Snow Survey and Water Supply Bulletin – March 1 st , 2020 1. 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 upon review. Executive Summary Mixed weather through February has led to on-going development of the province’s snowpack. The provincial average of snow measurements is 111% of normal, a slight increase from 110% of normal on February 1 st , 2020. The snow basin index for the Fraser River is 117%, with high snow pack levels in it’s major tributaries. Seasonal flood risk is elevated in many regions, including the Upper Fraser West, Upper Fraser East, North Thompson, South Thompson, West Kootenay, Boundary, Central Coast and Skagit. Typically, 80% of the annual snow accumulation has occurred by March 1 st , with another 4- 8 weeks of snow accumulation still to come. While changes to the overall provincial seasonal flood risk are possible over the next few months (either increases or decreases), current trends in snowpack are likely to persist. Snow pack is one element of seasonal flood risk in BC, however snowpack alone does not predict whether flooding will occur; spring weather is a critical factor determining the rate that snow melts, while extreme rainfall can also cause spring flooding independent of snow conditions. Overview The March 1 st snow survey is now complete. Data from 131 manual snow courses and 82 automated snow weather stations around the province (collected by the Ministry of Environment 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 1 . Weather An atmospheric river event impacted British Columbia at the start of February, with warm temperatures and extreme rainfall leading to flooding on Vancouver Island and the South Coast. Weather patterns were mixed through the rest of the month, with periods of north- west flow (cooler and moister conditions) and high pressure (cooler and drier). Monthly temperatures across BC were mixed, with many areas being near normal (monthly temperature anomalies of -1˚C to +1˚C), particularly in coastal areas of BC. Warmer than normal temperatures (+1˚C to +3˚C) were present to in the South Interior, Central Interior and Northern BC. Precipitation was more modest across BC in February, following a wet January. Coastal areas, including Vancouver Island and the South Coast, had below normal precipitation. In the BC Interior February precipitation was near-normal to above-normal for most areas.
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Snow Survey and Water Supply Bulletin – March 1st, 2020
1. 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 upon review.
Executive Summary Mixed weather through February has led to on-going development of the province’s snowpack. The provincial average of snow measurements is 111% of normal, a slight increase from 110% of normal on February 1st, 2020. The snow basin index for the Fraser River is 117%, with high snow pack levels in it’s major tributaries. Seasonal flood risk is elevated in many regions, including the Upper Fraser West, Upper Fraser East, North Thompson, South Thompson, West Kootenay, Boundary, Central Coast and Skagit. Typically, 80% of the annual snow accumulation has occurred by March 1st, with another 4-8 weeks of snow accumulation still to come. While changes to the overall provincial seasonal flood risk are possible over the next few months (either increases or decreases), current trends in snowpack are likely to persist. Snow pack is one element of seasonal flood risk in BC, however snowpack alone does not predict whether flooding will occur; spring weather is a critical factor determining the rate that snow melts, while extreme rainfall can also cause spring flooding independent of snow conditions. Overview The March 1st snow survey is now complete. Data from 131 manual snow courses and 82 automated snow weather stations around the province (collected by the Ministry of Environment 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 report1. Weather An atmospheric river event impacted British Columbia at the start of February, with warm temperatures and extreme rainfall leading to flooding on Vancouver Island and the South Coast. Weather patterns were mixed through the rest of the month, with periods of north-west flow (cooler and moister conditions) and high pressure (cooler and drier). Monthly temperatures across BC were mixed, with many areas being near normal (monthly temperature anomalies of -1˚C to +1˚C), particularly in coastal areas of BC. Warmer than normal temperatures (+1˚C to +3˚C) were present to in the South Interior, Central Interior and Northern BC. Precipitation was more modest across BC in February, following a wet January. Coastal areas, including Vancouver Island and the South Coast, had below normal precipitation. In the BC Interior February precipitation was near-normal to above-normal for most areas.
Snow Survey and Water Supply Bulletin – March 1st, 2020
1. 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 upon review.
Snowpack Snow basin indices for March 1st, 2020 range from a low of 84% of normal in the Liard to a high of 139% in the Skagit (Table 1 and Figure 1). Most regions experienced steady snowpack growth since February 1st, with the overall average of province-wide measurements increasing slightly from 110% of normal last month to 111% of normal for March 1st. Table 1 - BC Snow Basin Indices – March 1, 2020
Basin % of Normal Basin % of Normal
Upper Fraser West 135 Boundary 134
Upper Fraser East 135 Similkameen 112
Nechako 104 South Coast 101
Middle Fraser 99 Vancouver Island 93
Lower Fraser 94 Central Coast 136
North Thompson 123 Skagit 139
South Thompson 127 Peace 119
Upper Columbia 115 Skeena-Nass 93
West Kootenay 121 Stikine 104
East Kootenay 110 Liard 84
Okanagan 115 Northwest 100
Nicola 88 Fraser 117
British Columbia 111
High snowpacks are generally present in the mountainous interior ranges of the province, with coastal areas (except for the Central Coast) seeing nearer-to-normal conditions. The Upper Fraser – West, Upper Fraser - East, Cariboo Mountains (Quesnel River), North Thompson, South Thompson, West Kootenay, Boundary, Central Coast (Bella Coola) and Skagit basins all exceed 120% of normal snow. Moderately high snowpack (110-120%) is also present in the Upper Columbia, East Kootenay, Okanagan, Similkameen, and Peace.
Snow Survey and Water Supply Bulletin – March 1st, 2020
1. 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 upon review.
