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.

Sunday, February 19, 2017

February Is the New April

Today's ski tour was a bit like one you might experience in April.  Snow levels around 7000 feet (but higher overnight).  Wet sponge conditions in which you simultaneously get wet from the inside out and from the outside in.  Decent, creamy conditions above 9000 feet, but snow becoming increasingly cruddy and shallow with decreasing altitude below that point.  Then one returns home and it looks like April.  Warm and partly sunny with little low-elevation snowpack.  

From a snowpack standpoint, this week was one in which the rich (high altitudes) get richer and the poor (low altitudes) get poorer.  In fact, traveling up and down Big Cottonwood Canyon today it was clear that this week was a total and complete disaster for the snowpack below about 8000 feet and especially below 7000 feet.  The snow losses below 7000 feet were visually staggering (I didn't take any photos) and where there was snow, it looked water logged and tired.

I really wish we had a mid-elevation (~7000 foot) snow observing site in the central Wasatch so that we could place events like this into historical context, but we don't.  Not only do we not have a snowpack history at that elevation, but we aren't collecting observations at such elevations today.  There is a SNOTEL observing site at 6000 feet in the North Ogden Valley (Ben Lomond Trail), but the microclimate there is so far removed from the central Wasatch that it is not really representative.

The run of unseasonable warmth is not over yet and will actually be worse tomorrow, when 700-mb temperatures will peak at 0C, through Tuesday morning (0.7C) afterwhich we'll finally start to cool things off.  The mild temperatures are particularly evident in the upper left panel below, showing our estimated temperatures for Mt. Baldy (11,000 feet) based on the NAM forecast.  How about several degrees warming from where we sit at present (the forecast is pretty close to the current observation of 19F this afternoon) through noon tomorrow and then a subsequent peak early Tuesday morning.

The one good thing is that the GFS is advertising a return to cooler weather midweek.  Unfortunately, there's no replacing the low- and mid-elevation snow that's been lost this week.

Friday, February 17, 2017

Deep Trough to Hit Northwest Mexico and I Give Love to Park City

Yes, I know you are probably interested in the President's Day Weekend forecast, but you can get that elsewhere.  We try to look at things differently here at the Wasatch Weather Weenies.  Thus, we're going to Mexico, with a return trip to California and Utah.

Why?  An exceptionally deep upper-level trough will be impacting northwest Mexico Friday and Saturday as part of the storm system that is also sweeping across the western United States.  The GFS forecast loop below shows the band of heavy precipitation sweeping through the Mexican states of Baja California, Baja California Sur, Sonora, and Sinaloa with the 500-mb trough.

That 500-mb trough is exceptionally deep for such a low latitude.  As it sweeps over Cabo San Lucas, the 500-mb heights are lower than anything observed during this 3-week period in the Climate Forecast System Reanalysis record for 1979-2009.  Basically, the jet stream has decided its had enough of the cold mid latitudes and is dipping down and flirting with the tropics.

Prior to that, as the upper-level trough moves down the California coast, it is accompanied by a surface cyclone with unusually low sea level pressures.  The NAM forecast images below, valid at 5 PM MST this afternoon, 5 AM tomorrow morning, and 5 PM tomorrow afternoon, show the cyclone directly down the California coast.  The Santa Ynez Mountains look to get a pounding today as they are oriented perpendicular to the landfalling atmospheric river ahead of the low center.  

Utah will see warm-frontal precipitation develop late today.  If you look at the top panel above,  you will see low-level southeasterly flow.  This is a situation where Deer Valley and PCMR will likely see the most precipitation.  Brighton often does well and sometimes the Supreme area of Alta.  Lesser amounts typically as one moves westward.  Indeed, even the 12-km NAM produced a 3-h precipitation forecast for the period ending at 0600 UTC (11 PM MST) tonight that has more precipitation east of Alta (red dot) than west.

The NCAR ensemble picks up on this a bit.  Note the shift to slightly higher values from Alta-Collins (top) to Brighton (bottom, note scale change).

The change is not large, but these two locations are separated by only a couple of grid points, so that's pretty good for a model with 3-km grid spacing.  

The latest 12Z NAM is putting out about 0.35 inches of water through tomorrow morning at Alta.  I've been burned more times than I'd like to admit in these warm frontal events as they sometimes underproduce, especially during their early stages.  Thus, I'm thinking of something like 2-5 inches of snow for Alta and Snowbird and 4-8 inches for upper elevation areas along and east of the Wasatch Crest, including Deer Valley, through 8 AM tomorrow morning.  Snow levels could flirt with the base of PCMR this afternoon, but otherwise should remain at or below 7000 feet.  

