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Snowpacks low for this time of year in Okanagan and Similkameen basins
The snowstorms that continued over the past week make it easy to overlook a drier trend in January that has caused snowpacks to fall below normal.
In the Okanagan Basin, snowpacks were down to 79 per cent of normal and in the Similkameen they were at just 73 per cent, based on B.C. River Forecast Centre data released last week.
The level of winter snowpacks is used to help forecast the likelihood of spring floods and summer water supply.
The key factor in determining summer streamflows, however, is the weather in spring and summer.
The snowpack figures reflect conditions as of Feb. 1.
“January was a dry month across the province with below-normal precipitation across most of the province and well below-normal precipitation in southern and northeast B.C.,” says the Feb. 1 Snow Survey and Water Supply Bulletin.
In the Okanagan, the snow basin index is lower than for this time in other recent years, well below the 92 per cent level at this time in the drought year of 2015.
In the Similkameen, the index is also lower than it’s been at this time of year in any year since 2010.
The River Forecast Centre points out that there are still two to three months remaining in the snow accumulation season and changes to the seasonal runoff outlook are possible.
“But at this stage, [it] would require extremely wet conditions to make a significant impact on seasonal flood risk,” the bulletin says. “In most regions of the province, spring and summer weather is the key driver for low summer streamflow.”
Over the last two years in particular, an early melt and warmer spring weather led snowpacks to decrease rapidly.
In 2015, this contributed to drought conditions, while in 2016, larger snowpacks, rain in late spring and good water management minimized the problem of drought.
In January, temperatures ranged from 0.5 to 3.0 degrees Celsius below normal in most of southern and southeast B.C., while temperatures were well above normal through most of northern B.C.
Environment and Climate Change Canada is predicting an increased likelihood of near-normal temperatures across most of B.C. over the February to April period.
Colder temperatures were forecasted for early February, with a transition to warmer-than-normal conditions into the middle of the month.
“By early February, two-thirds of the annual B.C. snowpack has typically accumulated,” the bulletin said. “At this stage in the season, there is limited indication that any region of the province is developing increased seasonal flood risk due to high snowpack.”
Snowpack is an important factor in seasonal flooding, but weather during the melt season can also create flood risk, such as hot temperatures causing rapid snowmelt or extreme rainfall events.