El Nino/ENSO here we go.

El Nino- Southern Oscillation

El Nino is one of those terms that gets slung around the press and I’ve found that referring to it in sound bites and quips doesn’t explain it and just leads to more confusion. When a prominent meteorologist at NASA recently predicted a “Godzilla” El Nino- that didn’t really help.  Part of that misunderstanding is inherent in its vague cyclical nature. It doesn’t occur every year like winter- its not as reliable as our change of seasons. I’m going to attempt to explain it in the least vague way possible. Cut through all the bullshit and get to brass tacks. Bear with me as I do a little explaining. And yes, it has a direct influence on our gardens in the PNW.

Hot child- Reversal of winds

The origin of the word Monsoon is Hindi. It doesn’t mean rain- it means a reversal of winds. On the Indian subcontinent that means that following the furnace that is offshore winds in April to June the intertropical convergence zone shifts north- onshore winds that herald rains and an end to the scorching weather.The intertropical convergence zone is a permanent weather feature approximately 20º north of the Equator where a worldwide band of rising air creates precipitation- both north and south of the equator. As the earth tilts on its axis and seasons commence this zone moves north or south. The (ITCZ) shift is as reliable as seasons.  A reversal of winds. Remember that because it is not too terribly different than the origin of El Nino.This is predictable and expected almost 100%. What, however, if this reversal of winds was not as reliable as clockwork? Not only does it throw a wrench in forecasts, it affects the whole world and because of its less predictable occurrence we have less of its effects to identify with. Humans like certainty- nature is messy though and we have to acknowledge that to begin to understand El Nino.

What goes east now goes west

The cause of El Nino which is most commonly referred to as EL Nino/Southern Oscillation or ENSO is not fully understood, but its recurring pattern is very well documented.   First- El Nino is so named because its most dramatic effects show up in December in the eastern Pacific just off the coast of Peru/Equador  primarily around Christmas- hence the name El Nino or the (christ) child.  In the equatorial Pacific winds normally blow east to west. This does two things. It forces sun heated surface waters to the west towards SE Asia and N. Australia. In the eastern Pacific this displaces the warm surface water and cold water rises this is called upwelling. Cold water holds more oxygen and this supports much more marine life. Fishing is good. In an El Nino year warm oxygen starved water  pools towards that continent – warm water holds less oxygen and it deters marine life- fishing sucks.  For an unknown reason every two to seven years (5 years) this wind reverses its flow. Under normal conditions the persistent east to west flow moves the warm surface waters towards the west. In an ENSO event the opposite is true, because of this the entire Pacific basin reacts in various (almost) predictable ways.

Warmer to the North and Cooler to the south- the ultimate reversal.

Several things that are predictable happen in an ENSO event. But no two are completely alike. Just as no two winters are completely alike. In the Pacific basin there is a common effect and it has a profound influence on our winter weather. To begin, warm water has more latent energy and that means the air above it holds more moisture. In northern South America that spells rain for normally parched coastal Peru and Equador. In fact, the southern branch of the jet stream- the subtropical jet becomes energized. This has two effects. This southern branch pulls energy from the normally much more vigorous polar jet to the north (thats what soars over us). This energized jet sets its sights on California and actually all the way across the southern tier of North America. Volatile, soaking storms move in south of us- California can receive a drenching winter. Across northern Mexcio and the southern US precipitation increases and this blocks out sun energy- its cooler there than typical climate averages. At our latitude the paltry polar jet dwindles. Most often a semi-permanent ridge of high pressure sets up off the PNW coast and the weakened storms are split and disintegrate as they are steered inland. The whole Pacific basin is warmer as well so the effects for us are drier, warmer and pretty much bland winter weather. This stretches across the northern tier of the US. The normal mixing and fast motion of the polar jet is perturbed and warm air drifts to the north- all the way in fact to the poles. Check out this winter forecast from the NOAA. It calls for a classic El Nino winter set up. Orange is above normal temperatures and blue is of course colder than normal.

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What are the effects?

