Friday, February 24, 2017

What's Your Preference, Bounce or Blower?

Ski touring this morning was the epitome of too much of a good thing, at least where we were.  New snow depths based on the highly scientific ski pole insertion were around a meter.

Trail breaking, especially on the ridge we were ascending, was a pig wallow.  Special thanks to the two gorillas (you know who you are) who broke the first 2/3 or so ahead of us and eventually bailed off for a run.  Your efforts are appreciated!

Options for turns were limited.  Diving into steep terrain invited the potential for powerful sloughing. Lower angle terrain required downhill trailbreaking.  Occasionally one could find a happy medium, but as soon as the slope angle backed off, you just augured in.

Nevertheless, there were some visits to the white room.

Those pictures look good, but I'll be honest, the skiing wasn't all that great.  Given the choice between a Goldilocks storm with good "bounce" or over-the-head blower, I'll take bounce every time.  Today was too deep, at least in the backcountry.  My bet is that it will ski better tomorrow after some settlement.

Back to work.


Better one taken by my partner illustrating the downhill "trench" breaking to get over to another line.

Broadcast Interuption

We interrupt our regularly scheduled programming for deep-powder skiing and this message from Squaw Valley/Alpine Meadows, which is mind boggling and requires no embellishment.

Thursday, February 23, 2017

Is the 16/17 Ski Season as good as 10/11?

A buried upper White Pine Canyon on December 24, 2010.  Snow depth at Alta-Collins: 105"
While ski touring this weekend, one of my students had the audacity to ask me if this ski season is as good as 10/11.

Now, in my mind, the 10/11 ski season is the gold standard since I arrived in Utah in 1995 for a variety of reasons.  First, the season started fast, with 62" of snow at Alta-Collins on 1 December.  Second, we crested 100 inches at Alta-Collins before Christmas, opening up adventuring in rocky, high-elevation terrain very early in the season (see above).  Third, there was abundant low-elevation snowpack, greatly improving access to many backcountry areas.  Fourth, the snow just kept coming and, although Alta ski area does not measure snow after the end of the season, a reasonable case could be made that they reached near 800 inches by the end of May (see Alta 800!).

Professor Powder getting Memorial Day Weekend 2011 freshies.  Photo: Tyler Cruickshank.
That's a hell of a yardstick to match, but it turns out this season is close on a few accounts, at least in the Cottonwoods.  In particular, if we look at the snowpack water equivalent at Snowbird, this season (green line) is now neck and neck with 10/11 (cyan line).

Source: NRCS and NWS
Alternatively, if we look at snow depth at Alta-Collins, this morning we sit at 134 inches, whereas on 23 February, 2011, we sat at 141 inches.  Thus, if we base our argument on a snapshot taken this time of year at upper elevations, the two seasons are pretty comparable.

However, there are two other snow-related factors that tip the scales in favor of 10/11.  One is the deeper earlier season snowpack, as can be seen in the snowpack water equivalent above.  The other is the deeper lower elevation snowpack that existed in the Cottonwoods.  Of course, I don't have evidence for the latter except my memories. 

There is one non-snow-related factor that makes 10/11 the gold standard in my mind and it is a personal one.  My son was coming of age in 10/11 and aggressively seeking steep powder lines.  A father's dream!  We had a fantastic season.

Can this season eventually close the gap on 10/11?  That is a tall order.  The snow just kept coming in 10/11, with snowpack water equivalent eventually reaching 75 inches at Snowbird (see graph above).  It could happen, but it will take a hell of a March and April.  Remember in 10/11 how deep of a snowpack even well into June?  

Alta, June 11, 2011
Plus Snowbird stayed open through the 4th of July.

It would be wonderful to have a repeat, but really, does it matter?  Live in the here and now, and the here and now is serving up some great skiing.  

What do you think?

Wednesday, February 22, 2017

How about Some Cold, Moist, Northwest Flow?

Last night's storm delivered nicely across the central Wasatch with most upper-elevation sites reporting a foot or more.

