Ministry of FLNRO

Snow Survey and Water Supply Bulletin - March 1st, 2017

The March 1st snow survey is now complete. Data from 154 snow courses and 72 automated snow weather stations around the province, collected by the Ministry of Environment Snow Survey Program and partners, and climate data from Environment and Climate Change Canada have been used to form the basis of the following report.

Click here for the Snow Survey and Water Supply Bulletin as a PDF file.
Click here for the complete March 1, 2017 Snow Survey Data.
Click here for the Basin Snow Water Index Map.

Weather
February was dominated by persistent high pressure over British Columbia and offshore which generally brought stable, dry, cold weather conditions across the province. This pattern of stable weather was interrupted at times with periods of instability which brought light to moderate precipitation, including snowfall at low elevations. A strong atmospheric river event in the middle of February brought heavy rain and seasonally warm temperatures to south-west BC, leading to the melt of low elevation snow.

For the month of February, temperatures were 1 to 4˚C below-normal through most of BC, except in the north, where temperatures were slightly above-normal. Overall precipitation patterns for February were mixed across the province, with drier conditions in the north coast and west-central areas of BC, wetter conditions in the South Coast, South Interior and Kootenay, and near normal precipitation elsewhere in the province.

Weather across the entire winter period (December, January and February) tells a similar story, with persistent colder than normal temperatures (1-3˚C) over the southern half of BC, and warmer than normal temperatures over the north. Dry conditions have been prevalent over most of the province this winter.

Snowpack
Weather patterns through February led to modest shifts in snow pack conditions across the province. In the South Interior and south-east BC, snow basin indices saw increases in values from February 1st. Declining snow basin indices occurred in coastal and northern BC, while indices in central locations were generally stable from February 1st values. The provincial average for all March 1st snow measurements is 85% of normal, which is an increase from the average of 79% in February.

Snow basin indices for March 1st 2017 range from a low of 45% of normal in the Liard to a high of 99% in the East Kootenay (Table 1 and Figure 1). Below normal snowpack (65-80%) is present in the Upper Fraser, Vancouver Island, Skeena-Nass and Northwest, and well below normal (<65%) in the Boundary, Stikine, Liard and Peace. Near-normal snowpack (80-100%) are present throughout the rest of the province. The March basin index for the entire Fraser River basin is at 83%, which is approximately a 1-in-15 year low snowpack or the 10th lowest March index in the past 65 years.

With cooler than normal temperatures through this winter, low elevation areas have been cold enough that they have experienced a greater proportion of precipitation as snow than normal. For example, most Environment and Climate Change Canada weather stations that record snow observed 2 to 8 times the normal snowfall amounts in February. This season’s snowpack can be considered “upside-down”, with higher than normal snowfall occurring at low elevations, but below-normal snow at high elevations. This is a result of colder than normal temperatures which have resulted in several low elevation precipitation events occurring as snow rather than rain. However, seasonally dry conditions have resulted in lower than normal snowpack at high elevations despite the colder conditions. Increased snow at low elevations plays a limited role in seasonal flood risk or water supply into the spring and summer.

Table 1 - BC Snow Basin Indices – March 1, 2017


Basin

% of Normal

Basin

% of Normal

Upper Fraser West

66

Boundary

59

Upper Fraser East

66

Similkameen

83

Nechako

95

South Coast

90

Middle Fraser

84

Vancouver Island

72

Lower Fraser

95

Central Coast

84

North Thompson

87

Skagit

98

South Thompson

87

Peace

64

Fraser River – Entire

83

Nicola

83

Upper Columbia

87

Skeena-Nass

74

West Kootenay

91

Stikine

52

East Kootenay

99

Liard

45

Okanagan

86

Northwest

77

Outlook
La Niña conditions in the equatorial Pacific Ocean have ended, with the Climate Prediction Centre (CPC) at the U.S. National Weather Service/NOAA ending the La Niña Advisory in early February 2017. Neutral ENSO conditions are now present, and the CPC is forecasting an increased likelihood of neutral conditions persisting through the spring of 2017, with the potential for El Niño conditions into the summer-fall period. Negative sea surface temperature anomalies are present in the North Pacific Ocean west of British Columbia. Seasonal forecasts from Environment and Climate Change Canada reflect current ocean temperature conditions, with an increased likelihood of normal temperatures over the March-May period for most of the province, and below-normal temperatures over coastal BC and north into the Yukon.

Seasonal volume runoff forecasts (see below) are near normal for most basins across the province with below-normal seasonal runoff forecasted for the Kalamalka-Wood basin.

By early March, 80% of the annual BC snowpack has typically accumulated. At this stage in the season there is limited indication that any region of the province is developing increased seasonal flood risk due to high snowpack. While snowpack is an important factor in seasonal flooding, weather during the melt season, particularly extreme rainfall events, can also create flood risk even in years with low snowpack.

Well-below normal snowpack in the Stikine, Liard, Peace and Boundary, and below normal snowpack in the Upper Fraser, Skeena-Nass, Vancouver Island, and the Northwest indicate the potential for increased risk of low flows this summer. Summer weather is also an important factor in summer low flows, particularly on Vancouver Island and northeast BC, and wet or dry weather through the summer period can affect the risk of low streamflow.

With six to eight weeks remaining in the snow accumulation season, changes to the seasonal runoff outlook are possible, but at this stage would require extremely wet or cool conditions to make a significant impact on seasonal flood risk.

The River Forecast Centre will continue to monitor snowpack conditions and will provide an updated seasonal flood risk forecast in the April 1st 2017 bulletin, which is scheduled for release on April 6th.

BC River Forecast Centre
March 7, 2017