The April 1 snow survey from the River Forecast Centre states “there are no regions in the province with normal or above normal snowpacks”.
The report notes that following an extremely cold February, temperatures were mixed across British Columbia in March. Cooler temperatures dominated the first half or more of the month in most areas. A warm spell towards the end of March brought record or near-record high seasonal temperatures, particularly in southern BC. Despite this warm spell, overall monthly temperatures were near-normal to below normal (+0.5 to -3 ̊C) through most of the southern two-thirds of the province. In the far north, temperatures were well above normal, with Fort Nelson experiencing the warmest March on record (March temperature anomaly of nearly 6 ̊C above normal).
March was one of the driest on record for areas in the south-west and north-east. Precipitation ranged from five per cent to 70 per cent of normal, with most areas in the province receiving less than 25 mm of precipitation through the month.
Snow pack for April 1, ranges from a low of 47 per cent of normal in the Northwest to a high of 94 per cent in the Upper Fraser West, with the average of all snow measurements across the province calculated to be 79 per cent of normal. A well-below normal snowpack (60 per cent of normal) is present in the Stikine, Northwest and Skagit. A below normal snowpack (60-80 per cent of normal) exists in the Liard, Skeena-Nass, Nechako, Central Coast, South Coast, Lower Fraser, Vancouver Island, Similkameen, Nicola, Okanagan, South Thompson, Boundary and East Kootenay. The rest of the province has slightly below normal to normal snowpack (80-95 per cent of normal). The North Thompson is at 89 per cent, and the South Thompson is at 75 per cent.
Most of this year’s snowpack built up rapidly over a five to six-week period during early December to early January. Weather through February was dominated by Arctic air across the province, with extremely cold temperatures and limited snow accumulation. This pattern was continued into the beginning of March. Extremely dry weather through March led to very little snow accumulation through the month. In low and mid-elevations (<span class=”n_ 954 v3″>1500m), hot weather led to snowpack ripening and early season snow melt.
Streamflow
With persistent dry weather in March, rain-dominated rivers in coastal areas of B.C. have been experiencing extremely low, and in some cases record low, seasonal levels. This has been primarily due to the extremely dry weather in regions that typically experience wetter weather through February and March. Cold also played a role, as freezing temperatures at low elevations inhibited runoff.
Warmer temperatures towards the end of March led to melt of low elevation snowpacks. In coastal areas, this led to modest increases in streamflows, which still remain well below normal for this time of year. In the B.C. Interior, warm temperatures have led to the early onset of freshet, and rivers have been receiving snow melt runoff. Early April streamflow is generally above normal, or well above normal across the Interior, reflecting the onset of freshet two to four or more weeks ahead of normal.
Outlook
The Climate Prediction Centre (CPC) at the National Oceanic and Atmospheric Administration’s (NOAA) National Weather Service (NWS) has declared that El Niño conditions are present and sea surface temperature anomalies in the equatorial Pacific Ocean have strengthened since the beginning of February. NWS continues to forecast a high likelihood of El Niño continuing through spring 2019, and potentially extending into the summer and fall periods. Typically, El Niño is linked to warmer winters across B.C., with a trend towards a lower than normal snowpack.
While this year’s low snowpack follows this trend for El Niño winters, low snowpacks are not the result of warmer winter temperatures typically expected during El Niño winters; instead, this year has featured persistent colder than normal temperatures and extremely dry weather through February and March, leading to the observed low snowpack across the province.
Seasonal forecasts from Environment and Climate Change Canada favor a high likelihood of above normal spring temperatures (April-May-June) across B.C., particularly along coastal areas.
Annual snow accumulation in B.C. usually reaches maximum levels in mid-April. Currently, the snow accumulation ranges from well below normal to normal across the province.
The report notes that at this stage in the season there is no elevated flood risk present in the current snowpack across the province.
Normal seasonal flood risk is expected in the Peace, Upper Fraser and North Thompson. With below normal snowpack in most regions, reduced flood risk is expected.
Snowpacks at low elevation have already melted, and snowmelt has been observed at mid-elevation (<span class=”n_ 965 v3″>1500m). Melt is expected to occur soon at higher elevation, unless a significant cold weather pattern emerges in the next couple of weeks. Current conditions indicate the potential for an extremely early spring melt and freshet season; these current conditions typically occur two to six weeks from now.
With an increased likelihood of above normal temperatures persisting through the spring, the trend of early melt is expected to continue.
This suggests that the next two to four weeks may be the critical window for freshet for medium-sized and mid-elevation rivers across the province, and early-to-mid-May for larger rivers.
This is much earlier than is typically experienced, and with previously experienced warms spells in March and associated low snowpacks throughout the province, there is the potential that snowmelt will be unprecedentedly early this season.
The River Forecast Centre will continue to monitor snowpack conditions and will provide an updated seasonal flood risk forecast on May 8, 2019.
Source: River Forecast Centre
