El Nino years have a habit of throwing a curve ball into the weather regime just to keep us on our toes. The early (but not record breaking) freeze that just concluded was a close call with truly arctic weather that would have been a catastrophe.
If unmodified arctic air had blanketed the region with widespread highs in the 20’s and lows in the teens such had happened in the infamous early freezes of 1955, 1978, and 1985 and those events resulted in wide spread damage killing and mangling even perfectly hardy plants which were shocked with no proceeding freezes to transition them into dormancy. As proof of the threat of extreme up and down conditions, even native plants are damaged when this happens.
This condition of the atmosphere is called an Omega Block. It sets up shop and completely diverts the jet stream which must go around this and it sends the flow on a one way ticket straight from the arctic. An omega block over Alaska- such as we have now appeared in October 2006. In that year it only amounted to one single night of extreme cold which mitigated hard core damage. This pattern forces extensions of the ever occurring polar vortex south over almost the entire continent. This time the perturbation in the jet stream was massive and it sent a huge volume of incredibly arctic air blasting south and reaching on its western periphery sloshing over the Rockies and then drawn over the mountains and through the Columbia Gorge. For almost 24 hours straight the wind at PDX gusted over 40mph roaring from the east.
We had just passed through the warmest August, September, and October in Portland history. The majority of the rain that fell in October was derived from the tropics and the warmer than normal readings bore this out. A rapid transition to temperatures much colder than we actually had (27ºF at PDX and 19ºF at Vancouver and Hillsboro were our coldest), plants would have been fat and ripe for cold damage.
Also- the second bout of arctic weather last winter that appeared in the first week of February had almost 8 hours of subfreezing strong wind (19ºF with 50MPH gusts) and that resulted in profound damage on plants already weakened by the December freeze. This time there was no subfreezing wind. But the wind, gusting as high as 55mph was damaging enough.
I hope your gardens have been put to rest and that they sleep soundly through winter. As of the beginning of the month we are officially in a mild El Nino with index just barely nudging toward the warmer phenomenon. May mulch be with you and also with you. It will be interesting to see if this was our coldest weather of the entire winter season. That wouldn’t be unusual at all.
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