So for you Park City skiers, Professor Powder gives you a little love today.  The real question is will Mother Nature?

Thursday, February 16, 2017

California Megafloods

California is a land of weather extremes.  Most of the California's precipitation falls from December through March, during the so-called "wet-season."  However, the precipitation that falls each wet season varies greatly, leading to precipitation extremes that include seasonal or multi-year droughts and pluvials (periods of increased rainfall). I hesitate to use the word "cycles" to describe the fluctuations between these precipitation extremes because they are not regular.  Instead, it is probably best to say that the precipitation climate of California is highly variable.

Only last year California was mired in extreme drought.  That has certainly changed this year with heavy precipitation and remarkable mountain snowpack.  However, as impressive as this past winter has been so far, the potential exists for even greater precipitation.  Geologic evidence suggests that massive flooding strikes California every 100-200 years (some studies suggest a longer return interval).  A nice article by Dr. Lynn Ingram discussing these Megafloods appeared in the Scientific American four years ago (available here).
Source: Scientific American
In the article, Dr. Ingram writes,
"The only megaflood to strike the American West in recent history occurred during the winter of 1861-62. California bore the brunt of the damage. This disaster turned enormous regions of the state into inland seas for months, and took thousands of human lives. The costs were devastating: one quarter of California’s economy was destroyed, forcing the state into bankruptcy. Today, the same regions that were submerged in 1861-62 are home to California’s fastest-growing cities. "
During that season, Los Angeles observed 66 inches of rain.  Much of the Central Valley was under water.  

Although one might hope that dams and levees would help today, recent studies suggest that such infrastructure would be overwhelmed by a several-week sequence of storms of the type observed during the 1861-62 winter.  A recent USGS report examining such a scenario pegs the damage estimates for California in the neighborhood of $0.5 to $1 trillion (see Overview of the ARkStorm Scenario).

For more on this, as well as extreme drought, see Dr. Ingram's excellent book, "The West Without Water," which we've reviewed in the past and I consider essential reading for anyone interested in the weather and climate of western North America.

Wednesday, February 15, 2017

Catching Up on Climate Change

Thanks to world travels, inversions and air pollution, and active storm cycles, I haven't had a chance to throw some climate tidbits at you in some time.  Here goes.

2016 Warmest Calendar Year on Record Globally

I'm late to the party on this one and you probably knew this already, but 2016 was the warmest calendar year on record, inching out 2015.  Collectively, those two years easily represent a new "high" for the planet, well above anything else in the instrumented record.
Source: National Centers for Environmental Information
Tough to say if 2017 will set another record.  I wouldn't be surprised if we pushed it a bit higher, or if we settled back a bit as has often happened during the long-term warming trend over the past few decades.  If the latter occurs, don't fall talk of a global warming pause or hiatus.  The train has left the station and we're on our way to a warmer future.

No Record for Utah

The statewide average temperature in 2016 for Utah was in rare territory, ranking as the 6th warmest in the instrumented record, but still lagged behind the remarkable 1934.

Source: National Centers for Environmental Information
January 2017 Close to the 20th Century Average for Utah

January felt a bit more like an old-time winter this year and the data bears that out as the statewide average temperature was nearly dead on the 20th century mean.

Source: National Centers for Environmental Information

Record Low Arctic Sea Ice Extent 

The National Snow and Ice Data Center reported last week that record low Arctic ice extents have been observed from October through January.


Tuesday, February 14, 2017

The Jackson Windstorm

On the evening of Tuesday, 7 February (MST), strong, damaging winds struck the Jackson, WY area, snapping 17 steel power poles along the Moose-Wilson Road and, cutting off power to Teton Village and Jackson Hole Mountain Resort.  

Source: Lower Valley Energy, via FirstTracksOnline.
After several days of closure, Jackson Hole Mountain Resort reopened yesterday (Monday).

I thought we would take a look today at the events conspiring to wreak this havoc, although I confess I have more questions than answers at this time.

There were no wind observations provided to MesoWest in the immediate area of the damage.  As such, for this preliminary write up, we are forced to rely on observations from the vicinity.  The first is from the Jackson Airport, which reported sustianed winds reaching 40 mph and a peak gust just above 60 mph at about 0100 UTC (6 PM MST) before observations ceased. The wind direction during this period was S-SW.

