FORECASTING SKI CONDITIONS PART II

I’m often asked:  "Howcum some people know where to find the best snow, where to go first to get the blower pow, and which skis to pull out on a given day?"

 

If you haven’t yet, read Part I (here) for details about how & why our weather data is generated, and THIS at skicrystal.com!

 

OK, look at the following example taken from the telemetry data (red letters added by me) gathered by the Northwest Weather and Avalanche Center.   (But first, take a moment to join Friends of the NWAC to support all they do to help keep winter recreationalists and mountain pass drivers alive!)    

 

WATER AMOUNTS

Snow falls in a little bucket that’s kept just barely above freezing by a little light bulb that keeps water in its liquid state without evaporating any of it. This is done so we can measure the amount of water in the snow, because regardless of snow density, we know the weight of water, right?  (Remember that little mnemonic device– “A pint a pound the world around”?) 

 If you’re like most people, you probably don’t care much about the weight of the snow upon which you shred, but it’s one of the factors used in forecasting avalanche danger, which is why we collect all this weather data..

Each row is for the particular hour indicated in Column A.  Look across at Column E and you’ll see how many “inches of water” fell–as either water or snow depending on the temperature outside.  The temperature is indicated by 2 Columns B (base area weather measured at 4480 ft. & Summit weather measured at 6870 ft. 

If the temperature is 39° F (4°for you Canadians and other scientific-types) we know that water all fell as rain! Density = 100%. Good for bathing, not that good for skiing!

If the temperature is -10° C (14°F) we know the snow fell as cold smoke, about 5% density. Soft new snow at the upper elevations of Crystal Mountain is typically in the 10-12% range. And as sort of a general rule of thumb we say that typically an inch of water = 10" – 12" of snow, or, that every 1/10" of water = about an inch of snow.

So if you compare the Base & Summit temperatures, you can estimate the approximate density and amount of new snow at whatever elevation you plan on skiing. Keep in mind that sometimes temperatures are "inverted" and it’s warmer higher up and colder down low.  (I know, CRAZY, isn’t it?)

 

OK, now let’s look at the THE WIND

In Column D:

· 0° and 360° mean the wind is blowing FROM the North, toward the South.
· 90° = blowing from the East toward the West,
· 180° = from the South toward the North, and
· 270° = from the West toward the East

The harder the wind blows (Column C) the more it picks up the snow from the “windward” side of mountain ridges and deposits it on the "leeward" side.  5-10 mph means we only get a little of what we call “snow transport”. (Sorry rest-of-the-world:  my USA-born, humanities-educated little brain is too puny to convert kilometers-per-hour, but there’s a snazzy chart to do so here.)

20-25 mph winds mean significant amounts of snow accumulates downwind, especially as it gets colder and the snow gets lighter and fluffier. Ridges themselves BlOCK the wind, which slows it down considerably, forcing it to drop all that snow it was lugging around. On the west slopes of the central cascades the prevailing weather pattern causes the wind to blow Southwest-ish (from the South, Southwest & West) depositing snow on Northeast-ish (North, Northeast, & East) facing slopes, most of the time.

Typically, in our area, winds above about 35 mph will tend to STRIP the snow from the windward side of slopes and deposit it leeward, so snow accumulation can change even if there’s no precipitation! 

(I’m gonna repeat that for the hot-shots who whine when the telemetry shows a snow depth increase when there hasn’t been any precip:  SNOW ACCUMULATION CAN INCREASE–in certain areas–EVEN WHEN IT HASN’T BEEN SNOWING!!!  O.M.G. People!   O–M–G !!!)

So if you see bare rock on the windward side of a ridge, you might expect much deeper snow–or at least deep pillows & pockets–on the leeward side!  If the wind is blowing sideways to the slope, you may get dynamics of both accumulation and wind-packing.  (Cold temp. wind-packing can create chalky "hero-snow" conditions.  Warmer wind-packing can create scary "trap crusts"–firm on top, soft underneath–that make your skis and boots want to go in a different direction from the rest of your body! )

 

OK, that’s the wind. Now how about THE SUN?

The sun can melts snow crystals. (Raise your hand if you already knew that!)  But North-facing aspects tend to remain in shadows, so they tend to stay lighter and less sun-affected, remaining either fluffier or chalkier depending on whether or not it was windy when the snow fell. That’s why Crystal is such a great ski area–it’s a succession of North-facing bowls. From the South (far left in the photo below), ya have yer Three-way Peak, yer Silver King, then The Throne, Silver Queen (Powder Bowl), Green Valley, Snorting Elk, Northway/Bruce’s/Paradise, & Morning Glory.
 

 (If you’re not familiar with Crystal Mountain, everything shown here is part of the ski area, with several hundred acres not visible to the right of this photo.)

 

SNOW SETTLEMENT

The snowpack also settles over time and becomes denser. Try this: go buy a few boxes of Lucky Charms and tell a kid to eat everything but the stars. (But not in one sitting cuz that’s just cruel.)

Then take those left-over stars and put ’em in a coffee can. (As if anyone in the Northwest still buys coffee in a can, huh?)  Shake it up and you’ll notice that your starpack becomes more dense from the air getting pushed out as the pointy parts of some stars fill in the crotchy parts of adjacent stars.
 

Settling can be caused by

  • Wind,
  • The Sun’s radiation,
  • Compaction caused by grooming machines, skiers & boarders,
  • Overnight “drying”, which is actually called "faceting".

Have you ever heard people say “the snow dried out overnight” on a cold morning when the air sparkles like pixie dust and the snow surface looks like it’s full of diamonds? What they’re describing is actually a process where large temperature differences within the snowpack (because a clear sky is so cold at night, but the ground stays fairly insulated under the snow ) causes water molecules to transfer from the pointy parts of snowcrystals into the crotchy parts.  So instead of the crystals looking "fingery" (left photo) and locking together like those Lucky Charms, they’re more hectagonal (right photo) and feel like skiing in sugar.  That is–until the sun hits ’em and warms ’em up! 

  

 

SO THEN, combining all these things…

  • Water amount,
  • Temperature,
  • Wind speed,
  • Wind direction, 
  • Sunshine intensity,
  • Cloud cover & shade
  • Directional aspect of terrain
  • Human traffic
  • Settlement

…and you can predict what the skiing will be like, depending on where you go!

 

 

A COUPLE OTHER THINGS ABOUT THE TELEMETRY

 

Notice that the example I used includes one of those glitches where the base Total Snow reads 239 inches for one of the hours.  It’s those gremlins who take over at night punishing us humans for relying too heavily on electronic instruments in cold, wet, outdoor environments.

 

NWAC has lots of other measuring stations.  Peruse the site to become familiar with them all!  In addition to Crystal’s "Base & Summit" data, there’s also data from our Green Valley weather plot here.  You may also find telemetry from your other, 2nd favorite ski areas!

 

5 thoughts on “FORECASTING SKI CONDITIONS PART II

  1. I live on the NWAC data and forecasts in the winter. It’s an incredibly valuable resource! Please support them with your donations.
    Shameless plug: if you love NWAC data as much as I do, check out the Windows Phone 7 app. It shows all this data combined with NOAA forecasts and webcams.
    Search for cascadeskier in the marketplace on your phone or click this link:
    http://social.zune.net/redirect?type=phoneApp&id=d1648cd5-ffed-df11-9264-00237de2db9e
    There’s a Windows desktop gadget too:
    http://gallery.live.com/liveItemDetail.aspx?li=a020dad5-6725-4f6f-a12e-f5b777db6642

    Like

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