Tuesday, January 19, 2021

Yesterday's Snowmaggedon

January has brought a whopping...wait for it...16.5 inches of snow to Alta through January 19.  That's not a lot, but many driving through Little, Big, or Parley's canyon got bit by the red snake anyway.  

Highway impacts from winter storms depend on several factors.  Snowfall amount can matter, but snowfall intensity, pavement temperatures, traffic, timing, and other factors can cause even storms with relatively small totals to cause huge problems.  

Twenty-four hour snowfall total in the central Wasatch through this morning are in the 1-3" range.  However, most of that snow fell in the late afternoon with relatively high intensity, especially west of the crest, strongly affecting road conditions in the canyons.  

Source: NCAR/RAL

The situation at the time was a bit unusual.  Winds at mountaintop level (e.g., on Mt. Baldy and at the top of the Snowbird tram) were weak and northerly as we were beginning the transition to the easterly flow that would develop overnight and produce downslope winds along some areas of the Wasatch Front.  However, upstream, northwesterly flow was impinging on the Wasatch Range over the Salt Lake Valley.  Some light easterlies were observed in the Olympus Cove area, but I suspect this was produced by local outflow from the precipitation area along the west slope of the Wasatch.  

The afternoon sounding was consistent with the surface-based observations with northwesterly flow at low levels and very light flow at crest level (700 mb or 10,000 feet). 

Thus, it appears that shallow, low-level upslope flow led to the frequent initiation of shallow convection over the westernmost portions of the central Wasatch.

Additionally, the layer from about 750 to 600 mb was between -10 and -20˚C, a temperature range known as the dendritic growth zone.  This is a range in which ice crystals, when conditions are right, can grow rapidly.  I was out walking yesterday with a world-famous meteorologist and we both commented about how even the smallest cumulus clouds were producing virga.  

Finally, weak flow at crest level, these crystals had no where to go.  The fell out predominantly at and west of the crest.  

This led to traffic armageddon in all three canyons as down-canyon traffic was picking up at the end of the day.  Below is the UDOT traffic camera at Alta showing the dreaded red snake at...wait for it...6:22 PM.  
Source: UDOT

At that time, it appeared it wasn't even snowing anymore and I was seeing tweets claiming it took 2-2.5 hours to get down the canyon.  All of this, despite the fact that the Snowbird snow cam showed only about 3 inches on the stake.  

Source: Snowbird

And, to add insult to injury in this low-snow year, the strong winds last night have done their damage, transporting and beating up the snow.  

I miss real winter. 

Friday, January 15, 2021

Big Japanese Snows

The Tokyo Climate Center of the Japan Meteorological Agency just released a report discussing the heavy snowfall observed in Japan in recent weeks.  If you want the gory details, the report is available here.  The figures below are from the report.  

As detailed in the report, beginning in mid December, an anomalous jet-stream pattern led to frequent cold air outbreaks from interior Asia over the Sea of Japan, which was anomalously warm.  72-hour all-time or January snowfall records were broken at 19 stations, spanning nearly the entire length of Honshu.  

There are a couple of things that stand out for me in the image above.  First, there are some stations well inland from the Sea of Japan that set records.  These occurred during the mid-December event in which strong flow enabled deep inland penetration and orographic enhancement of sea-effect snowfall (see our previous post Gosetsu Chitai Dumpage for more information).  

Second, there are a few stations on or near the Pacific coasts of northern Honshu and Hokkaido Islands that also set records, including on the far east coast of Hokkaido.  These are not discussed explicitly in the report, and I wonder if they might reflect the influence of a passing mid-latitude cyclone rather than sea-effect spillover.  That might be most likely in far eastern Hokkaido.  Something to look into in a future life when time permits.

Maximum snow depths exceeded the maximum on record at one site and the maximum for January at four others.  If you squint, you can see a few sites in central Honshu and one in northern Honshu (probably Sukayu Onsen) that reached a snow depth of more than 300 cm (120 inches). 

Note also the stark contrast across Honshu.  This is actually not that unusual, but it's still remarkable.  Traveling by train, including Shinkasen (bullet train) from Tokyo to the Hokuriku district of central Honshu near the Sea of Japan (or vice versa) can be a mind boggling experience as you move through a remarkable climate gradient.  There's currently no snow in Tokyo, but more than 3 meters in the mountains near the Sea of Japan.  

In 2017, I left the Myoko Kogen where it was snowing heavily and the owner of the Myoko Mountain Lodge had to drive me inland to catch my train because the nearby stations were closed.  Here's how things looked the night before I left.

We had a difficult drive, but I caught my train.  The snowfall dropped off quickly inland.  I can't remember exactly where I took this photo on the Shinkasen to Tokyo, but the mountain in the distance is Mt. Fuji and you can see there is no snow on the ground.  

Tokyo is near sea level, but so are the cities on the Sea of Japan coast that currently have around a meter of snow.  Thus, even at the same elevation, there is a stark contrast.

