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
And boy howdy did it get cold. This was the coldest stretch of truly arctic air (sub 20ºF) at least since February 2014, and more likely way back in 1990. Probably the most dramatic affect of this outbreak was that it arrived early in the day and sent howling 50-65mph winds across the metro area. More than 350 douglas firs alone came down. This windstorm happened while the coldest arctic air was advecting into our area. So our low temperature on Jan 18, came dramatically in the middle of the day and stayed at that minimum for hours. I watched as my thermometer sank to 13ºF accompanied by snow/sleet and 55 mph winds. These coldest conditions lasted up to 25 hours in several areas near the Gorge. In fact just inside the Gorge at 1,100 on the south side my friend Sue reported many hours with a temperature between 0º-5ºF. Dang.
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
The best way to approach cold damage is to make a thorough examination of the plant. Woody plants will first show tip damage, then leaf damage then stem damage. Stem damage shows up conspicuously as splits in the bark.This can happen up to two weeks after the freeze. burned foliage and the first stage of damage can also wait at least two weeks after the thaw to become apparent. The next stage of discovery is after the first day in the 70’s- the plant will have fully broken dormancy. This is especially important for deciduous plants and perennials. Also, for sub shrubs like Fuchsias, Abutilon, and Sallvias its important that you wait until all danger of frost has past to cut them back. Most shrubs with black leaves will lose their leaves and regain new foliage very quickly. Make sure that any plant that was damaged gets extra water, love, and mulch the following summer. This will speed recovery. Its amazing the rejuvenating power of water.
We’ll be opening the shop in early February. Stay tuned.