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Snow Survey Bulletin
Snowpack and Water Supply Outlook for British
Columbia
April 1, 2005
Every
effort is made to ensure that data reported on these
pages are accurate. However, in order to update the graphs
and indices as quickly as possible, some data may have
been estimated. Please note that data provided on these
pages are preliminary and subject to revision on review.
The April 1st snow survey is now complete.
Data from 165 snow courses and 60 snow pillows around the
province, with 27 out of province sampling locations and climate
data from Environment Canada, have been used to form the basis
for the following reports.
Snowpack
Snow conditions are quite variable
across the province for April 1st, with much of southern BC
having below normal snowpacks, and central and northern BC
having near ormal or above normal snowpacks. Precipitation
during the last half of March resulted in snow water conditions
in most areas remaining close to their March 1st percentage
of normal levels. For Vancouver Island, the lower Fraser valley
and the South Coast, however, late-March precipitation has
resulted in significant increases in snow water. Never-the-less,
these areas, along with the Similkameen, portions of the west
and south Okanagan, and southern portions of the East and
West Kootenay continue with well to far below normal snowpacks.
For Vancouver Island and the Similkameen, the current snow
water conditions remain a record low. Southern portions
of the Middle Fraser also have less snow than usual. The North
Thompson, South Thompson, Upper Fraser, Skeena, Peace and
Liard river basins have snowpacks ranging from near normal
to slightly above normal.
A notable condition for April 1st is the virtual
absence of low elevation snow throughout much of south and
central BC. Most low elevation snow throughout the Fraser,
Thompson, Okanagan, Kettle and Similkameen basins, along with
the Kootenays and the south coast, melted off in mid-January
during a prolonged intense Pacific frontal storm system. Our
Fraser basin "Low Elevation Index" is currently
only 21% of normal snow water.
Weather
Precipitation during March was normal
to above normal in most areas of the province, except the
upper Fraser, portions of the Columbia, and the Stikine. Overall,
precipitation over the last five months (Nov-Mar) has been
normal or above normal for most of BC. Exceptions are Cranbrook
in the Kootenays and Princeton in the Similkameen, with Nov-Mar
precipitation of only 68% and 75% of normal, respectively.
Temperatures during March were above normal throughout much
of BC, particularly for the first half of the month. Since
mid-March temperatures have moderated closer to seasonal norms.
The high temperatures in early March contributed to continuing
low elevation snow melt in some areas, and further ripening
of the snowpack throughout central and southern BC.
Runoff from rivers throughout the province
remained high during March, for the fourth consecutive month.
The Fraser River near Marguerite, the Fraser River at Hope,
the Similkameen River at Princeton, and the Kootenay River
at Fort Steele all continued with well above normal runoff,
based on preliminary WSC data.
Outlook
By April 1st, on average, greater
than 95% of the peak snowpack for the year has accumulated,
with the peak snowpack occurring generally around mid-April.
Some regions have very low snowpack and little season remaining
to accumulate additional snow. These include the South Coast,
Vancouver Island, Lower Fraser, Similkameen, the south and
west Okanagan, and the southern Kootenays.
For these regions we are anticipating an earlier
than usual onset of low flow conditions. Unless significant
snow accumulations occur over the remaining winter period
and spring precipitation is at least normal, there is potential
for unusually low summer season flow in rivers throughout
southern BC, and throughout the south coast and Vancouver
Island. This is particularly so for rivers unsupported
by storage.
Some regions currently have near enough normal
snowpacks that peak snowpacks for the year are anticipated
to be near normal or even above normal. These include the
Peace, Nechako, Stikine, Liard, Skeena, Upper Fraser, North
Thompson and South Thompson. For these areas there is a significant
potential for high flows during May and June, during the snowmelt
freshet runoff.
April 1
The Snow Water Index for the upper Fraser is at 100% of normal
for April 1, similar to its April 1st level.
Precipitation at Prince George was below normal for March
(66% of normal), but was 90% of normal for November-March.
Low elevation snow is well below normal.
The Nechako Snow Water
Index is 95% of normal. Mid and upper elevation snowpacks
appear near normal, while lower elevation snow is below normal.
