February 15, 2010 - Blame It On The Block

By: Mallory Brooke
By: Mallory Brooke

Why all the cold air and snow in the Valley, but not so much for Vancouver and the Winter Olympics? Read about it in my blog!

Another round of snow enters the Valley on this President's Day, giving us another chance of accumulating snow. As long as this snow is measurable, we will break records in Harrisonburg.

But the question remains, why is the east coast inundated with snow, yet Vancouver can't get a flake for the Olympics?

The last time we were above 45 degrees was January 28th - and that's seasonal for us. Yet we've been below average and extraordinarily snowy for the past several weeks.

We saw this in late December through the first part of January and once again in the latter part of January and the first half of February. The cold air just won't leave! It's what we call a "Blocking Pattern".

Greenland Block (Courtesy: Weather.com)

High pressure has taken up shop in Greenland and does not want to move. This basically causes a jam in the motion of the atmosphere, called a "Greenland Block" (The image above courtesy of weather.com). Air currents (our jetstream) usually flow from west to east , but when air hits our "blocking high", it has to navigate up and around the high pressure or dig south. With a ridge of high pressure over Greenland, two troughs usually form - one over the eastern US and the other over Europe. Therefore all the arctic air bottled up in Canada can freely travel down to the southern extent of the jet stream, which is sometimes all the way down to Florida.

With the blocking pattern in place, and consequently the cold air in place, we've seen many more snow events this winter. With a trough in the eastern US, a ridge is in place in the western US, thus affecting the weather in Vancouver. Instead of receiving the cold air from the Arctic, it's receiving warmer air from the US, therefore keeping temperatures higher than average and snowfall to a minimum.

 Monday's Jet Stream (Courtesy: AccuWeather)

 Tuesday Jet Stream (Courtesy: AccuWeather)

Above are the jetstream patterns for Monday, Feb 15 and Tuesday, Feb 16 as shown by AccuWeather. Sometimes the blocks last for days, sometimes for weeks. In our case, it has been weeks, and may be going on months before all is said and done.

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