Photo: Source Nasa Earth Observatory – Low-Pressure System over Northwestern Pacific
by David McCloskey
Water in all its forms permeates the region—but where does it come from? And how does it get here?
An endless wave of storms steam in off the Pacific Ocean. A powerful pressure “cell” perched on the crown of the North Pacific Rim generates these storms and much of our weather, dominating the region. Such low-pressure systems form regularly around the Aleutians, then march east and south into the Gulf of Alaska. This brings the famous Northwest Coastal climate of almost constant overcast, drizzle, and copious rain generating thick green forests on the Raincoast.
It all begins with a ripple and a wave…. Warm and cold air slide close to one another along the boundary where two great air-masses embrace and begin to dance across the North Pacific Rim. This boundary called the “Polar Front” is where cold dry dense air down from the arctic meets warm moist more buoyant air-masses up from the mid-Pacific Ocean. (Here is one of the primary paths by which warm equatorial air is exchanged for cold dry arctic air: the earth-sky-ocean system equilbrating itself). The two air masses from opposite directions and places flow in opposite directions–with subarctic air flowing westward and subtropical air flowing eastward. Typically, they flow in parallel but opposing lines, until something disturbs their slip-stream. Just one glance tells you that this coiling, rotating area is power-packed!
The Polar Front flows & swoops smoothly until something disturbs it, throws the flow off-kilter. Smooth lines ripple, and as pressure differences shift, begin to form a wave. Wind shear between the two opposing flows, for instance, may cause a kink in the wave, or even a high mountain top scraping the underside of the sky. A kink in the front leads to formation of a “cell.” They begin their dance coiling ever-closer as they catch hold, in an embrace of opposites, rotating according to Earth’s spin. The rising height of the wave forms where warmer moist air rides up over the colder air-wedge below. The collision between coiling air-masses releases enormous thermal energies. Cyclones formed by waves appear along these fronts–like the Polar Front formed in the cauldron of North Pacific storms. The Aleutian Low-Pressure system is the primary birth-place of Cascadian climate.
Above the Polar Front rides the Polar Jet Stream, marking the boundary between subtropical and subarctic systems. This undulating high river of air sometimes flows as a single huge river, while at other times branching into many swooping streams, as it continually tries to moderate pressure differences. (For the atmosphere is not uniform but highly patchy as well as fluid).
What generates this powerful semi-permanent pressure cell is a process called “cyclogenesis.” Collision of the two air-masses from different regions entangles and entwines them, unfolding one into the other, forming an ever-tightening “knot.” The sub-tropical air streams right as it encounters cold air down from the north, while sub-arctic air streams left as it encounters warm air sliding north. The opposing waves curl and turn back, fold into themselves, braiding together. Turning faster as they capture more energy, their encurvings form a strong inward-turning, ever-tightening, centripetal spiral, becoming almost spring-coiled. Viewed from above, it forms a downward-falling funnel or vortex, the center-axis or “eye” of a developing low-pressure system. The vortex spins like a whirlpool in the sky. This is how the formation of an “extratropical” or “mid-latitude cyclone” works—it depends on sharp temperature differences which are also differences in air pressure, water vapor, etc. This is the movement from “front” to “cell.” A large deep low-pressure spiral is an impressive creation of nature, packed with many “kilotons” of potential energy….
Here in the meeting ground of two opposing air-masses from different atmospheric and oceanic regions realms a new bioregion emerges: the North Pacific Moist Temperate Zone. When these opposites attract, embrace, and intertwine, something new is born. These provide the energies and contours of Cascadia’s climate. This interplay continues year-round, but intensifies in the long cool wet dim season, while waning in the warm dry short season of high latitude summer light (you can watch the interaction unfold on live atmospheric satellite via NASA, NOAA, etc. including the wonderful website “earth-winds” (or null-school.net)).