Warmer drier winters are detrimental to our snow pack. If you are a snow boarder or even if you irrigate in summer this affects you. Less mountain snow pack is less water in our collective water bank for summer. If you are a gardener and you think this means a zone 9 winter and the coast is clear, think again. In approximately 80% of our ENSO winters there is no arctic event. As I said though, like seasons no two El Ninos are alike. We look at the past in climatology to tell us what the future holds. The last ENSO that was as strong as the one we are facing was in the winter of 1997/98. We DID have a short arctic outbreak in that winter so that represents the 20%. Remember that it only takes a few days to produce enough plunging cold effects to mangle tender plants. So while it is not a sure thing that we won’t see arctic conditions 80% are good odds. As for our ‘drought’- which I don’t personally consider it a drought unless rainfall is down for two years in a row, it doesn’t look like the NOAA has high hopes for a typical liquid winter. (See below- brown is drier and green is wetter).

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Click on individual map to view larger format

A few other facts

As I said ENSO changes the weather all over the globe. For instance one effect is that the energized sub tropical jet that flows over the southern part of our continent and into the Atlantic basin causes upper level wind shear that makes it hard for Hurricanes to form there. The warmer water off the coast of western Mexico actually increases the formation of tropical systems in the eastern Pacific.  Far away in Australia and SE Asia cooler waters and stagnant wind flow creates dry conditions. This can be monumental and one knock off effect is drought and higher fire danger. During the last strong ENSO fires scorched huge sections of Indonesia and this loads the atmosphere with carbon- not good for climate change. Its important to note that ENSO events have become not only more frequent in the last 50 years but they have become stronger. Is this a product of climate change? Only the future will answer that question.

-Paul

El Nino/ENSO here we go.

My favorite Microclimates. Know your garden and grow kick ass plants.

Admit it- Zone Envy

We all want to grow things that stretch the boundaries of our climate. Maybe just a little bit. If you ever want to meet an intense group in this realm hardy palm people are the best. They dare to grow a Trachycarpus in Zone 6 Pennsylvania- and damn they make it work. You can, and I have learned a lot from this group of intrepid gardeners. But understanding microclimates doesn’t  just mean you can get away with something (and isn’t that the root of zone envy?) It makes us better gardeners. Without going into thermal diagrams and intricate wind flow patterns I would like to share my observations about some of my favorite ways of using microclimates to your advantage.

#1 The top of a slope

Cold air sinks. Don’t get all hot and bothered over your elevation. Being on the top of a hill in the Willamette Valley has serious benefits. And- I am not talking about huge mountain sides. Even small slopes create microclimates.  These are called thermal belts. At our wholesale nursery there is a 10′ slope with a 45º grade. Just for shits and giggles I planted  two of the same species of semi-hardy Grevilleas one at the top and one at the bottom. In December 2009 we plunged to 7ºF out there. And sure as shit the Grevillea at the top of the slope was UNDAMAGED and at the bottom? You guessed it. Dead as a door nail.  Locate the highest part of your garden and then imagine cold air flowing like water down the slope because cold air is dense and heavy- it hugs the ground and it does flow like a liquid. Houses, fences, even hedges can interrupt this flow and there cold air collects. And as I have said, even small slopes have their benefits. If your garden is flat as a pancake, don’t worry- there are other microclimates that exist on the flat plane.

1000 year old stone walls

Yeah- those are in short supply in good ol Oregon but walls do have their benefits. And they have their drawbacks. Primarily south facing walls collect heat- even on seriously subfreezing days- solar wave lengths are amplified there and they can then radiate some of that heat back. This is good and bad. In my experience plants that require heat to harden off their wood for winter cold are ideally located here. A perfect example is Caesalpinia gillesii. It prefers summertime heat to harden off its woody structure which makes it hardier to ultimate cold in the winter. In spring and summer the reflected heat of a wall spurs it into bloom earlier and longer. A win win. And it goes safely and very dormant in winter. A lose lose however, is when this heat works against you. I’ve placed tender broad leaved evergreens against south facing walls in hopes of garnering added protection. Nope. What happens is that the reflected heat actually interferes with dormancy and then when a real arctic plunge sweeps in they have not hardened off adequately to withstand our lowest temperatures. For many borderline hardy plants, believe it or not- and I say believe it- full exposure is the best site. This lets frosts do their magic of inducing dormancy. And as a gardener I have come to respect the power of dormancy. You can call me a heretic, but I’ve tested and observed this for 25 years and it works. Of course even in this situation a plants ultimate tenderness to cold can be exceeded and it can be lost. But there are other microclimates you can seek for protection that do work miracles.