There is a significant east-west divide within the Okanagan; eastern regions of the Okanagan have measurements around 120 to 150% of normal, while measurements in the western portion of the Okanagan range from 75% to 100% of normal. The overall snow basin index for the entire Fraser River basin (e.g. upstream of the Lower Mainland) is 117%. During freshet, the majority of flow (roughly two-thirds) in the Fraser River originates from the Upper Fraser – East, North Thompson, South Thompson and Cariboo Mountains. Cumulative snowpack in these areas is very high (126% of normal), with snowpack in unregulated watersheds of the Fraser River upstream of Hope (e.g. excluding the Nechako and Bridge systems) being among the highest years on record. For perspective, recent years with high snow basin indices for unregulated watersheds of the Fraser River upstream of Hope are 2018 (114%); 2012 (119%); 2007 (124%); 1999 (134%); 1997 (117%).
Outlook
Neutral El Niño Southern Oscillation (ENSO) conditions have been in place since the summer of 2019, with near-normal or slightly-above normal (<0.5˚C) temperature anomalies along the equatorial Pacific Ocean region. Closer to BC, warm temperature anomalies that were present earlier in the fall/winter have been dissipating since January, with cooler than normal temperatures along the BC and Alaska coastlines, and moderately warmer than normal temperatures offshore in the North Pacific. Forecasts from the CPC are indicating a high likelihood (approximately 70-75% chance) of continued neutral ENSO conditions into the spring and early-summer. Neutral ENSO conditions generally have a less predictable association with snow pack and weather conditions in BC, in comparison to El Niño and La Niña conditions. Further, ENSO signals tend to be less pronounced over springtime in BC; springtime ENSO forecasts also tend to be less skillful than at other times of the year. Seasonal weather forecasts produced by Environment and Climate Change Canada in late February are indicating an increased likelihood of cooler than normal temperatures for March through May for most of British Columbia, except in areas of the south coast and along the southern border where the forecast is for increased likelihood of near normal temperatures. Similar seasonal forecasts from NOAA favour near-normal to above-normal temperatures across BC through the spring. Discrepancies between these two models may be an indication that the temperature and teleconnections currently present are creating increased uncertainty over the outlook for seasonal weather this spring. For snow-melt dominated rivers in the interior of the province, the likelihood of spring flooding increases with high snowpacks; this is most pronounced when snow basin index values approach or exceed 120%. This does not mean that spring flooding will occur, rather the chances of flooding are increased. Increased seasonal flood risk is present in the Upper
Snow Survey and Water Supply Bulletin – March 1st, 2020
1. 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 upon review.
Fraser – West, Upper Fraser - East, Cariboo Mountains (Quesnel River), North Thompson, South Thompson, West Kootenay, Boundary, Central Coast (Bella Coola) and Skagit basins. Historically, there are few years where snow pack in the major tributaries of the Fraser River have all been high at the same time (examples include 1972, 1974 and 1999); given the influence of the Upper Fraser and Thompson River for the overall freshet flow on the lower Fraser River, seasonal flood risk for the entire Fraser River is substantial. Seasonal volume forecasts for select watersheds (appended to end of the report) follow similar trends as snow pack. Volume inflow forecasts for the Okanagan system are 151-155% and are significantly higher than the overall Okanagan snow basin index. Similarly, runoff forecasts for the Similkameen River (at Hedley) are at 121%, above the snow basin index of 112%. In other areas, runoff forecasts are lower than snow basin indices, with runoff forecasts for the Nicola at 65-72%, Skeena and Bulkley at 94-98%, and Upper Fraser, Middle Fraser and Thompson tributaries at 108-118%. By early March, nearly 80% of the annual BC snowpack has typically accumulated; high snowpack levels in some regions already exceed normal annual maximum accumulation. With one to two months left for snow accumulation, seasonal snowpacks and seasonal flood risk can still shift. Given the current ENSO neutral conditions, it is reasonable to expect increased uncertainty over seasonal weather for the remainder of this winter and into spring. From a seasonal flood perspective, a scenario of a cool and wet spring would lead to increasing risk over the next 4-8 weeks, whereas a warm and dry scenario may partially alleviate some of the current risk. While snowpack is one risk factor for freshet flooding, snowpack alone cannot predict whether flooding will occur or not. Spring weather is also a critical flood risk factor and the timing and severity of temperature and rainfall patterns are important drivers of flooding irrespective of snowpack levels. The River Forecast Centre will continue to monitor snowpack conditions and will provide an updated seasonal flood risk forecast in the April 1st, 2020 bulletin, which is scheduled for release on April 8th.
BC River Forecast Centre March 9, 2020
Snow Survey and Water Supply Bulletin – March 1st, 2020
1. 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 upon review.
Figure 1: Basin Snow Water Index – March 1st, 2020
Snow Basin Index Graphs ‐ March 1, 2020
103
137142
85
66
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135
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Upper Fraser West Snow Basin Index
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97 95
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Lower Fraser Snow Basin Index
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South Thompson Snow Basin Index
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Middle Fraser Snow Basin Index
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North Thompson Snow Basin Index
96 9991
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Upper Columbia Snow Basin Index
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Upper Fraser East Snow Basin Index
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Nechako Snow Basin Index
Snow Basin Index Graphs ‐ March 1, 2020
9487 83
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West Kootenay Snow Basin Index
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East Kootenay Snow Basin Index
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Boundary Snow Basin Index
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Okanagan Snow Basin Index
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Similkameen Snow Basin Index
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9990
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South Coast Snow Basin Index
101
52
21
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Vancouver Island Snow Basin Index
9081
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7884
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Central Coast Snow Basin Index
Snow Basin Index Graphs ‐ March 1, 2020
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Skagit Snow Basin Index
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Peace Snow Basin Index
89 8592
73 74
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Skeena‐Nass Snow Basin Index
9486
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Stikine Snow Basin Index
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Liard Snow Basin Index
120
78 78 77 73 71
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Northwest Snow Basin Index
March 2020 Automated Snow Weather Station / Manual Snow Survey Data