The other nearby site is at the summit of Jackson Hole Mountain Resort.  The peak gust there was just above 75 mph at just after 0000 UTC (5 PM MST, note the differing time axis).  Note that at this elevation, the sustained winds and the gusts during this period are not much stronger than those observed in the late afternoon and evening of the prior day.  This contrasts with the Jackson Hole Airport where winds were much strong, indicating that something happened to cause anomalously strong valley winds.

At 1800 UTC 7 February, about 6 hours prior to the wind event, regional analyses from the GFS show a broad, low amplitude ridge across the western United States with the ridge axis centered over Nevada.  An intense jet, with wind speeds of over 75 m/s (150 knots) extended across far northern California and Nevada.  At 700 mb (10,000 ft above sea level, roughly crest height near Jackson Hole Mountain Resort), the flow was southwesterly and featured strong warm advection (i.e., winds transporting warm air into the region from the southwest).  Basically, Jackson was in a warm-frontal zone.

The influence of this strong warm advection is clearly seen in the temperature time series from both the Jackson Airport and the summit of Jackson Hole Mountain Resort (note the differing time axes).  At both sites, temperatures climbed prior to the wind event.  The climb at the summit of Jackson Hole Mountain Resort (bottom image) was steady throughout the day, whereas at Jackson Hole Airport, it was more abrupt and occurred in the 2 hours prior to the wind storm.  This often occurs with warm-frontal passages in which the cold air remains more persistent at low levels, especially deep mountain valleys.   Note that the peak wind gusts may have occurred at the time of peak temperature, although the power outage precludes any chance to confirm that.

At 0000 UTC 8 February (5 PM MST 7 February), just prior to the wind event, an intense zonal (westerly) jet extended across northern California, Nevada, and Utah, just south of Jackson Hole.  Temperatures at 700-mb had warmed significantly and Jackson was basically in the "ridge" of warmest air, with cold advection just upstream over Idaho.  The surface trough, which is poorly analyzed at this resolution, was also very close to Jackson.  

By 0600 UTC 8 February (11 PM MST 7 February), the upper-level flow over Jackson was veering and becoming WNW in response to the building upstream ridge and Jackson was in the wake of the ridge of warm air at 700 mb and experiencing regional-scale cold advection.

Analyses from the High Resolution Rapid Refresh (HRRR) show a surge of strong southwesterly flow up the eastern Snake River Plain just prior to the winds storm.  Note in particular the "break-in" of strong southwesterly to westerly flow into the Jackson Hole region from 2300-0100 UTC below.

HRRR surface winds at 2300 UTC 7 February
HRRR surface winds at 0000 UTC 8 February
HRRR surface winds at 01 UTC 8 February
There is evidence of of a band of convection sagging through the Snake River Plain during the wind event.  The lack of echoes over Jackson, however, is somewhat meaningless due to its remote distance from the radars, which means the coverage is terrible.

Source: NCAR/College of DuPage
Source: NCAR/College of DuPage
So, given the limited data and the limited time I have to investigate this event, let me provide some early speculation.  I suspect that an old occluded front and accompanying tongue of warm air passed across the Jackson area at the time of maximum winds.  This feature was accompanied by a surge of strong SW-W flow.  This is fairly consistent with my forecast that morning in which I warned of the potential for strong winds in the Wasatch Range (The Big Bad Wolf Is Coming to Town).  What is less clear is whether or not the strongest winds were produced by some sort of terrain-driven circulation as that feature moved through, or potentially some sort of precipitation-induced feature if the convection over southeast Idaho extended into the Jackson area.  

I am inclined to suspect the former, but only a careful investigation of this event in which we examine the high-resolution radar data, all surface wind observations, and perhaps do some numerical modeling, will allow us to determine if that hypothesis holds water.  If you were in the Jackson area, please share your observations of the weather on that evening as they could prove useful.

Sunday, February 12, 2017

The Cottonwoods Sure Clean Up Good, Part II

You know those days when it feels great just to be alive?

Today was better.

Following up on yesterday's post about how the Cottonwoods sure clean up good, today was bluebird and the snow was fun, although powerful sluffs kept us off steep terrain.

Bottom of the first run.

Big views in all directions.


Sloughed out Hogum Ridge.

So much terrain, so little time...

SR-210 below.

Runnels below Fridays snowline.  February in the Wasatch right?  Let's hope that doesn't happen again until April. 

Surface hoar.  Vapor deposition in action after just one clear night.

Sweet dreams tonight for sure.