Get to know your sidewalks and asphalt.

Some of my most successful placement of semi-hardy plants has been adjacent to concrete sidewalks and the asphalt of the streets. Several things combine to make this a win win win. First the plant is in the open- preferably (but not exclusively- I’ll come back to that), that means it receives the full measure of dormancy. Then radiative heat from the hard surfaces raises the temperatures just a little- notice how snow melts first on black surfaces that collect heat as well as sidewalks? Thats heat working in your favor. The most surprising trait of this location is that roots are drawn under the paving – because it is perpetually moist from shading. Pavement is a great insulator and this protects the roots from freezing as well as not interrupting evapotranspiration (moisture loss that can desiccate a plant) during a freeze event. Even brick pavers and large rocks can create this effect. Its important to note that most of the days of our freeze events occur with clear sunny weather. And even long wave radiation from the weak winter sun can penetrate cloud cover and contribute to the ambient heat of paved surfaces. So- in the open the plant is exposed to dormancy inducing frosts but during arctic episodes the reflected latent heat of the pavement boosts the temperature. It works great. Some plants that I’ve grown successfully in this situation are: Woody Salvias, such as Salvia greggii and hybrids, Grevilleas, (which love this situation), Callistemons, Agaves and even (in a semi shady location) Gardenias- I had a tender cultivar live 10 years undamaged with its roots below pavers. Play around with this and see what you think.

South facing aspect

Lets face it we are far to the north. Almost exactly half way to the Arctic Circle in fact. The sun angle is low in winter but on south facing slopes the maximum amount of solar insolation   means that these situations can be a few precious degrees warmer. Located on a slope- or near asphalt and the the two previous micro microclimate benefits can double up. Spend time in your garden in winter- outside during the coldest episodes. Notice where the ground thaws first, where snow disappears first, where soil remains frozen and frost lingers. These simple observations are eye opening. I can tie into this location the benefits of overhead protection. Tree branches- especially evergreens- but to some extent even deciduous branches interrupt heat escaping on our coldest nights. When the canopy is high enough- you have two effects. It still gets cold enough to induce dormancy but long wave radiation escape (heat loss) is interrupted by the branches and it adds a respectable amount of protection. Located on the south side of a tree canopy plants that are tender can sail through with minimal damage. Just remember the phrase woodlands are warmer.  This goes for the overhead protection of porches and even eaves. So as a gardener while you spend a lot of time staring down at the dirt it is equally as important to look up as well. One plant that really benefits from siting in this situation is Edgeworthia- which as gardeners know can have flower buds frozen in early or late freezes. Overhead protection really works to minimize damage.

Your own personal Ice Box

The opposite of a southern aspect is called an open north exposure. The north side of a house, a hedge, an unwelcome 6 story building can cause shade. There frost and freezing temperatures linger. The soil can become more and more frozen- and the low sun angle means that there is little if any thawing. This situation can create up to a half a zone colder conditions. Locate hardy plants here- perennials, really tough shrubs- in the summer this is a great site for Hostas, Hydrangeas and Rhododendrons.

That god forsaken East Wind.

Our arctic episodes come to us in two ways directly from the north and in the Portland Metro area from the east. Arctic air collects east of the Cascades and is funneled- and as you know quite violently through the Columbia River Gorge. (This is called a Bora wind). Portland is on the direct receiving end of that pressure gradient. So its important to locate plants that can be damaged by the intensely cold and extremely dry arctic blast. Notably, broad leaved evergreens- (New Zealand Pittosporums come to mind) I’ve tried to cover many plants with Remay, sheets, even Scooby Doo sleeping bags to protect them from this wind. To be honest the Remay and sheets simply blow away in the gale- no matter how hard you fasten them. (Scooby Doo sleeping bags simply crush the plant). So, in this case its location, location, location. A western wall or west side of a hedge interrupts the main focus of a gale. And be aware that these winds are sneaky. They swirl around and between houses, fences and hedges creating eddies- pay close attention during our next East Wind Episode and you’ll see what I mean. So a west facing wall works well but also, I’ve found locating tender plants in the midst of cold hardier shrubs offers very good protection from wind as well. Its all about the mix and the protection of friends. They can keep the full force of the wind from frying your plant. This works amazingly well with such plants as Abutilons, Drimys, Phormiums even semi-hardy Scheffleras.

