Tag: Snow

Here Today, Gone Tomorrow

Ah, snow— tiny frozen ice crystals falling from the sky.  Snow is amazing— chillingly beautiful and fun to play in. Great for skiing, snowshoeing, sledding, and don’t forget building snowmen.  But most of the world’s snow is ephemeral. It is like a holiday, or romantic tryst—magical at the moment but doesn’t last.  

However, it is the ephemeral nature of snow that perhaps makes it so vital.  The fact that snow hangs out for a while on the landscape is one of the most important features of snow. How snow accumulates, shifts and changes form, and eventually melts away, significantly influences the ecology, hydrology, and natural resources of the land. 

Change

While snow is a great influencer, it is also greatly influenced. From its start as a snowflake falling from the sky, its fate depends on a host of environmental factors. Just a little nudge in temperature, or a small shift in humidity, and snow will change. It may fall as sleet, or turn into rain. It may not accumulate or melt early.

Concerns around changing snow, brought me to reach out to Christina Aragon, snow hydrologist and Ph.D. student at Oregon State University. After seeing her speak at a TapTalk in early February 2020, I HAD to see if she would be up for a snowshoe with me. She agreed. And before the month was up, we headed into the Cascade Mountains to find some snow.  

The Hike

Special as a Snowflake 

We arrived at the Potato Hill Sno-park late in the morning.  The snow was falling as we strapped into our gear. It was still falling as Christina and I began our steep ascent through the white and drifted snow.  

We had gone no more than a few 100 yards when Christina wistfully reached out and caught a few snowflakes on her glove. I leaned in closer to have a look. Christina explained as I tried to make the details in the tiny crystals on her glove that, though each snowflake is unique, snowflakes can be classified by their shape.

Different snowflake shapes will form depending on the temperature and relative humidity in the atmosphere. The snowflakes that were falling while we headed up potato hill were mostly clusters of needles.  Needles, which look a lot like their namesake, form when the temperature is relatively warmer and humidity is at mid-range.  

Christina also caught a stellar dendrite in flight, but it quickly melted into her glove. 

Stellar dendrites look more like a classic snowflake- flat with six intricate lace arms coming out from a center.  Stellar dendrites will form when humidity is higher and temperatures are a bit warmer, or if the humidity is really high, but temperatures are cold.  (They also form when you combine a six-year-old with a white piece of paper and scissors, but I digress.)

Several different snowflakes can fall at one time, but usually, one type predominates.

Other snowflake shapes include columns, capped columns, and six-sided plates.

Also, keep in mind snowflakes are small, defined as a single crystal.  If you are looking out the window at what appear to be large fluffy snowflakes, these are actually clumps of snowflakes falling together. This occurs when flakes fall and start to warm up, melting into each other.  

What’s the Graupel?

Not all ice falling from the sky is snow or made up of snowflakes.

Graupel is another form of falling ice crystals.  Graupel forms when a falling snowflake collects supercooled water droplets on its surface forming a large (2-5 cm) rounded pellet.  Though not a snowflake, graupel is a type of snow.

In contrast, sleet is not snow because, though it may start as snow, it melts and refreezes into ice.

Who knew that just defining snow would be so complicated? 

A slice of snow cake

Up the tree-lined road, we continued walking along what felt to me like very stable snow.

Just a couple of weeks ago, I had been snowshoeing through snow that was very unstable. That got me wondering—Why was that? What happens to snow once it reaches the ground? Why was the snow today such a pleasure to walk on compared to before? I asked Christina for the skinny on-ground snow. 

Once the snow falls to the ground, like a caterpillar in a chrysalis, it begins to undergo metamorphosis (though the change is less predictable than you get with a monarch). The best way to see these changes is to dig in and look at the layers.

Digging a snow pit reveals a snow profile.  A snow profile serves as a record of events in the “life history” of the snowpack. It can also help you determine its stage of metamorphosis—is it becoming more or less stable, for example? So that is what we did.

