Storm after storm has brought an abundance of moisture to the coast and mountain snow to the higher terrain this past winter season across B.C., and for that, you can thank La Niña.
La Niña is a weather pattern that occurs when sea surface temperatures across the eastern equatorial part of the central Pacific Ocean are cooler than normal. This can affect global weather patterns, and in B.C.’s case, it means a rainy and snowy winter season. Winter sports enthusiasts must be thrilled so far this season, but the downside is an elevated risk of spring flooding.
JUST HOW MUCH SNOW HAVE WE RECEIVED THIS SEASON?
If you are a skier or snowboarder, then you know that it’s been a fabulous year for powder on the mountains in B.C. The average of all snow measurements across the province is currently at 114 per cent of normal, up from 111 per cent in February, according to the B.C. River Forecast Centre’s snow survey and water bulletin posted on March 1st. The following information was posted in the report:
Regions with normal to slightly above-normal snowpack (100-110 per cent) include the Upper Fraser East, Middle Fraser, South Thompson, East Kootenay, Vancouver Island, and Peace.
Above-normal snowpack (110-125 per cent) is present in the Nechako, North Thompson, Upper Columbia, West Kootenay, Boundary, Okanagan, Nicola, Similkameen, South Coast, Skagit, Skeena-Nass, Stikine and Liard.
Regions with well above-normal (at least 125 per cent) snowpack are the Upper Fraser West, Lower Fraser, Central Coast and Northwest.
WHAT ARE THE VARIABLES THAT GO INTO PREDICTING FLOODING?
La Niña years have resulted in significant flooding in B.C., including 2017, 2012 and 2011, but though those years had similar characteristics, that doesn’t mean flooding is guaranteed.
B.C. River Forecast Centre Hydrologist Jonathan Boyd told me he believed there would be “some versions” of flooding somewhere in the province, and goes on to say: “one region's best-case scenario for weather conditions might be another region's worst-case scenario. That being said, it starts with the snowpack but then it becomes more about the weather conditions.”
When it comes to those weather conditions, I guess that's where my job comes into play – Will it be a hot April, followed by a cool May? How does the precipitation affect the spring runoff and snowmelt? All of these variables play a major role in whether or not we see minimal or major flooding across the province year to year.
I’ve learned that it is really all about balance. A slow melt with short warmups, followed by cooler conditions. is really ideal, according to Boyd. This allows the snowpack to gradually melt. Precipitation that is not extreme is important to have to reduce the risk of flooding. If we experience heavy rain and snow events, this could lead to the risk of flooding.
THE WEATHER NETWORK IS CALLING FOR A WET SPRING
It's true – based on our spring seasonal forecast, it would not be an ideal scenario for mitigating flooding risk across B.C. A cooler pattern could delay the spring melt, which isn’t horrible as long as it isn’t followed by an extremely hot pattern later. The fact that we are calling for a wet season could result in more snowpack and more rainfall, which heightens the risk of flooding.
The B.C. River Forecast Centre releases its next bulletin on April 1st. Check back here or on their website to find out more about potential flooding in your area.