Snow cover

As long as we are discussing cold its important to understand what snow cover does. It can be good and it can be VERY bad. You may have heard that snow insulates plants from cold. Yes, and no. 1′ of snow has some insulating power. 2″ (which is what we are likely to get) offers little protection. In fact it can be very bad. Just an inch of snow can excel the long wave escape of heat from the surface that means that our temperatures with just a skiff of snow can be MUCH MUCH colder when its in place.  So, if you are praying for snow to protect your plants- think twice, just a little can cause over night lows to plummet with no real benefit and real risk. If a plant is covered with snow- do not remove it. Unless branches are breaking- then god help us all- Snow on leaves interrupts moisture loss and its kind of pretty too.

Keep it simple

I hope I have offered some suggestions that will make you as a gardener aware of your microclimates. It pays to play around with it and experiment. Keep your eyes open and really pay attention to weather as it happens. This is not just for tender plants but also for most others. Get to know the weather in your garden. And grow kick ass plants.

Paul

My favorite Microclimates. Know your garden and grow kick ass plants.

Climate Change, Speedy Gonzalez, and the Lazy Jet Stream

There is a theory that you will be hearing a lot more on weather forecasts and climate change discussions. This is a gardening blog first and a weather blog second- the idea is to tie the two together. They go hand in hand. The more you garden the closer you watch the weather. In our mostly benign climate we like to grow as much as possible. That means the two overlap. Zonal denial made famous in our region in the last 15 years couldn’t be a more perfect example. The term you will be hearing is ‘The Lazy Jet Stream’- as opposed to the lazy gardener. Of which I am guilty.

Jet Stream 101

To understand how weather works you need (especially at our latitude) to understand the Jet Stream- what it is and what it does and a few facts about it that I will try to explain with as little scientific hoo haw as possible.  The jet stream is a river of air that moves from the west to the east at our latitude and is responsible for virtually all of our weather. This is called the polar jet. It is formed because there is a temperature gradient that occurs world wide from the cold poles to the equatorial tropics. Cold air from the arctic does not stay in place, instead it migrates south. The same is true of tropical air- it migrates north. Where these air masses commonly collide is at the half way point (to be broad) which is us at just north of 45ºN in latitude- Hello Portland! This collision causes the jet stream and in concert with the rotation of the earth a river of wind in the upper atmosphere that moves rapidly from west to east. The jet stream is associated with (frontogenisis) the formation of storms and fronts (the boundary and movement of two air masses).  Essentially, on the north side of the jet stream is colder air- which is more often associated with rain and snow- air from the poles. On the south side of the jet stream is ridging- most often associated with warm and dry conditions- air from the lower latitudes.

Zonal, Ridge/Trough- Speedy Gonzalez

The jet stream varies greatly in its strength depending upon the season. In winter there is a much greater temperature gradient between the arctic and the tropics. This energizes the jet and as I mentioned this creates storms and our famous rainy season. As you know in winter this can mean storms plow through every few days like Speedy Gonzalez. The jet stream is directly over us or slightly to our north or south. Its that steep pressure gradient that keeps things cruising along. When the flow is directly west to east (a horizontal line) its called zonal. But weather is anything but constant and the speed of the jet transverses high pressure ridges and low pressure ridges like a windy road. As the jet stream speeds up the acceleration/deceleration of the air flow induces areas of low/high pressure respectively, -we get a parade of ridges and troughs.  This is called ridge and trough.  Troughs dip down from the north and ridges impinge from the south.  So, there is zonal flow- directly west to east and ridge/trough- high amplitude waves north to south in the Jetstream. In the summer when the temperature gradient from the warming poles of the north to the equatorial south is much less the jet stream decreases in velocity and the parade of storms and troughs becomes sluggish to non-existent- ridging takes hold.  Our annual dry season. Well, what if the temperature gradient that fuels the speed of the jet stream was shall we say perturbed?