Although we're in a bit of a lull at present, the pattern setting up through Friday generally looks like a good one.  Today is a bit tricky, with the front sort of pinwheeling around and going through various phases of redevelopment, so I'm not sure how it's going to play out, but after that, we're in cold, moist, northwest flow for the rest of the workweek, such as advertised below by the NAM for 5 PM tomorrow (Thursday) afternoon.

A quick look at the NCAR ensemble shows today's lull, but then the likelihood of precipitation increasing in the afternoon.  The waxing and waning of snowfall in the cold, unstable post-frontal environment is very difficult to time, but overall, I would expect we will see periods of snow showers through Friday (the graph below covers only through tomorrow afternoon, but other models support that view).

Much of that snow will be of the low-density, cold-smoke variety in areas where it is not hammered by the wind.


Tuesday, February 21, 2017

The Valley Doth Blow as Hard as the Mountains

Here's an interesting non-alternative fact about our current wind storm.  Peak gusts over the past 24-hour period ending at around 8:30 AM are quite similar in the valleys and on the mountain ridges.

Three sites have reported gusts in excess of 70 mph, two upper-elevation sites near Snowbasin (83 and 73 mph) and one in the western Uintas (77 mph) and these are the highest gusts so far in northern Utah.  So, technically one can find a couple of mountain sites that have the highest gusts in the region.

However, if we move a bit closer to the Salt Lake Valley, we see that peak gusts in the valleys are comparable to those in the mountains.  Here's a selection from MesoWest:

SR-201/I-80 Junction: 69 mph
Park City Ridgeline: 69 mph
Mount Baldy: 68 mph
Stockton Bar: 68 mph
Great Salt Lake Marina: 67 mph
Mid-elevation Mt. Timpanogos: 66 mph
Sandy: 66 mph

So, what gives?  Why is the wind blowing so hard in the valleys, especially overnight?

The peak gust in the Salt Lake Valley occurred at 1200 UTC (0500 MST) this morning at the intersection of SR-201 and I-80, but really at that site it blew quite hard all night long, picking up at around 0200 UTC (7 PM MST) yesterday evening.

Source: MesoWest
The valley winds are being driven by a strong pressure gradient between high pressure centered in the Four Corners area and low pressure over the Pacific Northwest.  The sea-level pressure gradient from southeast to northwest Utah is around 12 mb and concentrated in particular near the Salt Lake Valley. 

This pattern favors pressure-driven channeling within the lower-elevation valleys, so much so that winds are comparable to those experienced on the highest peaks.

The big blow is not over yet.  Hold on to your hats today as a cold front approaches from the northwest and is expected to arrive in the Salt Lake Valley around 7-9 PM tonight, when our flirtation with spring thankfully ends.  

Monday, February 20, 2017

Orographically Forced Clouds and K-H Instability

Today featured strong south to southwest flow impinging on the central Wasatch, leading to the formation of a very pronounced cap cloud over Lone Peak and the Alpine Ridge separating Little Cottonwood and American Fork Canyons.  The cap cloud was illuminated in sunlight when I arrived home from my ski tour this afternoon.

Cap clouds of the type above form due to orographically (i.e., terrain) forced ascent as flow impinges on the mountain barrier and is forced to rise.  It is very common to see such clouds over Lone Peak and the Alpine Ridge in southerly or southwesterly flow.

This morning, the top of the cloud pattern featured a structure that looked liked breaking waves on a beach.  Such patterns are produced by Kelvin-Helmholtz instability (or K-H instability or just K-H for short).  K-H instability is named after Lord Kelvin and Hermann von Helmholtz, 19th century scientists who made important contributions to meteorology and many other scientific fields and is produced when strong vertical wind shear overwhelms the atmospheric stability, resulting in an overturning flow and turbulence. 

Such instabilities can occur in the absence of clouds, and lead to clear-air turbulence, which you have surely experienced.

For better or worse, we spent much of the day in the lee of the Alpine Ridge and just downstream of the cap cloud.  In wind-sheltered area, the turns were creamy and fun and reminded me a little bit of British Columbia.  For the most part, we didn't see much of the Alpine Ridge, but the Pfeifferhorn made a brief appearance before our last run.