Precipitation in the Nechako basin was above normal during
March.
Regional streamflows were well above normal
during March. Runoff from the Fraser River at Marguerite,
a regional indicator, was 206% of average for the month.
April 1
Snow water equivalencies throughout the middle and lower Fraser
are highly variable as of April 1. The Middle Fraser overall
had an overall April 1 Snow Water Index of 75% of normal,
an increase from the March 1 value. Southern portions of the
middle Fraser have snow water equivalencies in the 30-60%
range. In addition, low elevation snow is very low, and absent
in many areas. The Fraser River "Low Elevation Index"
was at 21% of normal for April 1.
The Lower Fraser had well below normal snowpacks
as of April 1, with a Snow Water Index of only 43% of normal.
A number of snow courses are reporting record low snow
water for this date. The extremely low snowpack levels throughout
the lower Fraser result, in part, from the significant melt
and runoff experienced during mid-January, when an intense
Pacific frontal system moved onto the south coast, producing
high rainfall and elevated freezing levels. Some snowmelt
and snowpack ripening has continued with the warm temperatures
during the first half of March.
Streamflows remain well above normal for this
date, reflecting the rainfall and warm temperatures over the
past 3 months. The Fraser River at Hope, used as a regional
indicator, experienced 171% of normal runoff for March.
April 1
The North Thompson Snow Water Index is 92% of normal for April
1, which is a decrease from March 1. Precipitation in the
basin was close to normal for March (97% of normal for Blue
River), but above normal for the cumulative winter period
(112% of normal for November - March). Snow pack development
appears to be good at mid and high elevations, but with below
normal snow at low elevation. The Blue River and Knouff Lake
snow courses both lost snow water between March 1 and April
1.
The South Thompson Index was
90% of normal at April 1, similar to its March 1 value. Snowpack
development appears to be close to normal at high elevation,
but is poorer at low elevation. Some low elevation snow melted
off during the January 17-22 period, from the combination
of rain and prolonged warm temperatures associated with a
Pacific frontal system.
Streamflows in the region, as indicated by
the mean monthly flows in the Thompson River at Spences Bridge,
have remained above normal since November, due to the warmer
temperatures and rainfall. The March average discharge was
177% of normal.
April 1
The mid to upper elevation Snow Water Index for the Upper
and Lower Columbia is at 86% of normal, decreased from the
March 1 value of 89%. Individual snow survey stations range
from well below to slightly above normal. Precipitation at
Revelstoke was 59% of normal for March, and 85% of normal
for the cumulative November - March period.
Streamflows in the region, as represented
by the mean monthly flow in the Columbia River at Donald,
were above normal March, at 120% of normal.
April 1
The April 1 Snow Water Index
for the Kootenay is only 76% of normal, unchanged from its
March 1 value. Individual station readings are variable. For
the East Kootenay, low elevation snow appears to be well below
normal, while high elevation snow is 70-90% of normal. Many
stations in the West Kootenay are well below normal for April
1, in the 50-70% of normal range.
Cranbrook, the Kootenay indicator
climate station, has had comparatively
less precipitation than any other indicator station in the
province. It received well above average precipitation during
March, but is still only at 68% of normal for the November
to March period.
Streamflows, as indicated by the mean monthly
flows in the Kootenay River at Fort Steele, have continued
for the fifth consecutive month of being above normal. The
March average runoff was 130% of normal.
April 1
The overall Snow Water Index for the Okanagan-Kettle is 82%
of normal, largely unchanged from March 1. Individual station
readings for the Kettle are generally below 85% of normal.
For the Okanagan, individual station readings vary from below
to well below normal. Only one station is above normal at
April 1 (Mission Creek snow pillow, at 119%). In
general, snow water values at low elevation and along south
and west sides of the Okanagan are low, in the 45-75% of normal
range. Snow water values at higher elevation and along the
north and east side of the Okanagan basin are higher. Silver
Star Mountain is 89% of normal, Greyback Reservoir is 85%,
and Graystoke Lake is 86%. Trout Creek on the west valley
is only 58% of normal.