Our snow profile revealed fairly stable snowpack conditions.  By running a finger or two through, and into, the snow layers, we were able to identify a softer “new snow layer” and a deeper layer of very “stable rounds”. 

Rounds or Facets

New snow layers still retain some of their original crystalline shapes and are less dense. While deeper in the snow, either rounds or facets will form depending on the temperature gradient.

Rounds form in snowpack when the temperature range through the snow is pretty similar throughout the snowpack, or isothermal.  When the temperature gradient has more than a 1 ° C change for every 10 cm of the snowpack, this is a sign that facets are forming.

Facets are unstable and can lead to avalanche danger. Unlike rounds that have sinters that hold the snow together, facets are large and angular with points and don’t stick together well. Imagine “sticking your finger into sugar” and that is kind of like what facets feel like, explained Christina.

Rain Crusts

In addition to the two main layers, our finger test revealed a small rain crust in our snow profile. Rain on snow is a source of latent energy, as the liquid water freezes on the snow, energy is released into the snowpack.

A rain crust can also change the movement of water through the snow. Instead of water flowing vertically through the snowpack and into the soil below, water can flow horizontally through the snowpack along the ice layer.

One of these Snow is not like the Others

In the Cascade Mountains, having a stable snowpack is actually the norm compared to other places in the U.S. Snowpacks in maritime snow climates, like the Oregon Cascades, generally form right at freezing temperatures, building deep, dense, wet snowpacks. In continental mountain ranges, like the Rockies, temperatures are much colder, and the air is much drier creating a shallow, less dense snowpack. Think fluffy “champagne powder.”

The maritime climate of Oregon’s Cascades results, not only in relatively warmer, but much deeper and denser snowpack. Warm moist air is carried inland from the west, sometimes on huge atmospheric rivers, and pushed up over the Cascade Mountains- this is called orographic lift.  The result is that as this air rises, it cools, and the moisture is squeezed out as rain or snow.  

Losing Structure

The unstable snowpack I experienced a few weeks ago, was probably due to a loss of structure that can occur with mid-season melt (another very Oregonian snow predicament). In this case, mid-season melt probably caused most of the sinters that hold the rounded snow together to melt away. The remaining snow was more like a loose collection of rounded pebbles of ice with very little strength.

Snow on Fire

Nearing the top of Potato Hill, the scenery changed from snow-covered trees to more open terrain. The B&B Complex fire of 2003 burnt down much of the forest in this area.  

Observing snow in burnt forest areas, was one of the ways Christina first became interested in studying snow.  In B.C., when one of her favorite forested snow recreation areas was burnt, she noticed that the snowpack was gone MUCH earlier than before the fire. Christina was later able to work with Dr. Kelly Gleason on a research project that explained the phenomenon.  

Black Snow

We hiked up to one of the burnt trees on Potato Hill where Christina pointed out its charred bark. She explained how black carbon and micro-charcoal particles from trees and other sources end up in the snow following a burn. 

Snow normally is very reflective of the sun’s rays—it has a high albedo. However, as dark particles accumulate on snow’s reflective surface, instead of bouncing back, the rays get absorbed by the black carbon, heating up and melting the snow!  

We dug into the snow to see if we could see the particulates in the snow on Potato Hill.  Despite the fire being over 10 years ago, the snow still looked dirty with particulates. 

More Melt

However, black snow is only one factor that affects snowmelt in the west. Climate change is causing shifts in both the quantity and timing of snowfall in the western United States. Many places in the west are already seeing a decline in snowpack and a shift to earlier spring snowmelt, trends that are expected to continue.

This is a huge problem! Snow is a reservoir for our water supply—storing water for later in the year when we need it.  In the western U.S., about 70% of our runoff originates with snow. With the timing of snowmelt shifting to earlier in the year, runoff is making it into our valleys too soon, and we don’t have the supply we need for later in the year. 

A Vicious Cycle

Less snow means less reflection of light from the sun (lower albedo), which means more heat absorption and more melting—a vicious cycle.