In sum, Cascadia’s cool wet dim stormy conditions emerge where two different air masses collide. Remember: the cold air forms a wedge as it sinks and dives below the warm air mass, which is then forced up and over the cold air, creating a stacked swirling three-dimensional structure. The rising warm air column becomes turbulent, turbocharged—internally jumbled, rushing madly, instead of smooth lines of flow. Turbulence fueled by temperature differences marks the front—the very active merging, swirling, churning, and tumbling over-turning area between the two air- masses. So they form a turbulent vertical zone of rising and falling air, a kind of vertical waterfall. The rising turbulent air absorbs moisture as water vapor until it hits the “freeze line,” then the vapor-filled cloud condenses and begins to fall as rain or snow. This pressure “cell” spins as the master “cell” of Cascadian Climate….
At the same time, the entangled air masses enter into a counter-clockwise spinning gyre as they wheel across the North Pacific sliding into the corner of the Gulf of Alaska, home of one of the stormiest places on earth. During this phase, the front also becomes entrained in the great northern Polar Jet Stream—that 200 mph river of air roaring 30,000’ above the earth. At Cascadia’s latitude (to 60 degrees), the Jet Stream may touch down to snag the Aleutian Low, helping steer it eastward to our shores…
When storms do approach, they have to “climb the wall” of the ramparts of our great coastal mountains ranges like the Icefield and Boundary Ranges of SE Alaska and northwestern B.C., the massive monolith of the B.C. Coast Ranges, as well as the Cascades and even Klamath-Siskiyous. Sometimes the massive high hard rock wall spins down the storms. But strongly coiled storms slam into the wall, their spinning arms whirling like whips, until flying apart raked by the hard teeth of the mountains. They have to “climb the wall” where the air-masses collide and compress, stacking up like bumper-cars waiting to take their turn over the top. As air cools with elevation, it condenses, wringing out moisture which falls as “orogenic precipitation”—mountain-caused. The mountains stand high as “cloud catchers” with their palms held high to the sky bringing down the rain, running down the western slopes. This is the direct origin of our cascades and “ten thousand” rivers!
Now, Cascadia’s landscape is also laminated east and west by many north/south trending mountain chains, valleys, and interior plateaus. Clouds lofting high above lines of mountains surf down the eastern slopes, drying out as they go. Sometimes there’s a kind of “rotor effect” as the air tumbles down and folds-over within itself, creating turbulence dangerous for small airplanes. It also creates higher pressure. This cascading over & down while drying out creates the semi-arid climate of our interior plateaus (which are not true deserts). Standing on the east side, you can watch the cloud front tumble and cascade, falling down the rainshadow side, then often disintegrating.
This doubled or mirrored cascading on both sides of mountain chains west to east forms the basic dynamic of Cascadian topoclimates—an alternating series of rainsheds & rainshadows. When you pass beyond this regime onto the High Plains, for instance, you know you’ve left Cascadia, entered another world. This special regional regime generates Cascadia’s characteristic flora—great evergreen forests as well as sage grasslands of the wider region.
When the air-masses above and waters below move together, they form what can be called “the Pacific Wave”—the combined winds & storms & waters in tempestuous waves crashing on ragged Pacific shores. These two waves form naturally—any time energy flows in two directions at once, it inscribes a curve, then a spiral on a spinning surface. The streaming of great energies above & below here in this curved world spinning, plus great relief falling down slope, naturally takes a form of cascading. Turbulence is found everywhere, as for instance, in waves and cascades. (Turbulence is another name for Cascadia’s many streamings!) So the turbulent fluid dynamics of the air flows above and the waters below cascade in a kind of great “mirror-play”—a profound resonance. This becomes the template and master theme for energy flows streaming through and animating Cascadia. The Aleutian Low Pressure cell is surely one of the gods of this place…!
These braided and coiled cells of alternating polarities of oncoming high & low-pressure systems throughout seasonal and annual cycles creates much of the dramatic tension of our world here, generates the active motion and rhythm of life. It’s not due to some abstract principles, but rather to converging rhythms of these living energy pulses—which set the “beat” in the score of the song of life here…!
—David McCloskey, Summer Solstice Time, 2025, Cascadia
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