The Similkameen basin Snow Water Index is
only 44% of normal for April 1. This is the lowest April
1 index value recorded for the Similkameen. Based on an
April-July volume runoff forecast of 740 million cubic metres
(602,000 acre-feet) (45% of 1971-200 Normal) for the Similkameen
River at Nighthawk, the International Osoyoos Lake Board of
Control will likely issue a formal drought declaration with
respect to the operation of the Zosel Dam on Osoyoos Lake
near Oroville, Washington.
Precipitation at Kelowna was
slightly above normal for March, and for the Nov-Mar cumulative
winter period (107% of normal). Precipitation at Princeton,
in the Similkameen, was 110% of normal for March but only
75% of normal for the 5-month period of November - March.
An additional factor the the low snow in the Similkameen and
south Okanagan is the intense Pacific frontal system that
affected south and central BC during the January 17-22 period.
The elevated freezing levels and rainfall associated with
this event resulted in significant snowmelt and runoff.
Streamflows in the region, as indicated by
inflows to Okanagan Lake, were far above normal during November,
December, January and March, due to fall and winter rainfall,
and warmer than usual temperatures producing snowmelt. Inflows
during March were 57.7 kdam^3 (237% of normal), while inflows
during the 5-month November - March period were 181 kdam^3
(272% of normal).
April 1
Snow packs on the Vancouver Island and South Coastal regions
remain well below normal as of April 1. The Vancouver Island
average snow water index is only 21% of normal. This is a
record low for April 1. The South Coastal index is 43% of
normal, close to a record low. Despite their low levels, significant
increases in snow water on Vancouver Island and the South
Coast have occurred since mid-March.
Precipitation on Vancouver
Island and the Coast was near normal for March, and near normal
for the cumulative November to March period (90% at Nanaimo,
110% at Vancouver). However, much of the precipitation has
occurred as rain, and substantial portions of the early winter
accumulated snowpack melted off and became runoff during the
mid-January "Tropical Punch" event. The Jump Creek,
Wolf River, Upper Squamish, Chilliwack River, Wahleach, Great
Bear, Spuzzum and Nostetuko snow pillows are all below record
lows for April 1.
Despite their
low levels, significant increases in snow water on Vancouver
Island and the South Coast have occurred since mid-March.
The Jump Creek pillow went from 0 mm snow water
equivalence on March 18 to 185 mm on April 1 (and to 305 mm
on April 7).
Stream flows, as indicated by mean monthly inflows to Upper
Campbell Lake, were below normal during February and March,
after being well above normal during November, December and
January.
April 1
Precipitation in the Peace River basin was above normal for
March (134%), and has been normal for the cumulative November
- March period (97% at Ft. St. John). Overall, snow water
conditions in the Peace River basin are good. The snow water
equivalencies range generally from 90% to 120% of normal,
with a basin average of 107% of normal, a significant increase
from March 1.
Precipitation in the Liard River basin has
been variable, with above normal precipitation for March,
but close to normal precip for November - March. The basin
Snow Water Index is 105% of normal at April 1, unchanged from
March 1. Individual station values are quite variable, with
snow water equivalencies range between 60% and 170%. Mid and
high elevation snow in the Liard appears to be well above
normal.
Regional stream flows, as reflected by the mean monthly inflows
to Williston Lake, have been well above normal for March,
continuing a pattern since November.
April 1
The Skeena/Nass basins have an average snow water index of
102% of normal for April 1, increased from their March 1 values.
The Stikine/Taku basins have an average index of 99% of normal,
reduced from March 1. There is some variability with the distribution
of snow across the Northwest, with coastal areas appearing
to have below normal snow packs while inland areas have normal
to well above normal snow packs.
Precipitation across the Northwest
has been variable during the winter. Precipitation at Smithers
was 156% of normal for March, and 122% of normal for the cumulative
November - March period. November was very wet (172%), associated
with two Pacific frontal storms. For Dease Lake (Stikine index
station), March was dry at only 46% of normal. The Stikine
has received above normal precipitation over the winter (114%
for November - March).
Regional stream flows, as reflected by the mean monthly flows
in the Skeena River at Usk, remain well above normal. Monthly
runoff was 135% of normal for November, 164% for December
and 146% for January, 158% for February and 224% for March.
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