Strongest ridge in 60 years, what makes this so unusual?
Thursday, September 27, 2018, 5:52 PM - This isn't a run-of-the-mill anomaly, or an ordinary ridge of high pressure. The resiliency and amplitude of the ridge that blossomed over parts of Alaska in early September is one for the record book, so what's going on?
- September 1st-20th: most positive 20-day height anomaly on record anywhere in the northern hemisphere
- Strength of ridge has had a profound impacts downstream, specifically the Prairie provinces
- Ridge approximately 5 standard deviations from what's considered normal
Can we really lay some blame towards this ridge on why Alberta has been so cool and at times snowy this September? Yes, it's much easier to move colder air from the poles in a high amplitude pattern, such as the setup the past several weeks across North America.
Cold air situated near the pole is forced southwards with such an anomalous pattern, and that high pressure ridge in question hasn't budged in weeks over Alaska. To the east, a conduit for colder temperature anomalies develops to effectively push below seasonal air further south with extreme vigor and ferocity for September.
How can we be sure that this ridge is in fact the extreme anomaly stated above?
Meteorologists and climatologists on Twitter were quick to point out how impressive this anomaly truly was:
This is extremely substantial event for this 500mb ridge, nestled in the middle of the atmosphere, approximately 5000 metres above sea level. But it isn't the strength of the ridge, although impressive, it's the length of the persistent blocking pattern in the atmosphere. For those who crave some more detail about this historic event, look no further than this detailed blog post, by Richard James and Rick Thoman.
MORE CONSEQUENCES AHEAD?
Yes, all you have to look at is the 10 day snowfall outlook across parts of Canada, downstream of this mega ridge. Prepared to be shocked:
Quite an early start to building some of the snowpack across northern Canada, and the foothills in Alberta in particular. But as we trek through October, the pattern will relent, and warmer air will eventually work its way into the Prairies.
In fact, it may be possible that October in the Prairies is a warmer month, by mean temperature, than September, which is highly unusual with the fading sun angle and typical seasonal patterns experienced during fall.