ecting the earlier than desired
loss of snowpack, Pattee said.
Rapid snowmelt has caused
the highest unregulated fl ows in
the Yakima River at the USBR
station at Parker in the past 35
years and the second-highest
in the past 90 years, said Chris
Lynch, a USBR hydrologist in
Yakima.
The Wenatchee River and
other rivers draining the east
slopes of the Cascades have
been running full for a month.
The only thing that’s prevent-
ed fl ooding has been that there
was little to no rain, Pattee
said.
Precipitation at the fi ve wa-
ter reservoirs in the Yakima
Basin was 14 percent of aver-
age in April, which is a new
record, beating 15 percent for
that month set in the 1930s and
1950s, Lynch said.
“I don’t want to raise any
big alarms, but it’s a very inter-
esting statistic,” he said.
It means April was a dry
month, which by itself may not
mean much but would if March
had been dry, he said. May usu-
ally is drier than April. As of
May 3, the fi ve Yakima reser-
voirs were 94 percent full and
at 126.7 percent of the average
from 1981 through 2010.
“We hope to have them full
Western U.S. snow water equivalent
Basin-wide percent of 2016 snowpack compared to
the aggregate average (1971-2010).
72
80
37
40
71
75 49
67
68
57
41
52
74
59
41
6
2
46 46
67
41 38
56
47
27
61 43
77
56
47
62 62 57
62
10
65
50
54 63
71
53 45 64
62
68
61
34
55
78
55
76
35
66
68
36
23 65
35 123107
141
35 107 66 141 75
77
70
126 168
141
72 88
95
118 138
121
68
101
106
72 202 150
121
73
109
64 93
138
116 120
110
160
118
110
48
119131
5
105
177
156 1850 104
120
Percentage key
(As of May 9)
74
0
Unavailable
Less than 50%
50-69%
70-89%
90-109%
110-129%
130-149%
More than 149%
Miles
0
Source: USDA, Natural Resources Conservation Service
by mid to late May and be able
to make it into June before we
150
300
Capital Press graphic
start drawdowns for irrigation,”
Lynch said.
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Oregon
April’s heatwave was so in-
tense that nine automated snow
monitoring sites in Oregon re-
corded the most dramatic April
snowmelt on record.
Among monitoring sites that
typically have snow on May 1,
75 percent lost between 3 and
4 feet of snow in the month,
according to the USDA’s Nat-
ural Resources Conservation
Service.
The early runoff helped
fi ll reservoirs around the state,
but means streamfl ows will be
below normal this spring and
summer, especially in Southern
and southeastern Oregon, the
NRCS reported in its May wa-
ter supply bulletin.
“Once the snow is gone,
streams will be at the whim
of temperatures and spring
rainfall,” the NRCS Portland
snow survey team reported.
The National Oceanic and At-
mospheric Administration’s
Climate Prediction Center said
the state can expect above nor-
mal temperatures for the next
three months, although with
above normal rain in Southern
Oregon.
Much of the Pacifi c North-
west received normal to above
average rain or snow last fall
and winter, and by the end
of March the snowpack was
above average in many areas.
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