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South Okanagan Photos

Freshet over? – snowpack low

Snowpack

The provincial snow pack has continued to melt at a rapid rate. Most snow survey locations experienced 150-300 mm of snow water equivalent loss over the May 15th to June 1st period. With the heat spell over the past several days, snow melt rates observed at automated snow weather stations have been in the 35 to 75 mm/day range.

Snow basin indices continue to decline relative to normal values, reflecting the extremely early melt this season. June 1st snow basin indices range from 2% to 69% (Table 1). Snow basin indices are extremely low (<50%) for most regions in the province, except in the North Thompson, South Thompson and Upper Columbia which are at 60-70% of normal.

snowpak june

1. ‘No Data’ indicates that no snow surveys were conducted within the basin during this survey period

The provincial average index for June 1st is 23%, and is a record low for this time of year based on records to 1980. Nearly half of all observations from June 1st recorded little or no snow.

Streamflow

Freshet runoff echoes the pattern in snow melt, with many rivers experiencing flow conditions that are 3-4 weeks or more ahead of normal conditions. While April runoff was generally well above normal across the province, flows eased to near normal for May as rivers transitioned to the declining limb of the snow melt runoff cycle. Rivers across the Interior of BC are expected to see lower than normal runoff through the rest of the season, particularly in June-July when runoff is usually still strongly influenced by snowmelt.

Outlook
Seasonal forecasts from Environment Canada are indicating an increased likelihood of above-normal temperatures across British Columbia over the June to August period. Most rivers in the province have likely experienced their peak flow for this season, and freshet flows are now receding. Seasonal flood risk due to snow melt is now limited across the province, however flooding could still occur from significant rainfall events.

The advanced freshet is expected to put pressure on summer low flows in snow-melt dominated rivers across the province.

Current forecasts for the week suggest a transition out of the hot spell experienced last weekend as a cold low moves across the province. This is expected to bring cooler temperatures and moderate rainfall.