Snowpacks across B.C. are above average as of April 1, and while a relatively dry March helped decrease snowpack numbers in the region, warmer temperatures this week could present challenges for smaller creeks and lower elevation areas.
The B.C. River Forecast Centre says that regions with normal to slightly above normal snowpacks include the North and South Thompson and Nicola areas. Above normal snowpack is present in the Upper Fraser East and Lower Fraser areas.
The South Thompson area includes rivers and streams that feed into the Thompson River downstream of Kamloops Lake. At this time last year, the North and South Thompson snowpacks were at their highest levels since 1999. A lengthy snowmelt in 2020, as well as wet weather through April, May, and June, led to a prolonged flood season that did not end until early July.
Some 95 per cent of B.C.’s annual snowpack has accumulated by early April. While the risk of spring flooding is elevated this year due to the above normal snowpack across the province, snowpack alone does not predict whether or not flooding will occur.
Spring weather is a critical flood risk factor: temperature and rainfall patterns are important drivers of flooding, irrespective of snowpack levels.
Since mid-March, temperatures have remained seasonable to slightly below normal for most areas. However, a high-pressure ridge moving in this week will likely result in very warm temperatures for the entire province. While this could impact small, low-elevation creeks, it might be more positive for larger, high elevation watersheds if it brings a steady, earlier melt.
Spring freshet poses a seasonal risk across the B.C. Interior. Scenarios that could exacerbate flood risk this year include prolonged cool weather followed by a rapid shift to persistent hot weather (particularly in May), or persistent wet weather or extreme short-term rainfall.
Favourable scenarios would include continued dry weather and seasonal temperatures over the coming weeks.
You can view the River Forecast Centre’s April 1, 2021 “Snow Survey and Water Supply Bulletin” at https://bit.ly/3mHEkZp.