A butterfly farts and we get the coldest winter in 15 years.

Right after i hit send on my last blog ‘El Nino is here in Force’ i began to hear about the record cold that enveloped China in early December. It resulted in the coldest weather in that country in 100 years and it broke several conspicuous  long standing cold records including the coldest temperature ever officially recorded there -56ºF. Several weeks later a deep arctic trough plunged from Scandinavia south to Greece and Egypt, another deep outbreak of arctic weather that held some of the coldest temperatures in 50 years. As it  surged south it affected  all of central and eastern Europe with paralyzing cold and blizzards.  What these two cold waves indicated is that we were looking at a more unstable, wavier jet stream this year and despite the warmest year globally  perturbations of the polar vortex were on the docket and may be enhanced by global warming.  And though it was but a foot note in all winter forecasts, nearly all including the NOAA and private forecaster stuck stubbornly to a warmer than normal winter. OOOOOPS, but forgot to mention that arctic outbreaks are about a 30% likelihood during an El Nino and more than that during a major El Nino and i along with everyone else fixated on the warmer than normal year. Winter forecasts aside and its still likely that the majority of our winter excluding the 7 arctic days in January, will be milder than normal, almost warm.

The Polar Vortex is a real thing

The polar vortex is a large area of cold low pressure that always sits on top of the earths poles at 10 to 30 miles aloft.  It gains strength in winter and weakens considerably in summer. If the polar vortex is strong or stable the counter clockwise flow of the polar jet stream traps this cold air at the poles. The jet stream moves smoothly in a circle. When the jet stream becomes perturbed it allows the polar vortex to sag or split pouring arctic air astonishingly far south. This perturbation of the polar jet stream is caused  by what is known as SUDDEN STRATOSPHERIC  WARMING. These are heatwaves that occur as warm air surges north into the polar regions sometimes as much as 50ºC  warmer in a day.   Warm air moves rapidly north into the polar region and pushes or more appropriately it sloshes the cold air displaced at the poles south and results in deep and record breaking arctic outbreaks over the continents on the opposite sides of the globe. Some of our greatest cold waves were initiated by this , 1977,1982, 1985, 1989,1998 2014,….and the infamous 2021 Texas cold wave which nearly snuffed out their power grid and saw subzero temperatures cross the Rio Grande into  Mexico and resulted in hundreds of deaths.

Global warming leads to global cold

It’s still up for some debate but the chemical changes that happen in the stratosphere and troposphere to perturb the jet stream is most likely being enhanced by global warming. The fact that  sudden stratospheric warming (SSW)  is happening more often is not up for debate. It is. Also the polar vortex is not a new term or condition, in fact it earned that name way back in 1953- only  as the  public’s understanding of weather phenomena has increased so has  its ability  to latch  on to more specific weather terms.  The press literally pulled this term out of  the NOAA to dramatize winter storms. The first broad coining of this term was in the arctic outbreak of 2014.

Arctic outbreak 1/24

Here is a map Greg made of the lowest temperature at each recording station in the metro: Notice the coldest air near the Gorge and in the west hills. Also a stretch of very cold air into south east PDX into down town. Low 12ºF.Temperatures are warmest away from the Gorge. The coldest day at PDX had a high of 21ºF and a low of 15ºF for two consecutive nights

Damn subfreezing wind

I’ve gardened in Portland for more than 25 years. I’ve been  through at least 8 major freezes and I can say that subfreezing wind is the Achilles heel of gardening in the metro. I learned to garden in Eugene where there is no howling ,desiccating sub zero wind – in fact its almost always calm during arctic cold. That actually  allows it to get colder,  wind keeps the atmosphere stirred and warmer  so it  might be 15ºF in Portland with 35mph winds and 5ºF and calm in Eugene and you get the same amount of damage to plants. Wind easily erodes hardiness and its catastrophic in an almost exponential way when combined with low temperatures. Broadly i start to be concerned at 28ºF with sustained winds of 20 mph..That is when you  begin to see tip damage. The wind which gusted above 55 mph at my house when the temperature was stuck at 13ºF was a little traumatic for me to watch.  Subfreezing wind takes away at least a  full zone of hardiness (10ºF). So i knew that i was seeing the equivalent damage fo 3ºF Zone 7a.

I rarely protect plants from cold. I might bring in a plant or two and for small plants that were just installed, Grevillea, Gardenia, Cistus, I put a cardboard  box over the plants. Small unestablished plants, even very hardy plants including natives can succumb to a severe freeze if they haven’t stretched roots into the ground. I’d add Ceanothus, to the genera that would benefit from this treatment, weight down the box with a rock or a brick and remove immediately when temperatures stay above 32ºF.

Wait to judge a plant- it will probably surprise you