Earlier melting of snow also results in dryer forest soil in the summer and a longer fire season, which means more black snow and more melting. Another vicious cycle.  To make matters worse, the effects of black carbon on snow are not short-lived either—lasting 10 years or more. 

Snow Measurement

Pelted by crystalline water droplets, Christina and I reached a “viewpoint.”  Here we stopped to celebrate with pictures and a snow depth measurement.  

A big part of Christina’s Ph.D. work involves improving models of snow distribution in mountainous and remote places in order to better understand water resource availability during the year.  In order to do this work, good reliable snow data is needed. In particular, she needs to know the SWE of snow. SWE is snow water equivalent, the amount of water contained in the snowpack, and is based on snow depth x snow density.  

Measuring SWE is not easy to do and involves heavy equipment that most people don’t want to carry in their packs.  So instead of measuring SWE, Christina encourages and promotes a citizen science project called Community Snow Observations.  Data gathered by the project is used to validate data gathered remotely and improve snow models. And the best part is it is easy.  Using an avalanche probe, or even a ruler, you take several depth measurements, average them, and then report the value using an app. 

Become a Citizen Scientist

Finding SWE from depth using both ground and remote sensing technologies is a hot area of research in the hydrology world.  It is also research anyone can get involved in. If you want to do your part visit communitysnowobs.org to learn more. 

 Shifting Snow

On our way back down the hill to the car, Christina and I talked more about what to look for when in a snowpack environment.  

The distribution and build-up of snow on the ground are always in flux, which can make it both extremely interesting to explore, as well as very complex and hazardous.  Here are a few variables to consider while hiking in the snow. 

Number 1- Trees. 

The effects of trees on snowpack are complicated.

Trees can intercept snow, preventing it from reaching the ground where it accumulates, and increasing rates of sublimation, the direct transition of snow to water vapor. When branches of a tree are wide with low hanging branches, like most conifers this can also result in the formation of dangerous tree wells.

Trees also emit longwave radiation, like other dark objects, making the snow around trees slightly warmer than open areas, which may lead to more melting, particularly at the tree’s base. However, at the same time, forests block a lot of incoming solar radiation from reaching the forest floor, slowing down snowmelt in many forests.

Number 2- Wind. 

The wind moves snow around a lot.  Where the wind is going and coming from changes the profile of the snowpack—making it more shallow in some areas, and in others really deep and hazardous.  Wind loaded slopes are a real avalanche danger that can occur on downward slopes where wind piles up snow. Wind scoured slopes, like the top of a peak, will have a shallow profile and can be difficult to travel on. 

Number 3- Elevation

In general, the higher up you are in elevation the more snow will accumulate (with the exception of peaks scoured by high winds).  Snow profiles deepen at high elevations and may present more layers. Thus, to understand the snowpack in an area, it is generally a good idea to dig snow pits at multiple elevations and locations. 

Number 4- Aspect.

North-facing slopes receive less solar radiation than south-facing slopes.  Even on a small scale, once the snowpack enters the ablation period, where it is melting off, south-slopes will melt off faster.  

Number 5- Slope Angle.

One of the easiest factors to keep in mind when considering potential hazards in a snowpack area is the terrain.  Steeper slopes are much more prone to avalanches. If your slope is between 20-25 degrees or less, your risk of avalanches drops significantly. 

Let it Snow

Phew!  That was a veritable blizzard of snow information!  So don’t let it melt away. Instead, hit the snowshoe trail, catch some snowflakes, dig a snow pit or two, measure the snow, or simply watch the snowfall. And next time you take a shower or sip your favorite beverage, think about those cool white flakes. Because odds are, that liquid you are enjoying, first fell as snow! 

Christina Aragon is a Ph.D. student at Oregon State University studying hydraulic modeling.  Originally from Denver, Colorado, she has experience in avalanche operations and snowboarding.  She got her undergraduate from the University of British Columbia where she studied kinesiology and ecology. She got her master’s in Geography from Portland State University where she studied hydro-climatology.