Ministry of FLNRO

Snow Survey and Water Supply Bulletin - May 15th, 2017

The May 15th snow survey is now complete. Data from 23 snow courses and 71 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 May 15, 2017 Snow Survey Data.
Click here for the Basin Snow Water Index Map.

Weather
Weather through the first half of May has been mixed, and has included periods of hot weather, thundershowers, and episodes of seasonally cold temperatures, including freezing conditions at elevation. The first week in May featured hot weather, particularly in southern BC, which led to rapid melt of mid-elevation snow. This was followed by severe thundershowers. In the second week of May a cycle of wet and cold weather dominated, with heavy precipitation occurring in the Peace region and Bulkley Valley. This also led to light snow accumulations across high terrain across much of the province. The third week of May saw a high pressure ridge build over the province, bringing well-above seasonal temperatures and more rapid snowmelt. Overall, precipitation for the first half of May has been well above normal and temperatures near normal to slightly below normal across the province.

Snowpack
As was observed in the May 1st snow survey period, the snow melt season was delayed by 1-3 weeks in most areas of the province. Warmer weather in early May led to significant melt of mid-elevation snow, and this melt has been sustained throughout the month. At higher elevations, melt began at the start of the month, but cool temperatures in the second week of May led to some minor additional accumulation. Snow line elevations are in the 1500-1600m level through much of the Interior, and likely lower in the Coast Mountains and on Vancouver Island. While mid-elevation snow survey locations (<1500m) have seen most or all of their snow melt by mid-May, many higher elevation sites (>1600m) have only melted 5-15% of their total accumulated snow from this season. In many regions of the province the transition at snowline from areas with no snow to areas with deep snow packs is dramatic. Note that while data used in the analysis for the May 15th snow bulletin indices is from the May 15th survey period, additional snow conditions observed at the automated snow weather stations sites through May 23rd are taken into consideration.

Snow basin indices for May 15th 2017 range from a low of 57% of normal in the Stikine to a high of 157% of normal in the East Kootenay (Table 1 and Figure 1).

Below-normal snowpack (65-80%) is present in the Upper Fraser and Peace, and well below-normal (<65%) in the Stikine. Near-normal snowpack (90-115%) is present in the North Thompson, Central Coast, Upper Columbia, and Vancouver Island. Elevated snow packs (>120%) are present in other areas of the province, including the Nechako, Middle Fraser, Lower Fraser, South Thompson, Kootenays, Okanagan, Boundary, Similkameen and South Coast. High snow basin indices for May 15th are reflective of a delay in the onset in snow melt season this year, particularly at higher elevations, as well as higher than normal seasonal accumulations. Conditions have not changed significantly since May 1st, with snow melt rates over the past 2-3 weeks being typical for this time of year.

Table 1 - BC Snow Basin Indices – May 15th, 2017


Basin

% of Normal

Basin

% of Normal

Upper Fraser West

NO DATA

Boundary

139

Upper Fraser East

78

Similkameen

149

Nechako

127

South Coast

133

Middle Fraser

122

Vancouver Island

104

Lower Fraser

147

Central Coast

91

North Thompson

114

Skagit

NO DATA

South Thompson

122

Peace

79

Upper Columbia

102

Skeena-Nass

NO DATA

West Kootenay

156

Stikine

55

East Kootenay

157

Liard

NO DATA

Okanagan

151

Northwest

NO DATA

Streamflow
With extremely wet weather through the spring in southern BC, most rivers are flowing well above normal for early May, including extreme flows and flood conditions in areas of the Middle Fraser, South Thompson, Okanagan, Similkameen, Boundary, Peace and west-central BC.

On bigger river systems of the province, the seasonal rise of river levels is progressing. Flows on the Fraser River have been near normal for this time of year, and approximately 22% of the forecasted April to September runoff volume has passed through Hope. Similar conditions have been experienced in the upstream tributaries of the Fraser River, including the North Thompson River. Flows on the South Thompson River have been above normal, due to both high snow melt rates in tributaries and persistent wet weather through the region.

Outlook
High elevation snow pack is still sufficient to provide on-going flood risk across the province. On larger rivers and areas draining high elevations, including the North Thompson, Fraser, Kootenay, Columbia, and Skeena, snow melt is expected to lead to increasing flows over the next 2-3 weeks (mid-June). In the South Thompson this period may be 3-4 weeks (late-June). In the Central Interior and South Interior, snow pack is dwindling at mid-elevations, leading to decreasing flood risks. This is the case for the upper Nicola River (inflows into Nicola Lake), Bonaparte River and smaller tributary streams in the Cache Creek, Kamloops, North Okanagan and Central Okanagan areas. In areas of the Central Interior and South Interior which feed from higher elevation areas, flood risks are expected to remain elevated over the next one to two weeks. This includes: Coldwater River; downstream areas of the Nicola River; Similkameen; Tulameen; Mission Creek; areas around Penticton and Oliver; Boundary including Kettle River and Granby Rivers; and inflows into Okanagan Lake. Rainfall, and in particular extreme rainfall amounts or intensities, poses additional risks.
Current weather this past weekend and expected weather through this week is expected to continue to create high flow conditions, particularly in the southern parts of the province.

Current advisories, warnings, freshet information, hydrometric monitoring, river modelling and snow data are available on the River Forecast Centre website: http://bcrfc.env.gov.bc.ca/.

The River Forecast Centre will continue to monitor snowpack conditions and will provide an updated seasonal flood risk forecast in the June 1st, 2017 bulletin, which is scheduled for release on June 7th.

BC River Forecast Centre
May 23, 2017