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Snowpack Update April 23, 2015
2,500
Change in Snowpack 4/16 to 4/22
Snowpack Volume (Kaf)
2,000
1,500
1,000
Net year to year
change
(2,100) Kaf
Accumulation
2,100 Kaf
500
0
(500)
(1,000)
Total Reduction
to Snowpack
3,400 Kaf
Total Reduction
to Snowpack
3,400 Kaf
(1,500)
(2,000)
(2,500)
GCL
IHR
GCL
2014
Accumulation
300
Inflows (Kcfs)
250
IHR
2015
Melt
OBSERVED FLOWS AT THE DALLES
Upper Columbia Reservoir Draft
200
150
100
Upper Columbia Reservoirs
Pass Inflows
50
0
16-Apr
17-Apr 18-Apr 19-Apr
OBS_2014
Net_of_Reg_2014
20-Apr 21-Apr
OBS_2015
Net_of_Reg_2015
22-Apr
Columbia. Inflows at The Dalles over the period
averaged 142 Kcfs in 2015 and 237 Kcfs in 2014, a
difference of 95 Kcfs (Chart 2). A large part of this
year over year difference is attributed to storage
draft at Upper Columbia reservoirs; which in 2014
supplemented flows by an average of 75 Kcfs, but in
2015 did not contribute significantly to flows. The
importance of this is two-fold: 1) less reservoir draft
in April 2015 relative to April 2014 has resulted in
current storage levels that are nearly 7.8 Million
acre-feet above that of last year at this time, 2) with
reservoir levels higher this year May refill
requirements will be substantially less. Based on
changes in storage levels during May 2014, reservoir
refill reduced unregulated flows an average of 148
Kcfs. To meet the same end of May reservoir
elevations, based on current reservoir elevations
total refill required is less than 700 Kaf (9,100 Kaf of
refill occurred in May 2014). Although a number of
reservoir operational considerations may influence
actual end of May 2015 reservoir levels, it is
apparent from this analysis that large adjustments
natural May/June flows for reservoir refill are not in
the forecasts.
Forecasted Inflows (Kcfs)
Total snowpack declined by over 3,400 Kaf from
The STP forecast for the past few weeks has been
April 16 to April 22, which is very similar to the snow
consistently over-forecasting flows on the Lower
melt values for 2014; however, in 2014 at elevations
Columbia. Given a relatively consistent seasonal
above 4500 ft. snowpack increased by 2,100 Kaf
volume this over-forecasting of April flows has
above Grand Coulee (Chart 1). The NWRFC 10 day
forced the remaining seasonal volume into the
QPF forecasts significant precipitation over the next
balance of the forecast (Chart below).
several days focused
largely on coastal areas to
Observed and Forecasted Flows at The Dalles
250
the Cascades. The degree
to which this precipitation
reaches the interior of the
200
Columbia River basin may
make the difference
150
between a continuation of
Continued Over-forecasting
the recent declines to
100
seasonal runoff and a
Over-forecasting of April flows forces
pause in the trend.
The similar volume of
snowmelt year over year
for the week of April 16 to
22 was not reflected in
flows on the Lower
50
0
6-Apr
Shifting of volume to May
16-Apr
26-Apr
6-May
Apr-14_STP
.
16-May
OBS
26-May
STFQ
5-Jun
15-Jun
Apr-20_STP
25-Jun
5-Jul