OMG did we kill Speedy?

We may actually be seeing what happens right before our very eyes. The theory- which makes a lot of sense is that because the poles are warming more rapidly than the lower latitudes the pressure gradient whose intensity speeds the jet stream along may be waning. A lazy jet stream. What is the big deal you ask? Well, when we hobble Speedy Gonzalas the jet stream begins to slow down and that has big implications. Instead of weather systems such as ridges and troughs moving steadily and quickly- and for instance the weather pattern moving as well- we get a slowdown in pattern changes. Weather conditions become more static and that can cause some real problems. If you are in a wet trough pattern- then you stay there not just for days- like we expect but for weeks- possibly months. If its raining, it will keep raining- this can obviously lead to flooding.  If its hot under a ridge of high pressure then the stagnant conditions remain and heat intensifies.This can lead to flash droughts or long term droughts. This explains why weather events are not just strong- and they have always been, but now are persisting. This looks like a trend.

Typical heat waves are in and out of here.

One example of this- and believe me meteorologists took notice was our weather this past hottest June of all. Oregon has always had heat waves and they can be pretty intense as we well know. But there is a pattern and set up to these heat waves that naturally limits their length of time – a healthy Jet Stream, but not necessarily their intensity. A typical heat wave for us begins with a ridge of high pressure nosing north to cover our region (ridging). It moves north up the coast and atmospheric heating- warm air rising at the surface causes a heat low which is oriented as a north south trough located off the coast. The air from inland regions is pulled off the coast the first day down the mountains drying and heating as it goes. This can cause temperatures at the normally cool coast to soar- but then it is short lived. The second day the heat low moves east and orients itself north to south over the valleys of western Oregon. The coast cools off rapidly as the flow turns onshore. Hot air from south and east of the Cascades is drawn directly into the valley heating and drying as it goes. Inland, this is our second day of a typical heatwave and its often the hottest. The third day day the heat low moves over the Cascades and east of the crest they begin to heat up and our temperatures in the valley drop slowly at first then cool marine air rushes in and the heat wave is over. This is a pattern that repeats (in various intensities) a half dozen times a summer- and this is with a much less powerful jet stream that is primarily to our north in the warm season. Our most recent heat wave when we peaked at 103ºF and higher was a closer example of a typical heat wave. A few days in the 90’s to a day or two in the 100’s and then back down to seasonal averages. This is how we usually accumulate our 14 average days above 90 and one day a year of 100. I’ve watched this pattern my whole geek life.

But June? Why was June and the beginning of July so hot?

The difference in the heat we experienced for most of June into the beginning of July may be a local example of a Lazy Jet Stream. Instead of a fast forming and mobile heat wave  this one stuck around. A persistent ridge which had no intention of moving on. And this pattern is being repeated all over the globe in different ways- aside from the typical press hyperbole its important to listen to the details of events. For instance just how long did that monsoonal rain in Myanmar fall? How long was the heatwave in the Middle East roasting those poor people? (Two recent events of note). And this could be happening and will on a more macro scale. The drought in California is associated with a persistent ridge of high pressure that is not just stagnant- it weakens for a bit and then bam! It reforms. The Eastern part of the country has had two winters where they were stuck on the wrong side of the Jet Stream. (Remember the Polar Vortex?) and intrusions of cold air one after another dove south. Eventually, leading to all time record snowfall in Boston among other places. Meanwhile we on the west coast basked in a persistent ridge for most of winter and spring. Our June heat which was so notable for its length and not necessarily intensity, PDX  only got as high as 97ºF but there was a nearly uninterrupted string of 90ºF plus for almost two weeks- including the warmest over night lows ever for June. Could this be a view into our future?

Pay attention

I’m not saying that our local weather is going to change completely. And you should always have facts to back up any claims. What is most important is to pay attention to trends and events. Global Warming is a grand and scary experiment and as far as I can tell people are learning more and more as it intensifies. And, there is a reason so many long standing records have been broken in the 21st century. Could it be that we’ve broken Speedy Gonzalez?

Climate Change, Speedy Gonzalez, and the Lazy Jet Stream