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B.C. winter outlook: Does a La Niña climate pattern mean lots of snow?

Click to play video: 'B.C. evening weather forecast: Dec. 6' B.C. evening weather forecast: Dec. 6
Meteorologist Kristi Gordon has the winter outlook in the Dec. 6 forecast. – Dec 6, 2021

There’s nothing like the first blast of snow across the South Coast to get everyone either excited, or dreading, what December weather will bring.

So, let’s take a look at the upcoming winter forecast for B.C.

First, La Niña is definitely at play.

According to NOAA’s Climate Prediction Center, “La Niña is likely to continue through the northern hemisphere winter 2021-22 (90% chance) and into spring 2022 (50% chance during March-May).”

Read more: How La Niña and climate change may be enabling our current parade of atmospheric rivers

This is the second year in a row, which is common for La Niña years. It’s called a double dip.

British Columbia experienced a ‘fairly typical’ La Niña season last year, with a moderate strength La Niña signal. And it looks like the province could be heading into another.

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La Niña winters typically bring above-average precipitation and below-average temperatures to Western Canada.

Most would assume this means a winter with a lot of snow. While the result is most often above-average snowfall in the mountains, which is fantastic for skiers, it doesn’t necessarily mean snow at lower elevations.

For example, last year, there was very little snow on the ground in Interior valleys, and it snowed only five days at the Vancouver Airport. And three of those days recorded only trace amounts.

The only two days with significant snow across the Lower Mainland were during the Family Day weekend. And that was welcomed fun, as, at the time, local pandemic travel restrictions were in place.

Having said that, B.C.’s last La Nina ‘double dip’ was 2016-17 and 2017-18, where those winters brought a ton of snow to Greater Vancouver.

Essentially, it’s unknown how much snow Vancouver will receive; it could go either way, so motorists should be prepared, especially if hitting the slopes are in the plans.

Here’s a more technical explanation of how B.C.’s winter weather is influenced by La Niña.

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First, La Niña winters are typically wetter than normal in B.C., with many moisture-laden systems hitting the South Coast. Here’s why:

During a La Niña season, cold water upwelling occurs in the eastern Pacific near the equator. According to NOAA’s National Ocean Service, this can push the jet stream northward, making B.C. the target of storms riding along the jetstream.

Current Sea Surface Temperature Anomaly courtesy of the NOAA View data imagery portal.

In addition, the jetstream can become more active due to enhanced warm waters in the western Pacific, specifically the Indo-Pacific warm pool.

This expanded warm water can increase convective activity, ushering moisture to high altitudes and increasing the ability of the jetstream to transport moisture from the Pacific to B.C.

Second, the province tends to be on average colder than normal. Here’s why:

“During La Niña, the Aleutian low is much weaker,” says B.C. climatologist, Faron Anslow.

This enables a weaker polar jet — higher than normal pressure over the Aleutians and lower than normal pressure over B.C.

La Niña causes the jet stream to move northward and to weaken over the eastern Pacific. During La Niña winters, the north and Canada tend to be wetter and colder than normal. Global BC

This combination of factors can cause the weakened polar jetstream to often stall as a ‘blocking high pressure’ ridge develops off B.C.’s coast.

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This “means that storms are steered from a more northwesterly direction,” across B.C. says Anslow, “favouring colder temperatures.”

Read more: From ‘beached’ snow orcas to snowboarding in the streets, B.C. residents are embracing the snow

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