The snowiest cities in the world are located on the Sea of Japan coast of Honshu and Hokkaido Islands.  Many average over 200 inches a year.  Huge "Gosetsu" winters (heavy snow winters) in the past have crippled those cities.  Here's a great video of Nagaoka in the 1963 Gosetsu Winter. 

All of this is a reminder that while Utah is in the grips of drought, Mother Nature can still bring it.  

Tuesday, January 12, 2021

The Difference between the Inversion and the Haze/Pollution Layer

Many people equate pollution in the Salt Lake Valley with the inversion, but they are different but related phenomenon.

Understanding the difference between the two explains unusual days like yesterday when haze and smog filled the Salt Lake Valley through a relatively deep layer, extending up to about 7500 feet.  This occurred not because the inversion was deep, but because the inversion was elevated.  In addition, the atmosphere below the inversion featured weak stability, enabling pollution to mix through a relatively deep layer.  

The image below includes a photo taken yesterday morning from Alta Ski Area and the sounding taken that afternoon at the Salt Lake City International Airport.  Haze and smog filled the Salt Lake Valley to an altitude of about 7500 feet where there was a sharp boundary to clearer air (indicated by the dotted line).  The afternoon sounding showed that in that haze and smog layer, the stability was relatively weak. Meteorologists refer such a region as a mixed layer because the weak stability promotes vertical mixing.  

Sounding source: SPC

However, at about 7500 feet (7400 feet in the sounding), there was a pronounced inversion in which temperature increased rapidly with height.  This put a lid on the mixed layer, preventing mixing with the free atmosphere aloft.  Thus, pollution wasn't trapped very near the surface, but instead was able to mix to the top of the mixed layer at 7400 feet, but no higher.   

This situation is similar to what commonly happens in the Los Angeles basin where the marine boundary layer typically features a mixed layer at low levels capped by an inversion.  

The reality is that the situation yesterday from an air quality standpoint was probably better than if the inversion were in its usual position very near the valley floor.  When that occurs, pollution is trapped in an even shallower layer.  

I'm interested to see how things evolve today.  Overnight, the mixed layer was destroyed for two reasons.  First, temperatures near the valley floor cooled, while those between the surface and the elevation of the top of yesterday's mixed layer (i.e., near 7400 feet) increased.  This has produced a sounding that is very stable.  

Source: SPC

If there was snow on the ground and there wasn't a trough approaching, I would say our goose is cooked.  However, the lack of snow on the ground will enable the sun to produce a shallow mixed layer today (although probably not as deep as yesterday).  Thus, I suspect the haze/pollution layer won't be as deep today, but will probably envelop the upper benches this afternoon.  Hopefully the trough passage tomorrow and tomorrow night will scour things out and hit the reset button on air quality.

Sunday, January 10, 2021

Valley Stratus

Low overcast clouds that fill the lower elevations of mountainous regions are sometimes referred to as valley stratus.  They can occur any time of year, but are most common during the cool-season when the energy input from the sun is low, enabling the stratus to be more persistent.  

We are experiencing valley stratus in the Salt Lake Valley today, with mostly cloudy skies.

However, the highest elevations of the Wasatch are above these clouds.  Note the contrast below between the lower and upper mountain at Snowbird.

Source: Snowbird

Source: Snowbird

Satellite imagery shows an interesting transition in the valley stratus today.  At around noon, the stratus was confined to near the Great Salt Lake, which was fully covered by clouds. 

Visible satellite imagery at 18:56 UTC (11:56 AM MST). Source: College of Dupage

An hour later, stratus was developing along western slope of the Wasatch Range and within the Salt Lake and Utah Valleys immediately upstream.  

Visible satellite imagery at 18:56 UTC (11:56 AM MST). Source: College of Dupage.

This morning's sounding from the airport is typical of valley stratus situations.  At low levels, there's relatively cool, moist air, capped by a strong inversion that in this case is based at about 725 mb (about 9000 feet above sea level).  

Source: SPC

The stratus forms near the top of the cool, moist layer, just beneath the inversion.  Conditions at. higher elevations are spectacular due to the dry air aloft, but the valley remains cool. 

If this were summer, the energy input from the sun would be sufficient to warm the valley airmass enough to break up or completely dissipate the clouds.  This time of year, however, they often persist unless other atmospheric changes contribute to their demise.  

This situation differs from pollution inversion events because the inversion is based quite high.  Thus, pollution in the valley, while still trapped to some degree, is able to mix to about 9000 feet, so air quality today is good.  Over time, however, the inversion will lower, which will dissipate the clouds, but also trap the pollution in a shallower layer.  I would expect to see more haze tomorrow, for example. 

Valley stratus events are even more common in wetter environments, such as the Coast and Columbia Mountains of British Columbia and the European Alps.  When I taught at the University of Innsbruck, the students were required to forecast the likelihood of valley stratus.  

