Monday, February 27, 2017

Meteorological Winter Going Out with a Bang

After abandoning us for a stretch in February, it is clear that Meteorological Winter (the months of December, January, and February) is going to go out with a bang as snow impacts the morning commute across much of the Salt Lake Valley and the northern Wasatch Front today.

The large-scale setup for this event is worth a peak as it features many of the characteristics that we often see when an upper-level trough swings across the Great Basin.  At 2000 UTC (1700 MST) yesterday, the system was "vertically stacked" along the Pacific Northwest coast with the 500-mb low center (as indicated by the 500-mb height contours in black) located nearly over the sea level pressure low (as indicated by color contours).  To the south, a pronounced lee trough existed downstream of the Sierra Nevada, from which a surface trough extended into western Utah.

As the upper-level trough slid southward and eastward overnight, the Great Basin trough extended northeastward across northern Utah and become the locus for surface development and cold-front formation, with precipitation immediately upstream becoming more widespread.

It is that area of precipitation that is now bringing snow to the Salt Lake Valley and northern Wasatch Front, and will eventually impact Utah County.  The latest radar loop shows scattered precipitation over Utah County and far southern Salt Lake County, but otherwise fairly continuous snowfall from roughly 6200 South to Ogden.

Really, this is not a worst-case scenario because temperatures are modest and road crews have been out, but it's still bad.  Utah Commuterlink traffic flows show a pretty horrendous picture with low speeds (0-30 mph) along many of the main highways in Salt Lake, Davis, and Weber Counties.  Note how Utah County remains "in the green."  Weather, like politics, is local, and they've escaped the snow impacts so far.

Things are looking good for a few inches of snow to pile up on the campus grass this morning.  The system has already been a good producer in the mountains (6 inches at Alta-Collins, perhaps 9 inches at Snowbasin-Boardwalk).  Looks like free refills until the front pushes through later today.  

Sunday, February 26, 2017

Weather Scenes from Little Cottonwood

A quick shout out to begin today's post to Mrs. Professor Powder, who celebrated her big five-oh in style today.  I must confess that I did pull the government weather-control lever to ensure bluebird skies and high-speed cruising for her birthday.  

She has put up with my weather weenieness for just over half of those years and today was no exception.  So much to see!  Yes, the views were great, but did you spot the 22-degre halo?

How about wind transport?  The photo below as taken about 1 PM.  At the time, winds on Mt. Baldy were a rather unimpressive 17 mph with gusts to 32.  No mind, there's plenty of low-density blower to transport and that speed will do it with snow like that.  We departed soon after, but I suspect that wind deposition rates increased further with the winds this afternoon.  

With so much dry snow around, not just on the snowpack, but also in the trees, one could practically pick out the gusts by eye.  It was quite impressive to see these patches of stronger winds and snow transport and lofting.  

The wind also made for some spectacular lenticular clouds and snow-filled ridges.  

One can't see the Pfiefferhorn from Alta, but I've heard reports that it was covered by a pretty cap cloud at times today.

There's a recently published paper that suggests the lofting of snow from the ground and trees can, under the right circumstances, serve as effective seeding agents for producing snow.  Many clouds contain supercooled water drops that are colder than 0ÂșC, but are not yet frozen.  They need a small particle, known as an ice nuclei, to begin the freezing process.  The best ice nuclei have structures similar to ice.  Small clay particles can be good, but nothing is better than ice itself.  

At issue for today is whether or not this process was operating in the clouds over the Wasatch Range.  It was very clear when I returned home that the small cumulus clouds over the Wastach were composed in part of supercooled water droplets.  Such clouds typically feature sharp edges, as seen below.  At low levels, however, there was snow.  It is impossible to say, however, how much of that snow is from wind transport, how much is simply growing and falling out of the clouds from natural ice nucleation, and how much might be related to ice nucleation by wind transported and lofted snow. 

So many questions, so little time!

Saturday, February 25, 2017

Snowpack Extraordinaire: North Ogden Valley

As many of you are aware, the microclimate of the North Ogden Valley holds a special place in my heart (see Pound for Pound the Snowiest Place in Utah).

Source: Secrets of the Greatest Snow on Earth
Every time I go there in the winter or spring, I'm blown away by the snowpack.  Today I needed to get some work done, and battling the weekend crowds in the Cottonwoods wasn't very inviting, so my son and I shot up to the Ogden Valley for some skinny skiing at the North Fork Park trail system maintained by Ogden Nordic.

It's hard to believe that North Fork Park is at an elevation of about 5800 feet.  I check the map every time I visit there.  The snowpack is remarkably robust, blowing away anything at a comparable elevation on the back of the central Wasatch.  The scene today was a winter wonderland.

I didn't measure snow depth anywhere, but the Ben Lomond Trail SNOTEL site is nearby and at an elevation 5820 ft.  For 24 February, the median snowpack water equivalent is a robust 17.8 inches and we are running well above that this year with 27.9 inches (this is not a record for the date).

To put those numbers into perspective, they are not that different from the Mill-D North SNOTEL at 8967 feet in Big Cottonwood Canyon, which has a median on 24 February of 19.1 inches and currently sits at 25.6 inches.

If free and clear from traffic, the drive to North Fork Park from downtown Salt Lake City is an hour and five minutes, not that long at all.  I usually take the slightly longer Trappers Loop route up the backside of Snowbasin to enjoy the views.

Of course, despite opting to go up to North Fork Park in part to avoid the Cottonwood congestion, we still got snarled thanks to a bad accident along I-15.  I can't win!

On the plus side, it did give us some time to check out some beautiful cloud formations over Snowbasin. Note in particular the transition from orographic convection at low levels, indicative of unstable air, to wave clouds aloft, indicative of more stable flow.  Note also how those wave clouds were only produced over the higher terrain and are not evident over Ogden Canyon.

How those differing clouds interact to produce the snow that fell today over Snowbasin and the Ogden Valley is a question I'll ponder tonight.

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?