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June 25, 2019

Snow Survey and Water Supply Bulletin

The June 15st snow survey is now complete. Data from four manual snow courses and 80 automated snow weather stations around the province (collected by the Ministry of Environment and Climate Change Strategy Snow Survey Program, BC Hydro and partners), and climate data from Environment and Climate Change Canada and the provincial Climate Related Monitoring Program have been used to form the basis of the following report.   A complete version of this report, including full survey data, snow basin map, seasonal forecasts and comparison with previous years is available on the River Forecast Centre website at: https://www2.gov.bc.ca/gov/content/environment/air-land-water/water/drought-flooding-dikes-dams/river-forecast-centre/snow-survey-water-supply-bulletin   A web-version of the provincial snow basin index map for June 15th is available here.   Weather Weather through early-June has been mixed across the province. Temperatures in southern BC have generally been above normal, particularly in the South Interior and Kootenays. Central BC has had closer to normal temperatures, while areas in the central-west and north-west have been below normal.   A number of typical seasonal precipitation events have occurred in June, and have brought some rainfall to the province, particularly along the Central and North Coast areas. Other areas of the province have generally been drier than normal, including well below normal precipitation in the South Coast, Vancouver Island and South Interior.   Snowpack   Snow basin indices for June 15th have continued to drop significantly as a result of warm temperatures and rapid snowmelt; few snow courses still indicate the presence of snow as of June 15th. Snow basin indices for June 15th, 2019 range from a low of 0% of normal to a high of 44% in Upper Fraser East (Table 1 and Figure 1), with the average of all snow measurements across the province calculated to be 21% of normal.   Snowpack is extremely low (<50% of normal) in all areas of the province. Extremely low % of normal values in June usually stem from early snowmelt. This is the case for 2019, where low snowpack during June (both the June 1st and 15th bulletins) reflects melt that is 1-3 weeks ahead of normal for most areas. The early melt season began with two weeks of above normal temperatures in mid-March, which melted low elevation snow and primed snowpacks at all elevations to melt. This warm period was followed by lower than normal seasonal snow accumulations – for example, the average snow water equivalent measurement on April 1st  was 79% of normal. This year’s June 15th snowpack across the province is like conditions experienced in 2015 and 2016 – both years with early melt.   Typically, two-thirds of the accumulated seasonal snowpack in BC has melted by June 15th. This season’s early melt means that 55-100% of the snowpack at most sites has already melted. Indeed, many sites across the province indicate that 100% of the snow has melted, with snow present only at select sites across the province; these sites tend to be at high elevations (>1700 m).   Note that in the later part of the snow season, basin indices can become extremely low due to early melt, and comparison of little or now snow relative to a normal snow water equivalent that is also low relative to the annual accumulation. Caution should be exercised when interpreting snow basin indices at this time of year.   Table 1 – BC Snow Basin Indices – June 15st, 2019

Basin % of Normal Basin % of Normal
Upper Fraser West No data Boundary 0
Upper Fraser East 44 Similkameen 0
Nechako 0 South Coast 20
Middle Fraser 18 Vancouver Island 2
Lower Fraser 3 Central Coast 1
North Thompson 31 Skagit No data
South Thompson 19 Peace 14
Upper Columbia 39 Skeena-Nass 16
West Kootenay 37 Stikine No data
East Kootenay 10 Liard No data
Okanagan 0 Northwest No data
Nicola No data Fraser 19

Streamflow Current streamflow is variable across the province, depending on the location, size of watershed, and key hydrological processes of rivers. Rivers that depend on snowmelt across the province have recently peaked and are receding as snowmelt contributions to streamflow decreases.   In coastal British Columbia, including most areas of Vancouver Island, Haida Gwaii, and lowland rivers in the South Coast, streamflow is extremely low for this time of year. This is the result of rivers having minor influence from snowmelt, and both short-term and persistent long-term dry conditions. For example, most rivers on Vancouver Island are currently flowing below 5th percentile flows for mid-June, and several rivers are at record low flows for this time of year.   In most areas of the BC Interior, snowpacks have been depleted and rivers are on the receding limb of the seasonal freshet hydrograph. With the combination of low seasonal snowpack, dry spring weather, and early melt, current streamflow conditions in these areas is similar to conditions that are experienced late-July or early-August, rather than mid- June. In some areas streamflow is approaching or exceeding record lows for this time of year. Outlook   Seasonal forecasts from Environment and Climate Change Canada favor an increased likelihood of above normal summer temperatures (June-July-August and July-August-September periods) across British Columbia. In the short-term, BC is forecast to experience seasonal conditions, which include the potential for more organized rainfall.   With diminished snowpacks and early melt this year, risks have shifted towards the increased likelihood of low flow conditions this summer in all areas of the province. Given generally drier weather, warmer temperatures, low snowpacks and early melt this season, risks of low flows this year are significant across the province.   In most areas of the province, continued decline in flows are expected in the short-term, driven by drier weather (particularly on Vancouver Island and the South Coast) and the waning influence of snowmelt runoff (in the BC Interior). More organized rainfall may lead to improvement in streamflow in some areas of the north-east.   While antecedent conditions are one important factor for summer low flows, summer weather is also of critical importance. Long-range precipitation is difficult to forecast accurately over long lead times, therefore creating uncertainty over how the 2019 summer season will play out. While continued dry weather would drive extremely low flows this season, there is a similar chance that wet weather could dominate the summer season and at least partially ease the risk of low flows.   Current information on drought, including provincial drought levels, is available on the British Columbia Drought Information Portal.   This is the final snow bulletin for the 2019 season; the first snow bulletin of the 2020 snow season will be released in early January, 2020. Thank you to our partners for their contributions to these bulletins.   BC River Forecast Centre
June 21, 2019