The ability to recognize valley stratus events is valuable for mountain adventures.  If you woke up in Innsbruck this morning, you were greeted by grey, depressing skies.

Source: foto-webcam.eu

It might also be cloudy at upper elevations, but in the Inn Valley, it is always worth a look at the web cams.  Indeed, the mountains near town were above the clouds, a short funicular and tram ride away.  

Source: foto-webcam.eu

Just like Utah, at least meteorologically. 

Saturday, January 9, 2021

The Lure of Dutch Draw

I was deeply saddened to learn of the death yesterday of a 31-year-old snowboarder in Dutch Draw, a backcountry area along the Park City Ridgeline and often accessed from the 9990 chairlift at Park City Mountain Resorts.  My deepest condolences to family and friends. 

This one hit me in the gut harder than most, I think in part because there have been so many deaths in Dutch Draw over the years.  The Utah Avalanche Center has an extensive record of avalanche fatalities in Utah (available here) and it appears this is the 4th since 2005.  The accident reports suggest that in all cases, the victims entered the backcountry after riding the 9990 chairlift.   

Although knowledge of terrain, weather, and snowpack is important for evaluating avalanche risk, our judgement and ability to perceive risk is often clouded by other factors.  Avalanche accidents happen when the perception of risk does not match the reality.  Ian McCammon has investigated the role of heuristics, mental shortcuts, rules of thumb, and other factors that contribute to avalanche accidents, identifying six that can be abbreviated into the easily recalled acronym "FACETS" (image below from 14erskiers.com).  

Source: https://14erskiers.com/blog/wp-content/uploads/2016/12/FACETS-.png

I can identify situations over the years in which each of these contributed to questionable decision making on my part.  If I were a Vulcan, I might be able to objectively evaluate risk, but I'm human.  Powder or touring objectives can be like the apple in the Garden of Eden, a forbidden fruit that is very difficult to resist.  

Dutch Draw is an area these traps are well disguised by the cheese.  In-bounds powder gets tracked quickly, yet you can see powder beyond the ropes.  Tracks/scarcity begins to ratchet up your desire to go out of bounds.  You've been skiing in-bounds and the snow seems fine.  You've built Familiarity with the snowpack, but one that has much lower avalanche risk due to skier compaction and mitigation efforts compared to what lies beyond the ropes.  You've developed false sense of security.  For Acceptance, you want to boast to friends about the great powder run you had in Utah, so you're more likely to push it.  Yes, you just passed a backcountry gate warning of considerable hazard, including a sign you could die, and you think the snowpack is a bit sketch, but you've come this far and turning around is hard.  You've made the Commitment.  That morning, you rode on the lift with a local and regular resort rider who said that yes, people often do ski Dutch Draw.  Locals surely know something right?  They have an Expert Halo.  Your college buddy from Boston thinks it will be fine and eggs you on in a form of Social Facilitation.  

Those are hypothetical examples.  The factors contributing to avalanche accidents vary.  Dutch Draw is a place where powder fever is very contagious.  You can see fresh powder from the resort and it is easily accessed.  It is hard to say no.  

When I think about times I've exhibited questionable judgement in the backcountry, they have usually been due to heuristic traps.  The consequences have fortunately not been severe, and in many cases I can thank partners for speaking up and raising concerns.  In others, perhaps it was just luck.  

We have been dealt a house-of-cards snowpack for the 2020-2021 ski season.  It is weak and snowpacks like this do not heal quickly nor homogeneously.  When it starts to snow again...and it will start to snow again...recall the FACETS and try and think like Mr. Spock rather than Captain Kirk.  

Friday, January 8, 2021

An Open Letter to Mother Nature

Dear Mother Nature:

I know that the computer models suggest that the storm tonight and Saturday morning is a small one and, with each model run, seems to get smaller.

The 0600 UTC NAM now produces 0.15" of water and 2.6" of snow at Alta.  The GFS also generates only 2.6" of snow.  Similarly, the SREF has converged around solutions that suggest a dust-on-crust event, with 21 of the 26 members calling for 3" or less and the snowiest member producing 6"

However, I also know that these models are imperfect.  We try our best to translate physical understanding of how you operate into equations that can be solved on computers and we're getting better at it, but we're still not as good as you.  

It's been a long year and in addition to missing our friends and family, we now miss snow.  I ask that you and your sons the Snow Miser and the Heat Miser come to an agreement to produce a decent storm for northern Utah.  I recognize that it is not Christmas and that this is an exceptional request, but instead of winter, we're having an endless November when we should be enjoying the best skiing of the season.  

Below is a photo of good times when you've been able to successfully broker an agreement between your sons in the past.  I suspect that concessions are needed.  If so, we will gladly allow Heat Miser to torture us with a couple of days of 100+ heat in July for a real powder day tomorrow. 


Respectfully Yours,

Jim Steenburgh
Humble Meteorologist